Office of Operations
21st Century Operations Using 21st Century Technologies

Transportation Systems Management and Operations Benefit-Cost Analysis Compendium

CHAPTER 5. ARTERIAL OPERATIONS

# Case Name Benefit-Cost Analysis (BCA) Model Actual or Hypothetical Case
5.1 Hypothetical Preset Arterial Signal Coordination TOPS-BC Hypothetical
5.2 Adaptive Traffic Signal Control in Greeley and Woodland Park, Colorado Custom In-house Analysis Actual
5.3 Adaptive Traffic Signal Control Custom In-house Analysis Hypothetical
5.4 Hypothetical Roundabouts TOPS-BC Hypothetical
5.5 Effectiveness of Roundabouts in Maryland Custom Stand Alone BCA Model Focused on Safety Benefits Actual
5.6 Effectiveness of Arterial Management in Florida TOPS-BC Actual

Case Study 5.1 – Hypothetical Preset Arterial Signal Coordination

Strategy Type:  Arterials
Project Name Hypothetical Preset Arterial Signal Coordination
Project Agency Based on Data from Denver COG
Location:  Principal Arterial
Geographic Extent:  2.8 Mile Corridor
Tool Used:  TOPS-BC Tool

Note: Chapters 2, 3, and 4 of this Compendium contain a discussion of the fundamentals of benefit-cost analyses (BCA) and an introduction to BCA modeling tools. These sections also contain additional BCA references.

Project Technology or Strategy

Arterial signal coordination involves the coordination of traffic signal timing patterns and algorithms to smooth traffic flows—reducing stops and delays and improving travel times.  Agencies can implement this strategy on a small corridor, a limited grid, or region-wide. The sophistication of the timing coordination can also vary from simple preset timing programs to more advanced traffic actuated corridor systems, to fully centrally controlled applications.

Program and Project Goals and Objectives

Since 1989, Denver Regional Council of Governments' (DRCOG) Traffic Operations Program has been working with the Colorado Department of Transportation and local governments to coordinate traffic signals on major roadways in the region.  DRCOG designed the program to reduce traffic congestion and improve air quality.  DRCOG was one of the first metropolitan planning organizations (MPO) to conduct such a program, and remains the leader among the very few MPOs throughout the United States involved in traffic signalization efforts.  Table 8 provides a snapshot of DRCOG's 2012 annual benefits summary of projects.  Links for each project provide signal timing briefs (individual benefits summary reports for each project).  To view the data shown in Table 8, visit https://drcog.org/sites/drcog/files/2013%20Traffic%20Operations%20Program%20projects.pdf.

Table 8. Denver Regional Council of Governments 2012 Annual Benefits Summary of Projects.
Project Limits Number of Signals Jurisdiction (Operators) Project Type Benefits
Travel Time Reduction (Hours/day) Fuel Consumption Reduction (Gal/day) Pollutant Emissions Reduction (lbs/day) Greenhouse Gas Emissions Reduction (lbs/day) User Savings ($/day)[1]
T13-1 Alameda Ave. Sheridan Blvd. to Marion Pkwy. 29 Denver Capital Improvement Signal Timing Project 671 406 99 8,451 $15,850
T13-2 University Blvd. Alameda Ave. to Hampden Ave. 19 Denver, Englewood, CDOT Capital Improve­ment Signal Timing Project 643 401 88 8,287 $15,150
T13-3 Arapahoe Blvd. University Blvd. to Waco St. 29 CDOT, Centennial, Greenwood Village, Aurora, Arapahoe County Capital Improve­ment Signal Timing Project 1,056 547 132 11,352 $24,550
T13-4  US-85 Bromley Lane to 104th Ave. 10 CDOT, Brighton Capital Improve­ment Signal Timing Project 290 130 30 2,710 $6,550
T13-5a 120th Ave. Nickel St. to Holly St. 30 CDOT, Thornton, Northglenn Capital Improve­ment Signal Timing Project 1,097 590 151 12,201 $25,600
T13-5b Huron St. 128th Ave. to 104th Ave. 12 Westminster, Northglenn, CDOT Signal Timing Project 502 266 67 5,541 $1,750
T13-5c Sheridan Blvd. Aspen Creek Dr. to 118th Ave. 9 Broomfield, CDOT, Westminster Signal Timing Project 309 157 35 3,267 $7,200
T13-6 84th Ave./Huron St. 84th Ave: Huron St. to Washington St.; Huron St: 84th Ave. to Connifer Rd. 12 Thornton Capital Improve­ment Signal Timing Project 240 75 18 1,542 $5,400
T13-7 Wadsworth Blvd. 64th Ave. to 108th Ave. 33 CDOT, Westminster, Arvada Capital Improve­ment Signal Timing Project 532 250 63 5,214 $12,300
T13-8 Parker Rd. Chambers Rd. to Cottonwood Dr. 12 CDOT, Aurora, Arapahoe County, Centennial, Parker Capital Improve­ment Signal Timing Project 886 447 99 9,278 $20,550
T13-9 Church Ranch Blvd./104th Ave. Wadsworth Pkwy to Sheridan Blvd. 12 Westminster, CDOT Capital Improve­ment Signal Timing Project 361 190 45 3,924 $8,450
T13-10 State Hwy 52 I-25 Frontage Rd. to Frederick Way 8 CDOT Signal Timing Project 327 166 38 3,464 $7,550
T13-11 State Hwy. 7 I-25 to Colorado Blvd. 6 Thornton, CDOT Signal Timing Project 111 61 13 1,254 $2,600
T13-12 Martin Luther King Blvd./31st Ave. Downing St. to Colorado Blvd. 16 Denver Capital Improve­ment Signal Timing Project 107 79 22 1,641 $2,550
T13-13 North Quebec St. Alameda Ave. to 56th Ave. 30 Denver Capital Improve­ment Signal Timing Project 433 222 62 4,604 $10,050
T13-14 Leetsdale Dr. Alameda Ave. to Mississippi Ave. 19 Denver Capital Improve­ment Signal Timing Project 759 385 92 7,983 $17,650
T13-15 Speer Blvd. Gilpin St. to Federal Blvd. 32 Denver Capital Improve­ment Signal Timing Project 467 230 55 4,760 $10,800
[1] Fuel @ $3.51/gal., time value @ $21.43/hr.
Source: DRCOG

Data

DRCOG collects data prior to and after deployment of signal timing to evaluate benefits.  Figure 12 provides data for Alameda Avenue, the first 2013 project listed in Table 8.  Visit http://www.drcog.org/documents/T13-01_Signal_Timing_Briefs_AlamedaAve.pdf for a full sized version of the flyer.

Screen capture of a two-sided brief that promotes the benefits of a particular signal timing improvement project on Alameda Avenue, including travel time benefits valued at about $4 million per year.
Source: DRCOG
Figure 12. Screenshot. Signal Timing Brief for Alameda Avenue.

Data collected include vehicles per day, length of the corridor, travel time in both directions for three time-periods (morning peak, midday/off-peak, evening peak) both before and after implementation, number of signals affected, and timing revisions. The signal timing briefs also provide estimates of daily benefits for five performance measures including vehicle hours of travel, fuel consumption, time and fuel costs, total greenhouse gas emissions, and total criteria pollutant emissions.

According to the Alameda Avenue Signal Timing Brief, "Adjustments to signal timing are key to ensuring the smoothest possible flow for drivers, saving time and money.  Signal timing also minimizes greenhouse gas emissions and other pollutant emissions, preserving and enhancing air quality."

Benefit Cost Evaluation

State DOTs, MPOs and other local transportation agencies can use benefit cost evaluation to determine whether to implement traffic signal timing programs and projects. Benefit-cost analysis can inform decision-makers as to where the best locations to improve signal timing and the most cost-effective alternatives to employ. There is a variety of pre-developed tools available to conduct benefit cost evaluation. Users can also conduct benefit-cost analysis using their own custom spreadsheets or models.  TOPS-BC, an FHWA developed spreadsheet-based tool, is one option. TOPS-BC also has a function designed to aid users in identifying additional tools.

The following presents the methodology and results of using TOPS-BC for a deployment of preset signal timing.  While based on actual deployment information, this case study produces hypothetical results. The purpose of this example is to highlight how TOPS-BC can be deployed to evaluate similar strategies. 

TOPS-BC Data Inputs

TOPS-BC provides input defaults for most variables that a planner would use in the evaluation of a signal-timing project.  If a planner was looking at a system similar to this signal-timing project example, he could use the TOPS-BC defaults, or generate new data to make the example as realistic as possible by applying local data, which the TOPS-BC user can apply in place of the defaults.  This also allows the TOPS-BC user to test the impact of changes in selected input data.  For example, the TOPS-BC user can perform the analysis for examples that highlight local or recent information for their project using different technology costs, traffic levels, wait times, etc.

