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

Traffic Analysis Toolbox Volume V:
Traffic Analysis Toolbox Case Studies – Benefits and Applications

5.0 Operational Assessments

Traffic analysis tools that can answer detailed operational questions should be in the toolbox of any practitioner who needs to get the most capacity and performance out of the existing system. The answers these tools provide can guide the engineer and system owner toward effective solutions where expensive and significant changes to the system are just not possible. They do this by answering the detailed questions that usually control individual operational decisions: what signal phasing strategy will maximize capacity and minimize queuing? How is a tolling/inspection station best operated to maximize its throughput? Can an arterial signal system promote transit ridership and still meet the needs of other road users? What can be done to increase average travel speeds in an entire surface street network without building new roads or making any major physical improvements? A complete range of proven and fully-tested tools has been developed; which one to use in any particular situation depends on the characteristics of the problem. The table below presents four case studies that show how some of these tools were used in real-world situations to improve performance and quality of service without the need for significant new infrastructure investments.

Type of Analysis Real-World Case Study
5.1 Sketch Planning Interchange Analysis
Eugene, Oregon
5.2 HCM/Analytical Models Queuing Analysis
Ft. Hood, Texas
5.3 Simulation Models Transit Signal Priority Evaluation
Portland, Oregon
5.4 Traffic Optimization Signal Timing Plan
Ft. Myers, Florida

5.1 Sketch Planning Case Study – Interchange Analysis

A sketch planning traffic analysis tool can be an effective way to resolve signal timing issues at interchanges. This type of tool does not need an extensive amount of input data, and can be used to quickly and effectively evaluate such things as phase sequencing, number of approach lanes, and lane configuration at the signalized intersections.

Coburg Interchange – Eugene, OR

Key Benefits

  • Quickly identified the reason for long queues and the range of possible solutions
  • Used data that is readily available and easy to collect
  • Reduced analysis time by 50-70% compared to a standard operational analysis procedure

Other Considerations

  • This type of traffic analysis tool provides an overall assessment of intersection operation (under-, near-, or over-capacity), but does not estimate the intersection level-of-service.
aerial photograph of the study area. It illustrates the existing north-south system of three closely-spaced signalized intersections, plus the proposed new signal located just east of the northern-most signal in that system

Closely spaced signals lead to queue spillback

The proposed new signal needed to be connected and coordinated to the existing signal system without introducing queuing or cycle failures. The sketch planning traffic analysis tool was used to design a phasing plan and lane configuration that achieved this need.

Sketch-planning traffic analysis tools only need data that are almost always readily available: hourly movement volumes, number of approach lanes, and lane control. Even though sketch-planning traffic analysis tools are not detailed enough to use in final design, their output serves as essential input to other traffic analysis tools that can be used for this purpose.

drawing that illustrates critical lane volume analysis. It shows an intersection layout including lane configurations and traffic volumes per lane. It also highlights one of the conflicting movement pairs at the intersection (northbound left-turn and southbound through movement).

Sufficient Data for a Solution

Inspection of traffic volumes at the interchange showed that the existing controller phasing (starting and ending both ramps together) resulted in unnecessary congestion. By eliminating this constraint, the southbound arterial traffic was free to fill the space between the intersections, resulting in more efficient use of the interchange.
bar graph reflecting the analysis time required to assess the interchange capacity needs. The graph indicates that this was accomplished in 10 hours using the sketch planning tool, but otherwise could have taken up to 40 hours if a more detail-intensive tool was employed.

Sketch Planning Reduces Staff Time Required

Using sketch planning traffic analysis tools, the Coburg Road intersection analyses were completed in 25-30 percent of the time that would have been required if the traditional traffic analysis tools had been applied, and with results that fully addressed the study needs.

Eliminate Costly Improvements

The intersections along Coburg Road needed to meet minimum volume-to-capacity ratio (v/c) thresholds. Sketch planning traffic analysis tools were able to meet this need. As a result, the need for a $1 million interchange reconfiguration was avoided by a $15,000 signal controller upgrade.

