12.2.3 Computational Steps ICE Stage 2 and Subsequent Analyses
This section discusses software used for roundabout analysis in Stage 2 ICE and for subsequent purposes related to design refinement. It includes a basic overview of different software packages, basic input parameters, typical output parameters, and additional external guidance that can be used during analysis. The tools mentioned in this section represent common software used in roundabout analysis, but do not represent all software options that can be used in roundabout analysis. Several different software can be used for roundabout analysis. See
Appendix M, Section 2
for a more detailed scription of each analysis software package. The selection of software depends on the project type and needs. In addition, when results from one analysis software are on the boundary of indicating a need for additional lanes, use of more than one analysis software is recommended. A summary of commonly used roundabout analysis tools is shown in Tool | Type | When to use | Notes | Outputs |
|---|---|---|---|---|
Highway Capacity Software (HCM 7th Edition) | Deterministic | After CAP-X and planning-level analysis of number of lanes. Use peak hour volumes | Apply software default values for headway and capacity parameters If V/C results > 0.85 use Junctions | V/C, Control delay and LOS, 95% queue lengths by approach |
SIDRA Intersection | Deterministic | After CAP-X and planning-level analysis of number of lanes. Use peak hour volumes | Use US HCM model and default HCM headway parameters | V/C ratio, control delay, LOS, 95% queue length |
Synchro | Deterministic | After CAP-X and planning-level analysis of number of lanes. Use peak hour volumes | Use software default HCM gap parameters | V/C ratio, control delay, LOS, 95% queue length |
Junctions ( Assessment of Roundabout Capacity and Delay (ARCADY)) | Deterministic | After computational steps are complete and more detail is necessary. For analyzing more than two lanes. | Analyze both the US HCM model and the ARCADY model to create a range of results. Calibrate the Y-Intercept by -10% for build-year conditions analysis and -5% for design year analysis. | V/C ratio, control delay, LOS, 95% queue length |
Vissim | Microsimulation | For oversaturated conditions; closely spaced signals and/or roundabouts; complex roadway geometry; or when a visual representation is necessary | Can be accompanied by a deterministic tool (SIDRA, Synchro, or Junctions). Use default headway values | Delay and average network travel time |
Synchro/ SimTraffic | Microsimulation | For oversaturated conditions; closely spaced signals and/or roundabouts; complex roadway geometry; or when a visual representation is necessary | Can be accompanied by a deterministic tool (HCM, SIDRA, Synchro, or Junctions). Use default headway values | Delay and average network travel time |