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

Traffic Analysis Toolbox Volume X:
Localized Bottleneck Congestion Analysis
Focusing on What Analysis Tools Are Available, Necessary and
Productive for Localized Congestion Remediation

Appendix A. Tool Selection Worksheet

Freeway

Depending on the needs of the project, modeling a freeway might require having field data on car-following and lane-changing behavior, but in most cases, default values from the tools should suffice. Some projects might require intense network coding, depending on the study area size and complexity. Table A.1 summarizes the characteristics of different tool types under multiple criteria.

Arterial

Depending on the needs of the project, modeling an arterial may need to include transit operations. Table A.2 summarizes the characteristics of different tool types under multiple criteria.

Roundabout

Depending on the needs of the project, modeling a roundabout might require modeling conflicting volumes. Some projects might include interaction intersections, isolated intersections, or both. Some projects demand comparing geometric configurations. Browse below (Table A.3) to find the category of tool that best fits your specific project.

Signalized Intersections

Depending on the needs of the project, modeling a signalized intersection might require pedestrian behavior. Some projects might transit signal priority, while others might not. Browse below (Table A.4) to find the category of tool that best fits your specific project.

Table A.1 Freeway Characteristics of Different Tool Types under Multiple Criteria

Freeway Characteristics of Different Tool Types under Multiple Criteria
Characteristic Equation Deterministic Macroscopic Microscopic Mesoscopic
Level of detail Only for analyzing broad criteria based on theoretical capacity constraints; only geometric component is number of lanes and grade. Only for analyzing broad criteria based on geometric capacity constraints; geometry used as physical capacity limits. Regional travel demand patterns. Vehicle Interactions, detailed geometry and operational elements (i.e., ramp meters, HOT lanes) may be modeled. Limited Vehicle Interactions, detailed geometry and operational elements modeled.
Calibration effort None. Minor - Not many driver or roadway characteristics to change. Medium - No calibration needed unless analyst must use innovative techniques to mimic some nonsimulatable strategies. Significant - Localized bottlenecks can be represented in great detail, so traffic counts, travel times, and bottleneck extents need to be calibrated. Significant - Localized bottlenecks can be represented as aggregate delay functions that represent slow down; average speed of vehicle groups/link performance must be calibrated.
Methodology Static equations. Capacity-based standard equations. Speed/density relationships and localized volume/ratios are utilized. Vehicle-to-vehicle interactions and interactions with geometry modeled. Vehicle interactions usually modeled based on average speed density relationships of vehicle groups or links.
Recommended Application Capacity determination. Preliminary feasibility studies. Regional TDM analysis. Detailed and accurate representation of bottlenecks; reconstruction/construction staging, alternative analysis, diversion analysis. Series of localized bottlenecks and possible diversion.
Dynamic traffic assignment None. None. None. Available. Available.

Ease of use

 High. High. Medium. Low. Low.
Graphical representation Basic diagrams. Moving vehicles with geometric constraints. Link volumes only. Detailed geometry, vehicle movements, and dynamic performance measures. Detailed geometry, limited vehicle details, and aggregated dynamic performance measures.
Input data requirements Easy to find inputs. Counts, overlays (design files or aerial photos). Counts, geographic information layers. Counts, aerials/design files, travel times, and bottleneck details. Counts, aerials/design files, travel times, and bottleneck details.
Weaving and merging Theoretical capacity estimates. Physical/geometric capacity constrained. Volume/capacity representation only. Represented through vehicle interactions and geometry modeling. Represented through aggregated speed density relationships.
Sight distance requirements Theoretical estimates independent of freeway characteristic, demand, or design. None. None. None. None.
Performance measures LOS, capacity, estimated delay. Volumes, speeds, LOS, capacity, estimated delay. Volumes, LOS. Volumes, LOS, delay, and speeds. Volumes, LOS, delay, and speeds.