5.2 HCM/Analytical Model – Queuing Analysis

Analytical models can be used in combination with more detailed analysis procedures to provide a robust examination of complex situations. Deterministic tools such as the HCM or other analytical models are effective ways to get answers to some questions like lane control and queue space requirements. Their output is relatively easy to understand and they also provide an efficient way to compare and contrast alternatives.

Security Screening Analysis – Fort Hood, TX

Key Benefits

  • Provided visual confirmation of vehicle ingress and egress characteristics under different lane configurations
  • Confirmed infrastructure needs
  • Demonstrated the need for optimizing checkpoint operations and resources

Other Considerations

  • These models require moderate to detailed amounts of data that sometimes require significant collection effort.
  • Calibration of the models is important to ensure they produce consistent results.
photograph of the roadway leading to the Fort Hood Main Gate

Consistent Evaluation

Changes in security policies required an evaluation of the security checkpoints at the Army base in Fort Hood, Texas. Analyses were completed to optimize checkpoint operations and minimize delays across varying traffic conditions throughout a typical day. The traffic analysis tool provided a consistent frame of reference for the different time periods that were evaluated.

Clear and Consistent Results

The HCM procedure was used to determine an initial estimate for queuing based on military standards for gate processing times for several threat condition levels. Analysis results were presented in an easy-to-understand tabular format that clearly identified the effects of different options on staffing requirements and vehicle delay.

Microsimulation was subsequently used for more detailed analysis of individual scenarios.

The output from the analytical tools can also be used as input to microscopic simulation models capable of a much more detailed analysis. For example, simulation allows visual confirmation of operating characteristics as well as examination of more detailed issues.

Base personnel used the traffic simulation model to support presentations to military officers and other key stakeholders. Ultimately, the simulation model was used to support full, detailed design of access control points.

computer-generated drawing of vehicle processing infrastructure

Effective Use of Several Tools

This project benefited significantly from the sequential application of two different levels of traffic analysis tools. The analytical model provided basic insights into sizing issues such as number of lanes and number of checkpoints. The simulation model provided visual confirmation of operating characteristics and allowed examination of more detailed issues like variable processing times, and the effects of special events or incidents.

Development of Cost Effective Solutions

Using these traffic analysis tools, lane configurations were developed for use in determination of staffing levels by time period. Prior to the analysis, staffing levels were overestimated and resulted in needless costs to the agency.

bar graph of the number of staffed lanes at one gate for a 24-hour period

5.3 Traffic Simulation Model Case Study – Transit Signal Priority Evaluation

Microsimulation was the appropriate tool to evaluate the effects of transit signal priority strategies on traffic flow along major arterial corridors in Portland, Oregon. This is because it was able to predict important performance measures that other analysis tools could not – including, for example, vehicle delay and both on-time performance and travel time variability for various levels of bus service. Its ability to illustrate the effects of alternative control strategies through animation was a very effective way for engineers and decision-makers alike to assess the overall system performance characteristics.

Transit Signal Priority – Portland, OR

Key Benefits

  • Demonstrated how bus travel speed can be increased without significant effects on traffic flow
  • Documented and quantified important operational details (queues, delay, etc.)

Other Considerations

  • Effective use of microsimulation requires investment in data collection and calibration.
photograph of a bus stop at an intersection along one of the arterials studied in Portland, Oregon, to determine the effects of transit priority for signals along the corridor

Designing the system

Microsimulation allowed the system design to be fine-tuned to meet the City of Portland's needs. Bus stop locations, stop service percentage, traffic conditions, and signal timing strategies were varied to isolate the effects of individual elements on the TSP system, and then the system design was adjusted to get the desired outcomes.
aerial view of an intersection near a bus pullout area within the VISSIM micro-simulation environment. The figure represents a graphical snapshot of the animation showing vehicle movements at the intersection and a bus stopped nearby at the pullout for boarding and alighting.