Table 9 provides a listing of the required input cost variables to run TOPS-BC for a preset traffic signal coordination project. TOPS-BC supplies many of the required inputs to run the model as shown in the final column of Table 9. The user must supply inputs that TOPS-BC does not provide. Each of the items shown in the final column of Table 9 are included in the default input data set, but may be replaced with user supplied data as shown. If the TOPS-BC user enters user-supplied data, it will override the default value and TOPS-BC will use that data in all calculations that call for that input data.

Table 9. Input Variables & User-Supplied Cost Data for Preset Traffic Signal Coordination.
Required Input Variables User Supplied Data Inputs TOPS-BC Supplied Inputs
Basic Infrastructure Equipment
Year of Deployment 2013
Number of Infrastructure Deployments 1
Linked Signal System LAN - Useful Life 20
Linked Signal System LAN - Capital / Replacement Costs (Total) $55,000
Linked Signal System LAN - O&M Costs (Annual) $1,100
Incremental Deployment Equipment (per Intersection)
Number of Incremental Deployments 29
Signal Controller - Useful Life 15
Signal Controller - Capital / Replacement Costs (Total) $6,250
Signal Controller - O&M Costs (Annual) $350
Communication Line - Useful Life 20
Communication Line - Capital / Replacement Costs (Total) $750
Communication Line - O&M Costs (Annual) $6,600
Facility Characteristics
Length of Analysis Period (Hours)   3
Number of Analysis Periods per Year 500
Link Length (Miles) 2.8
Total Number of Lanes 4
Link Capacity (All Lanes - for the time period of analysis) 270,001
Free Flow Speed (MPH)  40 45
Facility Performance
Link Volume (during the time period of analysis)  21,120
Impacts Due To Strategy
Change in Capacity (%) 12%
Change in Speed (%) 0%
Change in # of Lanes 0%
Reduction in Crash Rate (%) 2%
Reduction in Crash Duration (%) 0%
Reduction in Fuel Use (%) 5%
1 Capacity is calculated as 4 lanes for 3 hours at 2250 v/l/h. Lane capacities per hour from the Highway Capacity Manual (HCM).
Note: For a detailed discussion of TOPS-BC data input procedures and options, see the TOPS-BC Manual at: http://plan4operations.dot.gov/topsbctool/index.htm

Model Run Results

Table 10 summarizes the benefits and costs that TOPS-BC calculated. The table shows total annual costs of $218,571. Additional detail in the TOPS-BC model provides information on costs by year as well as total net present value costs. According to TOPS-BC, the first year costs were $404,550 with continuing annual cost for the 20-year analysis period of $201,550. This results in a 20-year net present value of just over $1.76 million.

Table 10. Benefit Cost Summary.
Category Value
Annual Benefits
Travel Time $1,174,801
Travel Time Reliability $0
Energy $317,436
Safety $1,724
Other $0
User Entered $0
Total Annual Benefits $1,493,326
Annual Costs
Total Annual Costs $218,571
Benefit-Cost Comparison
Net Benefit $1,274,755
Benefit-Cost Ratio 6.83

Since the deployment on Alameda Avenue is already complete, the local agency could enter the actual cost experience. TOPS-BC provides some cost defaults, but users are encouraged to review these values and make changes based on local data. Users may also wish to disaggregate costs by lower level traffic signal subsystem as was done in Case Study 5-2.

Benefits

TOPS-BC estimates benefits from the preset signal timing deployment from travel time savings, change in travel time reliability, reduced energy consumption and reduced crash events. Together they result in annual benefits of about $1.5 million. These benefits are in the range of benefits shown in Table 10 which range from $600 thousand to $6.2 million per project.

In this case, TOPS-BC estimates that the project benefits far exceed the costs by a ratio of 7 to 1. This positive result accrues from a gain in operating efficiency for the arterial system reducing travel time and fuel consumption. Prior to introducing the arterial signal coordination, insufficient capacity during the morning and evening peak traffic periods led to congestion and lost time for road users. With the introduction of improved traffic signal timing, traffic flows were smoother reducing stops and delays, and improving travel times. TOPS-BC also estimated a substantial reduction in energy (fuel consumption) costs due to congestion relief. The number of crashes was also estimated to decline slightly, providing an added cost reduction benefit.

Key Observations

This case examines how users can employ TOPS-BC to evaluate the benefits and costs of a traffic signal coordination project. Colorado's Alameda Avenue project provides some of the data to illustrate how a user can run TOPS-BC. By conducting post deployment BCA, DRCOG and CDOT built up a data base of signal control costs and benefits that could inform the decision process for future deployment consideration.

Case Study 5.2 – Adaptive Traffic Signal Control in Greeley and Woodland Park, Colorado

Strategy Type: Arterial Operations
Project Name: Adaptive Traffic Signal Control in Greeley and Woodland Park, Colorado
Project Agency: Colorado DOT
Location: Greeley and Woodland Park, Colorado
Geographic Extent: One 4.00 mile and one 3.65 Mile Corridor
Tool Used: Custom In-house Analysis

Note: Chapters 2, 3, and 4 of this Compendium contain a discussion of the fundamentals of benefit-cost analyses (BCA) and an introduction to BCA modeling tools.  These sections also contain additional BCA references.

Project Technology or Strategy

Adaptive signal control systems coordinate control of traffic signals across a signal network, adjusting the lengths of signal phases and other parameters based on prevailing traffic conditions.  This innovative technology uses real-time data collected by system detectors to optimize signal timing for each intersection in the corridor.  The use of real-time data means that signal timing along the corridor changes to accommodate the traffic patterns at any given time of the day.  There are many different adaptive traffic signal control systems.

Project Goals and Objectives

The City of Greeley implemented adaptive traffic signal control systems on 10th Street (US 34 Business) in Greeley and US 24 in Woodland Park.  The Colorado DOT (CDOT) selected two alternative systems, System A and System B, for implementation.  CDOT commissioned a study to summarize the evaluation results of the two systems.  The purpose of the study was to summarize the results of the evaluation conducted regarding the implementation of two different adaptive traffic signal control systems in Colorado: the System A system on 10th Street (US 34 Business) in Greeley and the System B on US 24 in Woodland Park.  The intent of the evaluation was not to make a recommendation for a specific system, but to report a comparison of the two systems, the requirements for installation and operations, and the benefits obtained from each system.  This would allow decision makers and others interested in this innovative technology to make informed decisions regarding the installation of such a system on other highways and roadways within their jurisdictions
The primary goal of this effort was to reduce congestion, smooth traffic flows, improve travel times, maximize the benefits of signal timing, and potentially reduce crashes.  Thus adaptive traffic signal control can be viewed as a way to delay the need for more costly improvements such as adding capacity to the corridor.

Data

The study collected data on before and after conditions and costs in order to conduct a benefit-cost analysis.

Before and After Conditions

The study evaluated corridor operations for both before and after conditions.  Table 11 shows the results of the before and after travel time runs for the two corridors for both weekday and weekend traffic conditions.  The percentages represent the combined improvement for travel times for a total of six runs through the corridor in each direction of travel during six time-periods for a weekday and one time-period for the weekends.

Table 11. Travel Time Study Results: Measure of Effectiveness Benefit (Percentage Change)
Study Period  Corridor  Travel Time  Stopped Delay  Average Speed 
Overall Weekday 10th Street -9% -13% 11%
Overall Weekday US 24 -6% -15% 7%
Overall Weekend 10th Street -11% -37% 13%
Overall Weekend US 24 -19% -54% 22%
Source: Colorado DOT

Installation Costs

The study also calculated the actual costs that the agencies had to spend to install the new systems. Table 12 shows the costs associated with the installation of the systems, based on information provided by each agency. Implementing the System A adaptive control system on 10th Street cost approximately $905,500, while the System B system cost about $176,300.

Both of the systems installed required the agencies to spend additional funds to upgrade the existing signal system equipment in order to accommodate new system or operational needs. On 10th Street, several of the existing controller cabinets were not large enough to accommodate the new equipment and some of the intersections were in need of a new conduit to accommodate the wiring of new video detection cameras and their associated repeater devices. In addition, the installation required a communication system in order to ensure the controllers at each intersection could communicate with each other. It is possible that a corridor could have System A installed without the need to spend funds on any improvements, which would have saved almost $500,000 of the total $905,000 spent to install the system. On US 24, approximately $13,100 of the system installation costs was for new controllers to ensure the ability to run the firmware necessary to operate System B. Again, it is possible that this expense would not be necessary on another corridor, which would have reduced the overall cost of the project.

