Summary: the timing sheet is the signal’s DNA: phases, intervals, recalls, detector mapping, and TOD coordination plans. Reading one cold is a rite of passage; here’s the decode order.
Decode order
- Phase diagram: NEMA standard — odd = lefts, even = through (2/6 typically main street); ring-barrier shows concurrency (1+5, 2+6 | 3+7, 4+8).
- Per-phase intervals: min green · passage/extension · max1/max2 · yellow · all-red · walk · FDW (ped clearance).
- Recalls: min recall (always serves min green) · max recall (serves to max — effectively “pretend constant demand”) · ped recall · soft recall. Existing-conditions models must mirror these.
- Detection table: which loops/video zones call/extend which phase; delay/extend settings; failed detectors = phase behaves like recall (field notes matter!).
- Coordination block per TOD plan: cycle length · splits (must sum to cycle) · offset (start-of-green ref vs adjacent signals) · reference phase (usually coordinated 2+6) · permissive periods. Sheet times often in seconds AND percent — check units.
- Ped timing check: WALK ≥ 7 s typical (4 s min conditions)
#status/verify; FDW ≥ crossing distance ÷ 3.5 ft/s (MUTCD); confirm curb-to-curb distance used. - Clearance check: see Clearance Intervals and Ped Timing — recompute one approach; flag if sheet < computed.
Example application: before coding Existing in Synchro, transcribe the sheet into the model and note sheet date + plan # in assumptions. Cross-links: Synchro QAQC Checklist · NEMA Phasing and Ring-Barrier (the phase diagram decoded) · Offsets and Coordination (the coordination block decoded) · unclear fields → ask a senior, with the sheet in hand Free companions: STM2 (NCHRP 812, free PDF) — the chapter-by-chapter explanation of how every value on the sheet was developed. Practice question: splits for phases 2,4,6,8 read 42/28/42/28 on a 140 s cycle — what’s wrong? QA/QC reminder: never “optimize” existing conditions — model what the sheet says, cite sheet date.