Yellow (ITE kinematic)
y = t + v/(2a + 64.4g)
Legend: t = perception-reaction time (typically 1.0 s); v = approach speed in ft/s; a = deceleration (typically 10 ft/s²); g = grade as a decimal (downgrade negative).
Practical FL range ~3.0–6.0 s by speed; many agencies use posted-speed lookup tables — the AGENCY TABLE governs #status/verify.
All-red
AR = (W + L) / v — intersection width + vehicle length (≈20 ft) over speed; commonly 1–3 s.
Ped
WALK (≥7 s typ.) + FDW = D/3.5 fps; verify agency use of 3.0 fps total-crossing check and where D is measured (curb-to-curb vs to far side) #status/verify.
Worked example
45 mph (66 ft/s), flat: y ≈ 1.0 + 66/20 = 4.3 s. W=90 ft: AR ≈ (90+20)/66 ≈ 1.7 s.
Common mistake
Using design speed instead of the speed the agency’s policy specifies (posted vs 85th) — ask which.
QA/QC
Recomputed vs sheet; discrepancies flagged to PE, never silently “fixed.”
Free companions: FHWA Signalized Intersections Guide (FHWA-SA-13-027) and STM2 — free PDFs covering clearance and ped-timing practice behind these formulas.
See also: How to Read a Signal Timing Sheet · NEMA Phasing and Ring-Barrier (which phase each Y/AR belongs to) · Offsets and Coordination (clearance times live inside every split)