Table 12. Cost to Implement the Adaptive Signal Control Systems
Item  Cost
System A Adaptive Control on 10th Street
Misc.  Construction (sidewalk, potholing, erosion, etc.) $34,750
Bored Conduit $6,600
Pull Boxes $7,100
Wiring $35,510
System A System and Components $416,319
Install Controller Cabinets $10,125
Telemetry (communication system) $38,178
Construction equipment and control $101,418
Engineering $250,000
Annual Maintenance Costs (estimate) $5,500
TOTAL  $905,500
System B Adaptive Control on US 24
Central Control System $30,750
10 -Local Controller Firmware $36,000
Training $3,000
Central/Local Software Install and Configuration $3,300
Misc.  Install Costs $1,800
Support from Contractor $8,500
Controller, HC11 $13,120
16 -Microwave Presence Detectors $66,550
Misc.  Cables/Tape/DSL Line/Computer $1,580
CDOT Labor to Install (160 hours at $37.50 per hour) $6,000
Annual Maintenance Costs $4,500
TOTAL  $176,300

The study included additional analysis to compare how much would have been spent maintaining and retiming the existing signal systems compared to how much the agencies expected to spend maintaining the new systems. One main assumption for maintaining the existing systems is the need to retime the signals every five years or approximately four times in the next 20 years.

Benefit Cost Evaluation

The benefit-cost analysis determined the payback period for each system, as well as the benefits that CDOT, the City of Greeley, but more importantly the general public and roadway users would realize in the future. Table 13 provides the factors the study used to calculate benefits and costs.

Table 13. Benefit and Cost Categories.
Benefits Costs
  • Travel time
  • Fuel consumption
  • Side-street delay
  • Design and engineering cost
  • Adaptive system cost
  • Detection/communication upgrade cost
  • Construction/installation cost
  • Staff time spent for design, installation, and training
  • Expected annual maintenance

The local agencies directly provided the cost data. The following sections describe the calculation of each of the benefit categories.

Calculation of Benefits

Travel Time: The analysis multiplied total travel time (vehicle-hours) by the value of time and vehicle occupancy values for the area to calculate the cost savings in terms of reduced travel time.

Fuel Consumption: The analysis multiplied total travel time (vehicle-hours) by fuel consumption rates and the average per gallon fuel cost for the area.

Side-Street Delay: The analysis used the Highway Capacity Manual method for field measurement of intersection control delay to calculate intersection control delay and LOS.

Travel Time. The value of travel time is calculated as:

Equation. The value of travel time saved equals the change in travel time multiplied by the value of time multiplied by vehicle occupancy.
Figure 13. Equation. The Value of Travel Time.

Where:

ΔTT is the change in Travel Time
VT is the Value of Time
VO is Vehicle Occupancy
VTT is Value of Travel Time Saved

The value of time for both corridors was obtained from research performed by FHWA and input from the CDOT Division of Transportation Development (DTD) staff and was found to be $15.00 per person per hour. CDOT staff indicated a recent study for the area identified the average vehicle occupancy for both of the highways is 1.3 people per vehicle. Annual costs and benefits were computed based upon a 350 day year (250 weekdays and 100 weekend days) to best capture the majority of typical traffic volume days. The remaining days of the year were considered non-typical travel days (holidays, events, weather, etc.) and were omitted from the computation.

Fuel Consumption. Fuel consumption is calculated as:

Total Travel Time (vehicle-hours)* Fuel Consumption Rate * Average Price
Figure 14. Equation. Fuel Consumption.

Internet research identified average fuel costs of $3.65 per gallon in the Greeley area and $3.50 in the Woodland Park area. Current fleet average fuel consumption rates at various speeds are available from EPA.

Side-Street Delay. For a signal control project with fixed cycle lengths during specific periods of the day, traffic simulation software can estimate side-street delay at study intersections. Because the adaptive traffic signal systems are continuously changing signal timing parameters to react to real-time travel demand, the analysis used the Highway Capacity Manual method for field measurement of intersection control delay to calculate intersection control delay and level of service (LOS). Video recordings were conducted at four intersections on each corridor, as identified by agency staff, to capture the before and after conditions during the morning, midday, and evening weekday peaks.

Summary of Benefits

Table 14 provides the benefits of implementing the adaptive signal control systems. The systems result in significant savings to both corridors, with 10th Street experiencing a predicted annual user savings of more than $1.326 million dollars per year and US 24 users experiencing an annual savings of almost $900,000 per year.

Table 14. Benefits of Implementing the Adaptive Signal Control Systems.
Measure of Effectiveness Daily Benefit Value of Daily Benefit
(veh*hrs or gal)
Annual benefit1 (millions)
System A Adaptive Control on 10th Street
Travel Time (veh*hrs) 207 $4,034 $1.41
Fuel Consumption (gal) 122 $445 $0.16
Side-street delay -41 ($805) ($0.28)
Annual Maintenance (estimated by staff to be a 130 hours saving per year at $35 per hour) $115 $0.04
TOTAL $3,789 $1.33
System B Adaptive Control on US 24
Travel Time (veh*hrs) 191 $3,730 $1.31
Fuel Consumption (gal) 149 $522 $0.18
Side-street delay -87 ($1,698) ($0.59)
Annual Maintenance (estimated by staff to be a 130 hours saving per year at $35 per hour) $12.86 $0.01
TOTAL $2,567 $0.90
1 Assumes benefits realized for 350 days.
Source: Colorado DOT

Model Run Results

A consultant, using a standalone custom in-house analysis, conducted the benefit-cost analysis. Table 15 provides various metrics of benefits, costs, and savings that the consultant team calculated. Overall, benefit-cost ratios vary from 1.58 to 6.10 for the first year that the systems are in operation. Based on the analysis, Region 4 and the City of Greeley will accrue benefits of approximately $8.9 million over the first 20 years with System A managing the traffic operations on the 10th Street corridor. At the same time, Region 2 will accrue benefits of about $5.8 million over the first 20 years with System B managing the traffic operations on the US 24 corridor.

Table 15. Summary of the Results of the Benefit-Cost Analysis.
Category System A System B
Actual Project Minimal Project Actual Project Minimal Project
Number of Intersections 11 8
Daily cost saving (corridor) $3,789 $2,567
Annual cost saving (corridor) $1.326 million $898,500
Install costs (corridor) $905,500 $375,000 $176,300 $162,400
Daily cost saving (per intersection) $344 $321
Annual cost saving (per intersection) $120,500 $112,300
Install costs (per intersection) $82,300 $34,000 $22,000 $20,300
Benefit to cost ratio 1.58 3.79 5.64 6.1
10-year projected savings $4.2 million $4.7 million $2.8 million $2.8 million
20-year projected savings $9.2 million $9.7 million $5.7 million $5.7 million
Note: Actual projects had unusual costs; minimal project represents the expected costs for other projects.
Source: Colorado DOT

Key Observations

This case evaluates the introduction of adaptive traffic signal control systems on two arterials. Adaptive signal control systems coordinate traffic signals across a network, adjusting the signal timing parameters based on prevailing traffic conditions. Prior to and after the deployment, the study collected data on performance to be able to compare the changes brought about by the deployment. The data collection revealed improvements in terms of travel time, fuel consumption and side street delay. The study also collected data on implementation costs and estimated implementation cost savings for specific costs that would not be necessary on another corridor. The analysis illustrates how benefit-cost analysis can be used to compare alternative adaptive traffic signal systems. It also informs decision makers and others interested in this innovative technology to make informed choices regarding the installation of such a system on other highways and roadways within their jurisdictions.

Case Study 5.3 – Adaptive Traffic Signal Control

Strategy Type: Arterial Operations
Project Name: Adaptive Traffic Signal Control
Project Agency: State DOT Based on Colorado DOT Experience
Location: Urban Area
Geographic Extent: Corridor
Tool Used: Custom In-house Analysis

Note: Chapters 2, 3, and 4 of this Compendium contain a discussion of the fundamentals of benefit-cost analyses (BCA) and an introduction to BCA modeling tools. These sections also contain additional BCA references.

Project Technology or Strategy

Adaptive signal control systems coordinate control of traffic signals across a signal network, adjusting the lengths of signal phases based on prevailing traffic conditions. This innovative technology uses real-time data collected by system detectors to optimize signal timing for each intersection in the corridor. The use of real-time data means that signal timing along the corridor changes to accommodate the traffic patterns at any given time of the day.

Project Goals and Objectives

A State DOT commissioned the evaluation of an adaptive traffic signal control system on a principal arterial. The goal of the traffic signal control project was to reduce congestion, smooth traffic flows, improve travel times, maximize the benefits of signal timing, and potentially reduce crashes, which delay the need for more costly improvements such as adding capacity to the corridor.

