Overview
Signals and roundabouts use the planning methods in NCHRP Report 825, Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual (2016). Those sections adapt the Highway Capacity Manual, 6th Edition. Median U-turn (MUT) and restricted crossing U-turn (RCUT) use the planning methods added later in NCHRP Research Report 1087, Guide for Intersection Control Evaluation (2024), Appendix B, from NCHRP Project 17-98.
This is a planning analysis. It is not the full HCM operational procedure, and it is not Cap-X.
Routes
Section titled “Routes”Per-type routes run one scenario. Each type is published as POST /api/v1/signal and POST /api/v1/signal/analyze, and the same pair for roundabout, MUT, and RCUT.
POST /api/v1/calculate repeats that scenario for each supplied hour. sixteenHourEfficiency and sixteenHourExcessCapacity then use analysisWindow (default 5:00–21:00). maxVcRatio and hoursBelowCapacity use every supplied hour.
POST /api/v1/report returns the PDF report.
What the API reports
Section titled “What the API reports”The intersection volume-to-capacity reported by the API is the highest lane-group volume-to-capacity.
On a signal, that value matches a Planning Guide intersection check when the greens are split in proportion to the critical lane groups. It diverges when a minimum green moves time from one street to the other. Send the facility cycle and lost time on the request. See Signal timing.