Quantifying key parameters

By tracking the movement of each vehicle individually, microsimulation can give the decision maker a handle on important considerations that other analysis tools cannot – considerations like the amount of travel time variability experienced by transit riders.

Hardware-in-the-loop

Hardware-in-the-loop uses a combination of simulation software and field signal controller equipment to evaluate traffic conditions in an office setting prior to field implementation. Using this technique reduces disruptions for traffic and transit during installation and allows analysis to quantify the effect of specific signal timing strategies or settings.

photograph of four engineers standing in front of an open controller cabinet. One person is pointing to the hardware in the cabinet while discussing how the hardware works. The simulation allows for fine-tuning of the signal priority strategies prior to implementation in the field.

Sufficient assessment of strategies

Use of simulation insured that limitations of the field hardware were addressed and resolved prior to implementation. This approach reduced the amount of staff time in the field required to implement the strategy, resulting in significant cost savings.
photographs of a Controller Interface Device, VISSIM Simulation, and 170 Traffic Controller and their relationships

Effects of variability

Performance of the signal priority system is dependent on the controller settings and transit operations. Reducing travel time variability is a key to improving on-time performance for transit and simulation of elements such as boarding and traffic interaction allowed assessment of key measures that otherwise are difficult to quantify.

5.4 Traffic Optimization Case Study – Signal Timing Plan Development and Implementation

A traffic optimization tool was used when Lee County, Florida undertook the retiming of over 100 signals along 18 arterials, including 20 signals in downtown Fort Myers. The tool was used to develop initial signal timing plans to minimize stops and delays to arterial through traffic. The plans were implemented and then fine-tuned in the field.

Countywide Signal Retiming – Fort Myers, Florida

Key Benefits

  • Efficient way to test multiple scenarios and strategies
  • Improved quality of service to road users

Other Considerations

  • Tool must first be calibrated to field conditions to ensure the development of realistic performance expectations
map of Lee County, Florida, highlighting the corridors and intersections studied in the project

Development of Optimization Strategies

The model was used to assess existing traffic conditions as well as develop new signal timing plan options for each corridor (6-10 plans per corridor).
screen capture of the optimization tool used in this project. The screen capture shows the model representation of one corridor under evaluation including intersection geometries at each intersection.

Testing of Multiple Scenarios

Due to the seasonal fluctuation in travel demand, two sets of final timing plans (peak and off-peak season) had to be developed and implemented for each corridor.

The traffic optimization tool allowed for the testing, evaluation, and refinement of multiple strategies for each scenario prior to field implementation. Visual outputs that are available from this type of tool can be useful to engineers in affirming the correctness of the input as well as in demonstrating the benefits of the new signal timing plans to others.

Benefits Achieved

  • More effective use of engineers' time
  • Average peak-hour delays were reduced by 16% and stops were reduced by 22%.
  • Easier field implementation
bar graph reflecting the time efficiency gained by implementing the optimization tool. The graph shows analysis that would have taken 100 hours of staff time to complete without the optimization tool. By using the tool, the task was accomplished in only 55 hours of staff time.

Efficiencies Gained

Using an optimization tool gained both cost and time efficiencies by providing a means to test and refine strategies, prior to field implementation. This minimized the amount of staff time spent in the field, reduced the amount of staff time required overall, and minimized disruption to traffic flow during the implementation and field refinement process.
photograph of the project field implementation. It shows an engineer inputting a timing plan into a signal controller and observing traffic flow along the adjacent road.

Assistance in Decision Process

The optimization tool helped in making key project decisions by testing and evaluating multiple strategies in an efficient and controlled manner.
time-space diagram for one of the study corridors. From the diagram, one can review traffic progression through a series of traffic signals.

Assistance in Implementation

Field implementation was made easier through the tool's ability to create signal timing worksheets, time-space diagrams, and flow profiles that were then used to develop controller-ready timing plans.
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