The corridor primarily serves local traffic, including commuters, during the week and visitors and recreational travelers on the weekends. The traffic patterns can vary rapidly and unpredictably on the weekend due to the nature of recreational travelers and weather conditions that may cause travelers to change when they begin and terminate their recreational activities. Thus, the current application of time-of-day based signal coordination plan were identified as inadequately adjusting to the travel patterns of the visitors that come to and pass through the area.

Data

The commissioned report described the changes that were required to install and operate the adaptive signal control system, including costs for installation and maintenance, and provide a comparison of before and after implementation measures of effectiveness (MOE) to quantify the benefits to traffic operations within the study area. The study collected data on before and after conditions and costs in order to conduct a benefit-cost analysis.

Before and After Conditions. The study evaluated corridor operations for both before and after conditions. The study evaluated the following MOEs for the corridor:

  • Travel time.
  • Fuel consumption and emissions.
  • Intersection delay and level of service (LOS).
  • Average number of stops.

Calculation of Benefits

Travel Time: The analysis multiplied total travel time (vehicle-hours) by the value of time and vehicle occupancy values for the area to calculate the cost savings in terms of reduced travel time.

Fuel Consumption: The analysis multiplied total travel time (vehicle-hours) by fuel consumption rates and the average per gallon fuel cost for the area.

Side-Street Delay: The analysis used the Highway Capacity Manual method for field measurement of intersection control delay to calculate intersection control delay and LOS.

Installation Costs. The study calculated the actual costs that the agencies had to spend to install the new systems. The study also conducted additional analysis to compare how much would have to be spent maintaining and retiming the existing signal systems compared to how much the agencies expected to spend maintaining the new systems. One main assumption for maintaining the existing systems was the need to retime the signals every five years or approximately four times in the next 20 years.

Benefit Cost Evaluation

The purpose of the benefit cost evaluation was to summarize the results of the evaluation conducted regarding the implementation of the adaptive traffic signal control system.

Approach. The benefit-cost analysis determined the payback period for each system, as well as the benefits that the State DOT and local agencies, and more importantly the general public and roadway users, would realize in the future. Table 16 provides the factors the study used to calculate benefits and costs.

Table 16. Benefit and Cost Categories for Adaptive Traffic Signal Control.
Benefits Costs
  • Travel time
  • Fuel consumption
  • Side-street delay reduction
  • Design and engineering cost
  • Adaptive system cost
  • Detection/communication upgrade cost
  • Construction/installation cost
  • Staff time spent for design, installation, and training
  • Expected annual maintenance

The local agencies directly provided the cost data. The following sections describe the calculation of each of the benefit categories.

Travel Time. The analysis multiplied total travel time (vehicle-hours) by the value of time and vehicle occupancy values for the area to calculate the cost savings in terms of reduced travel time. The study obtained the value of time from research performed by FHWA and input from the State DOT staff and was found to be $15.00 per person per hour. A recent study for the area identified the average vehicle occupancy for the highway was 1.3 people per vehicle. Annual costs and benefits were computed based upon a 350 day year (250 weekdays and 100 weekend days) to best capture the majority of typical traffic volume days.

Fuel Consumption. The analysis multiplied total travel time (vehicle-hours) by fuel consumption rates and the average per gallon fuel cost for the area. Internet research identified average fuel costs.

Side-Street Delay. For a signal-timing project with fixed cycle lengths during specific periods of the day, traffic simulation software can estimate side-street delay at study intersections. Because the adaptive traffic signal systems are constantly changing cycle lengths to react to real-time travel demand, the analysis used the Highway Capacity Manual method for field measurement of intersection control delay to calculate intersection control delay and LOS. Video recordings were conducted at four intersections, to capture the before and after conditions during the morning, midday, and evening weekday peaks.

Model Run Results

A consultant, using a standalone custom in-house analysis, conducted the benefit-cost analysis. The consultant reported that, based on the benefits and cost to install the new system, the system implementation will:

  • Result in a benefit to cost ratio for the first year of operation of 5.64, which means for every $1 spent installing the system the Region will experience a cost saving of $5.64 per dollar invested on the corridor.
  • Provide a daily saving of $2,567 in terms of reduced delay and fuel consumption.
  • Pay for itself in approximately 67 days, or 2.2 months, after the system is initially installed and made operational, which means the system had already paid for itself during the time this evaluation was being completed.
  • Save the region and the road users more than $5.7 million over the first 20 years that the system is in operation.

Table 17 provides a summary of the results of the benefit-cost analysis.

Table 17. Summary of the Results of the Benefit-Cost Analysis for Adaptive Traffic Signal Control.
Category  Finding/Result
Number of Intersections 8
Daily cost saving (corridor) $2,567
Annual cost saving (corridor) $898,500
Install costs (corridor) $176,300
Daily cost saving (per intersection) $321
Annual cost saving (per intersection) $112,300
Install costs (per intersection) $22,000
Benefit to cost ratio 5.64
10-year projected savings $2.8 million
20-year projected savings $5.7 million

Key Observations

This case identifies the evaluation of an adaptive traffic signal control systems on an arterial. Adaptive signal control systems coordinate control of traffic signals across a signal network, adjusting the lengths of signal phases based on prevailing traffic conditions. Prior to and after the deployment, the study collected data on performance to be able to compare the changes brought about by the deployment. The data collection revealed improvements in terms of travel time, fuel consumption and side street delay. The study also collected data on implementation costs and conducted a benefit-cost analysis. The benefit-cost analysis did not properly frame the costs and benefits in relation to the alternatives and did not incorporate net present values of the streams of benefits and costs over the project life. The analysis illustrates how the use of a model such as TOPS-BC can structure the analysis to insure the analysis avoids common mistakes and produces meaningful results.

Case Study 5.4 – Hypothetical Roundabouts

Strategy Type: Arterial Operations
Project Name: Hypothetical Roundabouts
Project Agency: Washington State DOT
Location:  Urban Setting
Geographic Extent:  Urban/Suburban Arterials
Tool Used:  TOPS-BC

Note: Chapters 2, 3, and 4 of this Compendium contain a discussion of the fundamentals of benefit-cost analyses (BCA) and an introduction to BCA modeling tools. These sections also contain additional BCA references.

Project Technology or Strategy

Modern roundabouts are a type of intersection characterized by a generally circular shape, yield control on entry, and geometric features that create a low-speed environment. Modern roundabouts provide a number of safety, operational, and other benefits when compared to other types of intersections. On projects that construct new or improved intersections, planners should examine the modern roundabout as an alternative.

In the planning process for a new or improved intersection where a traffic signal is under consideration, a modern roundabout should likewise receive serious consideration as an alternative. This begins with understanding the site characteristics and determining a preliminary configuration. There are a number of locations where roundabouts are advantageous and a number of situations that may adversely affect their feasibility. As with any decision regarding intersection treatments, planners should take care to understand the particular benefits and trade-offs for each project site.

Project Goals and Objectives

The Washington State DOT's (WSDOT) website includes a page devoted to Roundabout Benefits (http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm). On that page, WSDOT states, "Studies have shown that roundabouts are safer than traditional stop sign or signal-controlled intersections." The WSDOT webpage also notes that roundabouts reduce delay and improve traffic flow. The webpage states, "Contrary to many peoples' perceptions, roundabouts actually move traffic through an intersection more quickly, and with less congestion on approaching roads. Roundabouts promote a continuous flow of traffic. Unlike intersections with traffic signals, drivers don't have to wait for a green light at a roundabout to get through the intersection. Traffic is not required to stop – only yield – so the intersection can handle more traffic in the same amount of time." Finally, the WSDOT webpage also notes that roundabouts are less expensive than traffic signals. The webpage states, "The cost difference between building a roundabout and a traffic signal is comparable. Where long-term costs are considered, roundabouts eliminate hardware, maintenance and electrical costs associated with traffic signals, which can cost between $5,000 and $10,000 per year."

Given these advantages, planners and traffic engineers may want to estimate the benefits of conversion of a signalized intersection to a roundabout. These practitioners can readily use TOPS-BC to perform such calculations at the sketch planning level.

Data

Note: The data used in this Case Study is used for illustrative purposes and not intended to suggest expected performance benefits from roundabouts. The next Case, Case 5-5, shows different operational and safety performance data assumed in Maryland.