Table A.2 Arterial Characteristics of Different Tool Types under Multiple Criteria

Arterial Characteristics of Different Tool Types under Multiple Criteria
Characteristic Equations Deterministic Macroscopic Micoscopic Mesoscopic
Levelof detail Only for analyzing broad LOS criteria based on theoretical capacity constraints.  Only geometric component usable is number of lanes and grade. Only for analyzing broad LOS criteria and delay estimates based on operational systems, such as traffic signals, stop signs, and lanes. Low level of detail due to large coverage areas. Detailed. Only for analyzing broad LOS criteria based on theoretical capacity constraints.  Only geometric component usable is number of lanes and grade.
Calibration effort None. Volume-based calibration. Volume-based for large study areas, but cannot be used for specific location calibration. Significant - Localized bottlenecks can be represented in great detail, so traffic counts, travel times, and bottleneck extents need to be calibrated. Significant - Localized bottlenecks can be represented as aggregate delay functions that represent slow down; average speed of vehicle groups/link performance must be calibrated.
On-street parking As standard capacity reduction. As standard capacity reduction. As standard capacity reduction. As standard capacity reduction. As standard capacity reduction.
Vehicle interaction with pedestrians None. None. As standard capacity reduction. As standard capacity reduction. As standard capacity reduction.
Road markings Number of lanes. Number of lanes with rough geometry. No markings - Only capacity constrained by number of lanes. Number of lanes. Number of lanes.
Transit None. Only operational characteristics such as signal preemption. Some tools have the capabilities. Some tools have the capabilities. Some tools have the capabilities.
Lane restrictions As capacity constraints. Yes. Yes. Yes. Yes.
Traffic signal operations Only standard delay. Detailed timing plans can be modeled. Detailed timing plans can be modeled. Detailed timing plans can be modeled. Detailed timing plans can be modeled.
Traffic density Capacity-based only. Based on broad volume capacity relationships. Can be shown over time. Can be shown over time. Can be shown over time.
Individual travel time None. Low utility of individual travel times. Tracked on a segment-by-segment basis. Tracked individually. Tracked individually.
Delay Capacity-based estimates. Based on operational elements like signals, speed limits, etc. Based on operational elements like signals, speed limits, etc. Based on operational elements like signals, speed limits, etc. Based on operational elements like signals, speed limits, etc.
Graphical representation Diagrammatic representation. Fairly detailed geometric representation. Detailed. Detailed; animations available. Detailed; animations available.
Input data requirements Counts, configuration. Counts, signal timings, traffic, restrictions. Counts, signal timings, traffic, restrictions. Counts, signal timings, transit schedules, traffic, restrictions. Counts, signal timings, transit schedules, traffic, restrictions.
Vehicle categories Represented as Passenger Car Equivalents (PCEs). Represented as PCEs. Classification based on vehicle type, although vehicle dynamics cannot be modeled. Classification based on vehicle type. Classification based on vehicle type.
Intersection right-of-way None. None. Can be modeled. Can be modeled. Can be modeled.

Table A.3 Roundabout Characteristics of Different Tool Types under Multiple Criteria

Roundabout Characteristics of Different Tool Types under Multiple Criteria
Characteristics Equations Deterministic Macroscopic Microscopic
Level of detail Only for analyzing broad LOS criteria based on theoretical capacity constraints.  Not always sensitive to all geometric constraints. Only for analyzing broad LOS criteria based on theoretical capacity constraints.  Geometric components typically used include number of lanes, dimensions of the access points and the circulatory roadways, and grade. No known tools with roundabout capabilities. Vehicle operations and geometry modeled.
Range Single location. Single location. Not Applicable Multiple locations; in series or separate.
Methodology Gap acceptance models* Utilizes linear or exponential empirical regression models based on circulating and entry flows, geometric characteristics, and sometimes driver behavior.** Vehicle-to-vehicle interactions and interactions with geometry modeled.
Performance measures Capacity, delay, and queuing estimation. Capacity, delay, and queuing estimation. Travel time, VHT/VMT, and animations.
Conflicting volumes Calculates conflicting flow rates or circulating flow rates as a function of turning movement volumes. Calculates conflicting flow rates or circulating flow rates as a function of turning movement volumes. Calculates conflicting flow rates or circulating flow rates as a function of turning movement volumes.
Ease of use Easy. Easy. Complex, labor-intensive.
Lane characteristics Single lane only. Number of lanes and lane widths are inputs. Details can be coded into network.
Number of approach legs Not sensitive to geometric parameters. Serve as inputs; more emphasis on entry flows than number of entry/access points. No limits; details can be coded into network.
Angle of approach legs Not sensitive to geometric parameters Sensitive to entry angle and radius - serve as inputs to calculation No restrictions, details can be coded into network
Study area size Only analyzes performance of individual approaches to single roundabout; no multiple roundabout interactions Certain software can analyze multiple roundabout interactions or roundabout interactions with other intersections of various control types. Can analyze multiple roundabout interactions or roundabout interactions with other intersections of various control types.