The WSDOT webpage cites a study by the Insurance Institute for Highway Safety (IIHS) that estimates that roundabouts reduced injury crashes by 75 percent at intersections that achieved traffic control through stop signs or signals. Figure 15, reprinted from the WSDOT webpage and based on studies by the IIHS and Federal Highway Administration, shows that roundabouts may achieve:

  • Thirty-seven percent reduction in overall collisions.
  • Seventy-five percent reduction in injury collisions.
  • Ninety percent reduction in fatality collisions.
  • Forty percent reduction in pedestrian collisions.
Chart indicates that installing roundabouts results in a 37 percent reduction in overall collisions, 75 percent reduction in injury collisions, a 90 percent reduction in fatality collisions, and a 40 percent reduction in pedestrian collisions. Source: Federal Highway Administration and Insurance Institute for Highway Safety (FHWA and IHS).
Figure 15. Graph. Reduction in Collisions for Roundabouts.

The WSDOT webpage cites studies by Kansas State University (http://www.ksu.edu/roundabouts/) that measured traffic flow at intersections before and after conversion to roundabouts. In each case, installing a roundabout led to a 20 percent reduction in delays.

Benefit Cost Evaluation

State DOTs, MPOs and other local transportation agencies can use benefit cost evaluation to aid in determining whether to implement an intersection project such as a roundabout. There is a variety of pre-developed tools available to conduct benefit cost evaluation. Users can also conduct benefit-cost analysis using their own custom spreadsheets or models. TOPS-BC, an FHWA developed spreadsheet-based tool, is one option. TOPS-BC also has a function designed to aid users in identifying additional tools.

TOPS-BC

TOPS-BC provides input defaults for most variables that a planner would use in the evaluation of a project. While TOPS-BC does not provide defaults for roundabouts, the user could still use TOPS-BC by adding a new strategy to the benefit estimation capability.

TOPS-BC Data Inputs. This hypothetical TOPS-BC case assumes that the initial costs of adding a signalized intersection and a roundabout are comparable and is just interested in the magnitude of benefits.

User-supplied Performance Data

  • Vehicle Hours of Travel: 132 hours of vehicle travel.
  • Number of Fatality Crashes: Multiply the baseline value by 10 percent.
  • Number of Injury Crashes: Multiply the baseline value by 25 percent.
  • Number of Property Damage Only Crashes: Multiply the baseline value by 63 percent.
  • Fuel Consumption (Gallons): Multiply Vehicle Hours of Travel by the ratio of Fuel Consumption to Vehicle Hours of Travel (132*241.4797/132.5834=240.4171).

The user has several options for creating a new strategy in TOPS-BC. These include:

  • The user may carefully review and consider the various strategies that are available, and select one to copy (or rename) that most closely resembles the analysis capabilities desired for the new strategy.
  • The user may create a new strategy from the Generic Link Model worksheet that contains many common analysis methodologies for link based analyses.

This case assumes that the user has chosen the first option and will simply rename the strategy. Since the user is evaluating a roundabout, which is an arterial intersection project, the case assumes the user selected the "Arterial Strategy" "Signal Coordination." Figure 16 shows a partial view of the Signal Coordination Model sheet with the strategy renamed to "Roundabout."

Screen capture shows a partial view of the Signal Coordination Model sheet with the strategy renamed to "Roundabout." The sheet contains data on facility characteristics and facility performance. Source: Federal Highway Administration TOPS-BC
Figure 16. Screenshot. A Run for Roundabout Benefits Using the Tool for Operations Benefit-Cost Analysis.

User and TOPS-BC Supplied Site Data. Entering user-supplied data allows the TOPS-BC user to make the analysis as specific as possible for their project. This case assumes the TOPS-BC user has some specific site characteristics including Length of Analysis Period (3-hour peak-period), Link Length (one-mile), and Total Number of Lanes (one lane) and Link Volume (5,400 vehicles per period). As congestion exists in both directions during the peak, this case assumes the user sets the Number of Analysis Periods per Year to 500. None of these values override the values for which TOPS-BC provides a default value, such as Link Capacity (5,400 vehicles per period) or Free Flow Speed, for which TOPS-BC provides a value of 45 miles per hour.

User Supplied Performance Data. This case assumes that the TOPS-BC user enters specific data on the performance of roundabouts. TOPS-BC uses five performance characteristics in calculating the benefits. These performance characteristics, along with the user-entered values include:

  1. Vehicle Hours of Travel. The WSDOT webpage provides an estimate of a 20 percent reduction in delay. If 5,400 vehicles traveled one mile at 45 miles per hour this would result in 120 hours of vehicle travel (5,400*60/45/60=120). However, TOPS-BC assumes this volume would cause average speed to drop to 40 mph resulting in 135 hours of vehicle travel (5,400*60/40/60=135), resulting in 15 hours of vehicle delay (135-120=15). If the user applies the 20 percent reduction in delay to the 15 hours of vehicle delay, this results in a reduction of delay of 3 hours (15*20%=3) and a new estimate of 132 hours of vehicle travel (135-3=132) with a roundabout in place. The case assumes the user enters the new estimate of 132 hours of vehicle travel in the Improvement Override field for Vehicle Hours of Travel.
  2. Number of Fatality Crashes. The WSDOT webpage provides an estimate of a 90 percent reduction in fatality collisions. This case assumes the user enters a formula in the Improvement Override field for Number of Fatality Crashes that multiplies the Baseline Value by 10 percent (0.1), as only 10 percent of fatality collisions occur with a roundabout in place.
  3. Number of Injury Crashes. The WSDOT webpage provides an estimate of a 75 percent reduction in injury collisions. This case assumes the user enters a formula in the Improvement Override field for Number of Injury Crashes that multiplies the Baseline Value by 25 percent (0.25), as only 25 percent of injury collisions crashes occur with a roundabout in place.
  4. Number of Property Damage Only Crashes. The WSDOT webpage does not provide an estimate reduction in Property Damage Only Crashes. However, the webpage does provide an estimate of a 37 percent reduction in overall collisions. This case assumes the user enters a formula in the Improvement Override field for Number of Property Damage Only Crashes that multiplies the Baseline Value by 63 percent (0.63), as only 63 percent of all collisions occur with a roundabout in place.
  5. Fuel Consumption (Gallons). The WSDOT webpage does not provide an estimate reduction in fuel consumption. This case assumes the user enters a formula in the Improvement Override field for Fuel Consumption that multiplies Improvement Override field for Vehicle Hours of Travel by the ratio of Fuel Consumption to Vehicle Hours of Travel field for the Improvement Column (132*241.4797/132.5834=240.4171). This assumes that the reduction in fuel consumption follows a ratio of fuel consumption to vehicle hours of travel that is similar to the ratio obtained through signal coordination.
  6. Default Economic Parameters. In addition to the characteristics that describe the project such as technology specific costs, roadway descriptions, number of installations, etc., the TOPS-BC user may also want to input values different from the TOPS-BC defaults for economic parameters related to the measures of benefits for the project. Examples include the value of time or reliability, the price of fuel, the cost of crashes or dollar value of other benefits the TOPS-BC user may have calculated such as vehicle emissions. This case assumes that the user has left all of these parameters unchanged.

Model Run Results

TOPS-BC estimates the annual benefits of the roundabout resulting from travel time savings, change in travel time reliability, reduced energy consumption and reduced crash events. Table 18 provides each of these benefits as TOPS-BC calculates and shows them on the "My Deployments" page. Together they result in annual benefits of $76,020.

Table 18. Benefit Summary.
Category Annual Benefits
Travel Time $45,591
Travel Time Reliability $0
Energy $25,272
Safety $5,158
Other $0
User Entered $0
Total Annual Benefits $76,020

With the introduction of a roundabout, rather than a traditional signalized intersection, traffic flows are smoother, reducing stops and delays, and improving travel times. TOPS-BC estimates a substantial reduction in travel times resulting in substantial travel time benefits. This reduction in stops and delays also reduces energy (fuel consumption) costs. Due to low travel speeds (drivers slow down and yield to traffic before entering a roundabout), no light to beat (roundabouts promote a continuous circular flow of traffic), and one-way travel (roundabouts direct drivers counterclockwise and eliminate the possibility for T-bone and head-on collisions) the number of crashes also declined, providing a safety benefit due to crash cost reduction.

Key Observations

This case examines how users can employ TOPS-BC to evaluate the benefits of a roundabout project. Washington State DOT's roundabouts webpage provides some of the data as an example of what a user might consider to run TOPS-BC. The TOPS-BC run estimates that the project would generate annual benefits of $65,204. This example illustrates how the user can add new strategies to TOPS-BC and use data from real world projects. In this case we also used information and methods contained in TOPS-BC on fuel savings from adaptive signal control projects to estimate fuel savings from roundabout installation. This is an approximation of the fuel savings from roundabouts. If consideration of roundabouts continued beyond this preliminary review, the analyst might consider developing better estimates of roundabout fuel savings.

Case Study 5.5 – Effectiveness of Roundabouts in Maryland

Strategy Type: Arterial Operations
Project Name: Effectiveness of Roundabouts in Maryland
Project Agency: Maryland Department of Transportation
Location:  Urban and Rural
Geographic Extent:  Statewide
Tool Used:  Custom Stand Alone BCA Model Focused on Safety Benefits

Note: Chapters 2, 3, and 4 of this Compendium contain a discussion of the fundamentals of benefit-cost analyses (BCA) and an introduction to BCA modeling tools. These sections also contain additional BCA references.

Project Technology or Strategy

Modern roundabouts are a type of intersection characterized by a generally circular shape, yield control on entry, and geometric features that create a low-speed environment. Modern roundabouts provide a number of safety, operational, and other benefits when compared to other types of intersections. On projects that construct new or improved intersections, planners should examine the modern roundabout as an alternative. Figure 17 provides a diagram illustrating the key characteristics of a modern roundabout.

The key characteristics of a roundabout include the option to have more than one lane, a generally circular shape, a counter-clockwise rotation, no need to change lanes to exit, yield signs at entry points, geometric and physical features that force slow speeds. Source: Maryland DOT
Figure 17. Diagram. Key Roundabout Characteristics.

In the planning process for a new or improved intersection where a traffic signal or stop control is under consideration, a modern roundabout should likewise receive serious consideration as an alternative. This begins with understanding the site characteristics and determining a preliminary configuration. There are a number of locations where roundabouts are advantageous and a number of situations that may adversely affect their feasibility. As with any decision regarding intersection treatments, planners should take care to understand the particular benefits and trade-offs for each project site.


Calculations are based on the anticipated accident experience expected to occur had no roundabouts been installed compared to the actual after period accident experience.

Project Goals and Objectives

The State of Maryland published a report that evaluates the effectiveness of roundabouts in Maryland. Studies have found that one of the benefits of roundabout installations is the improvement of overall safety performance. The calculations in the report are based on the anticipated accident experience expected to occur had no roundabouts been installed compared to the actual accident experience at the roundabout locations. The state has found that single-lane roundabouts perform better than two-way, all-way stop and signalized intersections. Although the frequency of crashes is not always lower at roundabouts, particularly multi-lane roundabouts, injury rates are lower.

Data

The Maryland analysis indicates that at the 15 locations where Maryland has installed single lane roundabouts there has been a 68 percent decrease in the total accident rate per million vehicles entering the intersection (mve). In addition, there was a 100 percent decrease in the fatal accident rate/mve, an 86 percent reduction in the injury accident rate/mve, and a 41 percent reduction in the property damage only accident rate/mve. Figure 18 provides before and after graphical comparisons of the total and injury-only accident rates.

Chart shows that the total accident rate during the before period was 2.35, but dropped to 0.76 in the after period. The injury accident rate during the before period was 1.34 and dropped to 0.19 in the after period.
Source: Maryland DOT
Figure 18. Graph. Before and After Total and Injury Accident Rates.

The accident data is from the Maryland State Highway Administration (MDSHA) accident database. This database consists of all accidents for which the state received an official accident report form from the Maryland Automatic Accident Reporting System (MAARS). The study collected accident data for 15 single-lane mini roundabouts. The before and after period vary depending on completion dates of the roundabouts.

Maryland reports that the initial total cost of the roundabouts was $6,219,505. The state assumes the projects have a 15-year service life. The state assumes there is no before and after annual operating and maintenance cost or salvage value for these projects.

Benefit Cost Evaluation

The Maryland study utilized both the cost-effectiveness and the benefit cost techniques. The cost-effectiveness method determines the cost of preventing a single accident to decide whether the project cost was justified. This technique does not price benefits. Instead, the method determines the cost of reducing accidents by severity.

An alternate method is the benefit cost technique. The benefit-cost analysis compares the Annual Benefit (AB) to the Equivalent Uniform Annual Cost (EUAC) over the entire service life of the roundabouts. Maryland considers any project that has a benefit-cost ratio greater than 1.0 to be economically successful. Use of this method requires that the dollar value is placed on all cost and benefit elements related to the project. Maryland has developed its own average accident cost figures, stratified by severity.

Model Run Results

The Maryland State Highway Administration's Traffic Safety Analysis Division, using a stand-alone custom in house analysis, conducted the cost-effectiveness analysis and benefit-cost analysis. This analysis used Maryland's own accident cost figures by severity, which reports the average cost of a fatal accident at $4,167,062, the average injury accident cost at $110,584, and average property damage only accident cost at $26,156.

Maryland's objective in conducting the cost-effectiveness evaluation was to determine the amount of dollars spent to reduce one accident.

Equation. The levelized annual cost for the roundabout program in Maryland equals the total cost for the roundabout program in Maryland times the capital recovery factor. A notation below indicates that the levelized annual cost for the roundabout program in Maryland divided by the number of accidents avoided equals TAC divided by the number of accidents avoided.
Figure 19. Equation. Dollars Spent to Reduce One Accident.

Where:

AC = Levelized Annual Cost for Roundabout Program in Maryland
TC = Total Cost for Roundabout Program in Maryland
CRF = Capital Recovery Factor, assumes 6 percent interest rate and a 15 year project life
Acc = Number of accidents avoided
Table 19. Calculation of Cost per Accident Avoided by Roundabout Program in Maryland.
Data Definition Estimated Value
Total Cost of Roundabout Program in Maryland $6,219,505
Capital Recover Factor, 6% Interest & 15 Year Life 0.103
Average Annual Cost (Levelized) $640,609
Number of Accidents Avoided by 15 Roundabouts 49
Total Cost per Accident Avoided $13,146
Estimated Average Cost of Non-fatal Accident $200,000
Source: Maryland DOT

MDSHA estimated the annual benefit of crash avoidance by using the crash frequency and costs by crash type prior to the roundabout installation to estimate the expected crash frequency and costs after installation. The expected crashes without the roundabouts were compared to the actual crash results for a 4.5 year period after deployment. This resulted in an annual savings of $9.8m. For more detail on the MDOT benefit calculations, see the report referenced at the end of this case.


Equivalent Uniform Annual Cost (EUAU)

Equivalent Uniform Annual Cost is the "payment" required to fund the Life Cycle Cost over the service life. It is calculated as:

Equation. Equivalent uniform annual cost equals the annualized program cost (comma) the annual interest rate (comma)  the service life in years.
Figure 20. Equation. Equivalent Uniform Annual Cost.

Where:

A/P = Annualized program cost ($/sq. ft.)
i = annual interest rate (%)
n = service life (years)

Unlike the cost effectiveness evaluation, which determines how many dollars the state must spend to reduce one accident, the benefit-cost analysis considers the initial cost of the projects for the entire service life (15-years) of the roundabouts. The Maryland BCA converts initial cost into an EUAC, also referred to as levelized cost. The analysis then divides the EUAC into the AB to reveal the BCR. The Maryland analysis does this to calculate the amount of money spent over the 15-year service life for roundabout installations as opposed to just calculating the dollar value realized through the annual safety benefits in accident prevention. The analysis indicates that for every dollar spent on the roundabout installation over the entire 15-year service life, the state anticipates that the roundabout users will realize approximately $15 in benefits through accident reduction. This calculation is:

Annual benefits divided by annual cost equals the benefit cost ratio.
Figure 21. Equation. Benefit-Cost Ratio.


Table 20. Benefit-Cost Ratio for Roundabout Program in Maryland.
Data Definition Estimated Value
Annual Crash Avoidance Benefit (AB) $9,810,219
Equivalent Uniform Annual Cost (AC) $640,609
Benefit-Cost Ratio (BCR) 15.3
Source: Maryland DOT

Key Observations

This case presents the results of an economic evaluation of roundabouts conducted by Maryland State Highway Administration's Traffic Safety Analysis Division, Office of Traffic & Safety. The calculations are based on the anticipated accident experience had no roundabouts been installed, compared to the actual after period accident experience. The state found that single-lane roundabouts perform better than two-way, all-way stop and signalized intersections. The state utilized both the cost-effectiveness and the benefit cost techniques.

The analysis illustrates how both cost-effectiveness and benefit-cost analysis can be useful to compare alternatives to operational strategies. It informs decision makers and allows others interested in this technology to make informed choices regarding the installation of such a system on roadways within their jurisdictions.

Cost-effectiveness (CE) and BCA are related and may both be appropriate ways for a decision maker to evaluate a potential deployment. For example, CE is better suited to situations when alternatives are expected to provide equal outcomes (benefits), so that the differentiator between alternatives is cost. BCA is more comprehensive, considering costs and benefits of alternative projects and project designs that may provide different levels and timing of both costs and benefits.