*"Roundabouts in the United States," NCHRP Report 572, Transportation Research Board, National Academies, 2007.
**Appendixes to NCHRP Report 572: Roundabouts in the United States, Transportation Research Board, National Academies, 2007.

Table A.4 Signalized Intersections Characteristics of Different Tool Types under Multiple Criteria

Signalized Intersections Characteristics of Different Tool Types under Multiple Criteria
Characteristics Equations Deterministic Macroscopic Microscopic Mesoscopic
Level of detail Only for analyzing LOS based on capacity constraints. Only needs number of lanes and grade. Only for analyzing LOS based on capacity constraints. Only needs number of lanes and grade. Uses geometric and volume information as inputs; common outputs are LOS, delay, and queue length. Needs volume, trip distribution, and geometrics as inputs; common outputs are travel time, VHT/VMT, and delay. Needs volume, trip distribution, and geometrics as inputs; common outputs are travel time, VHT/VMT, and delay.
Signal type Pretimed. Pretimed and actuated. Pretimed, actuated, and coordinated. Pretimed and actuated. Pretimed and actuated.
Signal optimization None. None. Available. None. None.
Intersection type Isolated intersection with four legs maximum. Basic operations only. Isolated intersection, with four legs maximum. Basic operations only. Can be in isolated, in series, or grid system. Can be in isolated, in series, or grid system. Can be in isolated, in series, or grid system.
Performance measures LOS, capacity, and delay. LOS, capacity, lane-by-lane volumes, timing, queue lengths, delay, stops, average speed, and throughput. LOS, capacity, lane-by-lane volumes, timing, queue lengths, delay, stops, average speed, and throughput. Throughput, travel time, and delay. Throughput, travel time, and delay.
Roadway conditions Number of lanes, grade, timing. Number of lanes, grade, and timing. Number of lanes, grade, timing, pedestrian, transit, parking factors. Number of lanes, grade, timing. Number of lanes, grade, timing.
Multicycle modeling None. None. Available. Available. Available.
Methodology LOS assessment for signalized intersections based on delay caused by the signal.* LOS assessment for signalized intersections based on delay caused by the signal. LOS assessment for signalized intersections based on delay caused by the signal. Vehicle-by-vehicle simulation, and then aggregated together. Vehicle-by-vehicle simulation, and then aggregated together.
Pedestrian behavior Can estimate the LOS for pedestrians at signalized intersections. Can estimate the LOS for pedestrians at signalized intersections. Can estimate the LOS for pedestrians at signalized intersections. None. None.
Transit signal priority None. None. Basic settings available. Available with custom programming. Available with custom programming.
Unusual geometry Not supported. Not supported. Allowed. Allowed. Allowed.
Graphical representation Simple diagram of three- to four-way intersections. Simple diagram of three- to four-way intersections. Moderate details; no vehicles shown. Detailed; vehicles may be shown. Detailed; vehicles may be shown.
Intersection coding Easy. Easy. Moderate; requires some detailed field info. Data and labor intensive. Data and labor intensive.
Lane restrictions Only capacity constraints. Only capacity constraints. Only capacity constraints. May restrict certain vehicle types. May restrict certain vehicle types.

* Draft Working Paper NCHRP Project 3-85-12, Guidance for the Use of Alternative Traffic Analysis Tools for Highway Capacity Analysis, Chapter 16: Signalized Intersections, University of Florida Transportation Research Center, December 2007.