Case Study 5.6 – Effectiveness of Arterial Management in Florida

Strategy Type: Arterial Operations
Project Name: Effectiveness of Arterial Management in Florida
Project Agency: Florida Department of Transportation
Location:  Urban
Geographic Extent:  Arterial Corridor
Tool Used:  TOPS-BC

Note: Chapters 2, 3, and 4 of this Compendium contain a discussion of the fundamentals of benefit-cost analyses (BCA) and an introduction to BCA modeling tools. These sections also contain additional BCA references.

Project Technology or Strategy

The following case study was prepared by Cambridge Systematics, Inc. for the Florida Department of Transportation (FDOT) as part of the "TOPS-BC Florida Guidebook" and is reproduced here with permission.

FDOT District 4 in collaboration with Palm Beach County Traffic Engineering Department (PBC TED) initiated the "Living Lab" pilot project in 2012 to actively monitor, manage, and improve arterial operations along three major east-west corridors – Okeechobee Boulevard, Belvedere Road, and Southern Boulevard between SR 7 and I-95.

Project Goals and Objectives

As part of this initiative, FDOT District 4 installed several CCTV cameras and BlueTOAD vehicle detection devices along these corridors to monitor traffic conditions and collect travel times in real-time. In addition, FDOT District 4 provided staffing resources at the Palm Beach County Traffic Management Center to monitor real-time traffic conditions, detect incidents, and support Palm Beach County Signal Timing staff in implementing real-time signal timing changes to improve traffic flow and reduce motorist delay.

FDOT District 4 Freeway Intelligent Transportation Systems (ITS) staff and Palm Beach County Signal Timing Engineers work together to improve freeway-arterial coordination during incidents on I-95 in Palm Beach County. The hours of operation are Monday through Friday from 7a.m. to 7p.m. Figures 22 and 23 show the location of the Living Lab and device locations along the instrumented roadways.

Screen capture of a page that provides maps of the areas covered, lists the locations of the major arterials within the coverage area as well as their AADTs, and sums up the total project miles and the numbers of CCTVs, BlueTOADs, and signals.
Source: Florida DOT
Figure 22. Screenshot. Palm Beach Living Lab Coverage.

A location map depicting the locations of existing and planned CCTVs and BlueToad devices.
Source: Florida DOT
Figure 23. Screenshot. Palm Beach Living Lab Device Locations.

Assumptions

There were many assumptions that went into the TOPS-BC analysis for the Palm Beach Living Lab case study. Also, several limitations should be noted. These are listed in the following sections.

Costs

Costs for implementing and operating the Living Lab project were provided by the PBC TED. The cost of equipment and devices installed in the study area (along with operations and maintenance costs) were assigned to the Incremental Deployment cost. Several costs were also provided by PBC TED that are used to manage the entire countywide traffic control system, i.e. TMC operators, incident management software, ATMS.now license, and INRIX data subscription. These costs were assigned to the basic infrastructure costs because they are needed to operate the countywide traffic signal system with or without the Living Lab project.

Benefits

It is not possible to analyze more than one corridor at a time using TOPS-BC. For this case study, a separate TOPS-BC spreadsheet was set up for each of the six primary corridors in the study area. A process to determine an overall BC ratio for the Living Lab program is described later in this section.

Link volume data was obtained from intersection counts conducted periodically by the PBC TED. The volumes are part of a countywide traffic count program and were counted on a rotating basis between 2010 and 2013. The link volume used in the calculation was determined by averaging the approach volumes of each intersection available in the intersection count program for the corridor (considering the east/west approaches on Okeechobee, Belvedere and Southern and the north/south approaches on Military, Jog and SR 7) and using the highest average volume as the volume in the spreadsheet. An example of the volumes for Okeechobee Blvd. is shown in Table 21. The volumes in the count program are defined by approach, EA is the east approach or westbound. The peak volume is the p.m. peak hour in the east approach (westbound).

Table 21. Okeechobee Boulevard Volume Counts.
Road Intersection AM NA AM SA AM EA AM WA PM NA PM SA PM EA PM WA
Okeechobee Blvd  at I-95 0 1497 2667 2141 0 1730 3082 2474
Okeechobee Blvd  at Australian Avenue grade separated
Okeechobee Blvd  at Congress Avenue 581 556 1825 1775 695 665 2182 2123
Okeechobee Blvd  at Military Trail 1257 1251 2172 2110 1468 1461 2536 2464
Okeechobee Blvd  at Haverhill Road 851 754 2104 2138 960 850 2373 2412
Okeechobee Blvd  at Jog Road 1169 1196 2249 2261 1216 1245 2341 2354
Okeechobee Blvd  at Sansbury's Way 139 311 2148 1974 147 329 2277 2092
Okeechobee Blvd  at SR 7 805 1513 1909 1668 1296 2437 3074 2687
Sum Total - - - 15074 14068 - - 17866 16606
Average - - - 2153 2009 - - 2552 2372
Source: Florida DOT
EA= east approach • NA = north approach • SA = south approach • WA = west approach

The highest total volume is the sum of the east approaches. The average peak approach one hour volume is 2552. Each of the other corridor volume inputs was determined in this manner.

Speeds were also obtained from the PBC TED. The FDOT Systems Planning Office standard for free flow speed is the speed limit plus 5 miles per hour (mph). The speed limit varies in sections of the corridors between 35 and 50 mph. The free flow speed should then be between 40 and 55 mph. In this case study PBC TED provided data that allowed the free flow speed to be determined by averaging off-peak travel times along each corridor using the Bluetooth detectors and calculating the average speed over several months. The baseline speed is based on historic travel time data collected prior to the implementation of the Living Lab project. The Baseline Override speed shown is the speed for the peak hour and direction of the highest volume, in the Okeechobee case above the speed used in the spreadsheet is for the PM EA approach. The Improvement Override speed was collected after implementation of the Living Lab project by PBC TED using the Bluetooth detectors and reported in the PBC TMC Active Arterial Management Program Performance Measures Monthly Report. The speeds used were from the November 2013 report.

The number of analysis periods is different from for the I-95 Express Lanes case study. The benefits are accrued for the peak hour in the peak direction, which is represented by 250 analysis periods, which are the average number of work days in a year (total days minus weekends and holidays). However, while the p.m. peak hour was found to have the highest volumes, significant benefits are also accrued for the a.m. peak hour. In a case where the a.m. peak hour has the highest volumes, the p.m. peak hour should be included in the same manner. In order to account for those benefits the peak volume in the a.m. peak period was identified and a ratio of that volume to the highest peak hour volume was determined. That portion of the 250 analysis periods was added to the 250 original analysis periods. (Another option is to conduct two separate BCA analyses, one for each direction.) Using the Okeechobee example in Table 21, the corresponding peak period is the a.m. peak hour. The east approach was the highest volume approach in the a.m. period so that volume (2153) was used. The a.m. peak to p.m. peak hour volume ratio is 2153/2552 or 0.844. The a.m. peak should account for 84.4 percent of the amount of analysis periods that the p.m. peak hour provides, so 250 X .844 is 211; 211 + 250 is 461. The amount of benefits accrued in both the a.m. and p.m. peak hours is accounted for by using 461 analysis periods. The other corridors' benefits were calculated in the same manner. This methodology provides a conservative estimate of benefits since only two peak hours of benefits are accounted. Volumes for periods other than the peak hour were not available.

National average (default) input data was used for crashes, fuel consumption, and the value of time. This was due to the difficulty in collecting and summarizing data or the fact that data were not available at all.

Limitations. While TOPS-BC does include the benefits due to time savings in recurring and non-recurring travel during each analysis period, the impacts of improvements due to improved travel time reliability are included only in freeway analysis. Reliability has been recognized as an important consideration to travelers. Improving reliability is a benefit to travelers. The SHRP 2 research project dedicated a significant portion of its resources to defining, understanding and measuring reliability. SHRP 2 has released several reports relating to the topic. Not all of this research has been added to the TOPS-BC model Version 1. TOPS-BC V1 now estimates only the benefits from reducing incident related delay. In the future, TOPS-BC will add new code to address the current reliability benefits and add these benefits to the full BCA. The latest model will be available on the FHWA Planning for Operations web site (http://www.ops.fhwa.dot.gov/plan4ops/index.htm).

TOPS-BC does not have a trip assignment or mode choice module, therefore the operations strategy analysis only accounts for the number of trips given for each corridor, there are no trip diversions or mode changes due to congestion.

TOPS-BC will provide conservative estimates of benefits because only the benefits accrued during the selected time period are calculated.

In many cases, additional benefits may be produced in off-peak times that are not included.

Changes in air quality due the operations strategies are not accounted for in TOPS-BC.

Methodology

The following are the steps to enter input data for the Palm Beach Living Lab case study. Note that separate TOPS-BC calculations are required for each of the six corridors in the study area. The steps are the same for each corridor but the input volumes and speeds are different.

Costs.

  1. Click on Traffic Signal Coordination Systems – Central Control under Section 3 – Estimate Costs.
  2. The incremental deployment costs are entered in each item row, both for capital/replacement cost and for operations and maintenance costs. Each item cost is the cost per intersection multiplied by the number of intersections. The signal controller cost includes the cost of any in-pavement presence loops.
  3. The basic infrastructure costs are not included in the benefit-cost calculation, as this case is considering only the benefits of the incremental improvement by the Living Lab project.
  4. Each item is assigned a useful life. The project life cycle is 20 years, so there are no replacement costs for the traffic signal and communications lines. There is one replacement assumed for the cameras and detectors. The useful life is entered for each cost item.
  5. The annualized total project cost is then calculated by the spreadsheet as an output.
  6. The total cost for the incremental deployment was determined and each corridor was assigned a percentage of the total project cost based on the ratio of the traffic signals along that corridor to the total number of traffic signals in the study area. Using Okeechobee as an example, there are 23 traffic signals in the Okeechobee corridor, which is 29.1 percent of the total 79 traffic signals in the study area. Therefore, Okeechobee was assigned 29.1 percent of the project cost. Using the total cost will account for the deployment in both directions even though the benefits are accrued for one direction in the peak hour. This will provide a conservative estimate of the B/C ratio.
  7. The calculated costs of each corridor are then added back together to obtain a total project B/C ratio.

See Figure 24 for a screenshot of the Costs page for the Okeechobee Blvd. corridor in this case study.

Screen capture of the costs page for the Okeechobee Blvd. corridor traffic signal coordination system. Costs listed include those for basic infrastructure equipment and incremental deployment equipment.
Source: FHWA TOPS-BC
Figure 24. Screenshot. Tool for Operations Benefit-Cost Analysis Traffic Signal Coordination Systems Costs Page.

Benefits. The Okeechobee Blvd corridor will be used as an example for providing input data to the spreadsheet.

  • Click on Signal Coordination under Section 4 - Estimate Benefits. Input data into the Facility Characteristics section.
  • Enter one into the Length of Analysis Period green box because the traffic volume data is for a one hour period
  • Select Central Control for the Signal Timing Type, the Living Lab project provided central control in the study area.
  • Select Principal Arterial for the Link Facility Type since the corridors are principal arterials.
  • Enter 8 in the Link Length, which is the length of the east/west corridors.
  • Enter 4 in the Total Number of Lanes, which is the number of basic lanes in each direction in most segments along the corridor.
  • TOPS-BC will calculate the roadway capacity as an output.
  • Enter 41.5 into the Free Flow Speed green box, that speed was provided by PBC TED based on analysis of off-peak travel times using Bluetooth readers. The speed limit should not be used as the free flow speed arterials, it will not account for traffic stopping at signals. The correct method to obtain free flow speed is to measure travel time over the length of the corridor in uncongested times of day and divide by the corridor length.
  • In the Facility Performance section, enter 2552 into the Link Volume green box, which was provided PBC TED as described above.
  • Enter 26.0 into the Congested Speed, Baseline Override box, which the p.m. peak hour speed collected by PBC TED prior to implementation of the Living Lab project.
  • Enter 29.6 into the Congested Speed, Improvement Override box, which is the most current corridor p.m. peak hour speed reported by PBC TED in their monthly performance measures report.
  • Enter 461 into the Number of Analysis Periods per Year box, which accounts both the p.m. and the a.m. peak hours per year as described in the Assumptions section above.
  • As an output TOPS-BC will calculate the annual benefits to the corridor. For Okeechobee Blvd. the annual benefits were found to be $1,419,813.

See Figures 25 and 26 for screenshots of the Benefits page for the Okeechobee Blvd. corridor in this case study.

Screen capture of part of the benefits page for the Florida case study. The page depicts values for specified facility characteristics, such as link length, number of lanes, etc., as well as facility performance characteristics, such as link volume, number of crashes by type, congested speed, etc.
Source: FHWA TOPS-BC
Figure 25. Screenshot. Tool for Operations Benefit-Cost Analysis Traffic Signal Coordination Systems Benefits Page (part 1).
Screen capture for part of the benefits page that includes the value of the impacts due to selected strategy, as well as improvements in travel time, energy, and safety.
Source: FHWA TOPS-BC
Figure 26. Screenshot. Tool for Operations Benefit-Cost Analysis Traffic Signal Coordination Systems Benefits Page (part 2).

Preliminary Benefit Cost Evaluation

Based on the six corridors benefits and costs calculations using the TOPS-BC spreadsheet, the results are shown in Table 22.

Table 22. Benefits and Costs for the Palm Beach Living Laboratory Case Study.
Corridor Peak Time/Direction Benefits Cost B/C Ratio
Southern Blvd  AM EB $2,179,220 $149,454 14.58
Belvedere Road PM WB $1,270,182 $133,330 9.53
Okeechobee Blvd PM WB $1,419,812 $180,460 7.87
Military Trail PM NB $972,212 $47,130 20.63
Jog Road PM NB $235,011 $55,192 4.26
SR 7  PM NB $159,651 $55,192 2.89
Total System  n/a $6,236,088 $620,758 10.05
Source: Florida DOT
B/C = benefit/cost

Key Observations

After conducting these and other TOPS-BC case studies and applications, several "lessons learned" have been identified.  There are also a few hints to setting up the spreadsheet that will help TOPS-BC users achieve better results.

  • Speed is the most important factor affecting the benefits of an operations strategy.  A difference in "before" and "after" speed is the primary way to account for congestion and delay and improvement benefits in TOPS-BC.  In the Palm Beach Living Lab case study, before and after speed was the only way to account for the operations of the traffic signal system along the corridor, it is the overall travel time (converted to speed) that accounts for the stop delay in a corridor.  The number of traffic signals is not part of the calculation.  It is relatively easy to collect current travel times using GPS travel time runs or Bluetooth detectors.  However, it is more difficult to obtain historic corridor speeds for project already implemented or to estimate speeds for a project being planned.  When actual historic data is not available, it is best to consult with the local MPO and obtain model speeds for the corridor.
  • The free flow speed is important because it is the goal from which travel time savings potential is measured.  The FDOT Planning Office free flow speed is the posted speed limit plus 5 mph.  When conducting operations analysis and when historic data is available the free flow may be determined from collected data.  For freeways, the average off-peak (uncongested) speed collected over time from detectors is the calculated free flow speed.  For arterials the stop time at traffic signals must be accounted for, so the operations method of determining free flow speed is to average off-peak corridor travel times over time, as was done in the Palm Beach case study.  When conducting planning studies the speed limit plus 5 mph should be used as the free flow speed.
  • Volume and volume/capacity ratio are also important factors in TOPS-BC calculations.  The current volume is the only volume input, however, when needed (such as an intersection improvement) the capacity can be overridden for both the baseline and the improvement scenarios.  Volume and V/C are used to calculate vehicle miles traveled and crash rates and affect the benefits calculation.
  • The period of analysis must be correct in order to obtain accurate results.  The number of hours of the analysis must match the length of the period of the volume data, that is, if the volumes are for a peak one hour, the period of analysis must be one. 
  • The number of analysis periods per year can be used to account for additional benefits not measured directly by data input.  In the Palm Beach case study, the number of analysis periods was increased to account for the other peak hour of the day.  The ratio of the a.m.  peak hour to the p.m.  peak hour was multiplied by the number of workday peak hours per year (250) to account for the benefits of both peak hours.  Additional hours of benefits could have been added in the same manner if the volumes were known.  Another option would be to conduct two BCA, one for each direction.
  • For the cost calculations, there are several important considerations.  The costs of providing basic services – services that would be provided whether or not the project being studied was implemented – and the cost of the incremental services enabled by the project must be sorted out and correctly assigned.  Each cost item should have a corresponding operations and maintenance cost entered in the spreadsheet. 
  • It is also important to match the cost of a project to the benefits being calculated.  For example, in the Palm Beach case study the cost of the project in a corridor was halved in the B/C calculation because the benefits were only calculated for one direction along that corridor. 
  • The user must be careful to pay close attention to the units that are assumed in the spreadsheet cells; i.e., be sure to determine if the model is assuming a daily rate vs. an annual rate for a factor.
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