Time-of-Day Plans

A signal doesn’t run one timing — it runs a schedule of plans. Each time-of-day (TOD) plan is a complete package: cycle length, splits, offset, sometimes phasing sequence (lead/lag flips), each built for a different traffic condition. STM2 (NCHRP 812) Chapters 5 and 7 cover plan development and scheduling.

Typical weekday structure

Quote

“The simplest schedules typically define an a.m., off-peak, and p.m. peak for weekdays and a different set of plans for weekends.” — FHWA Signal Timing Manual (FHWA-HOP-08-024), Ch. 6

A common Florida arterial weekday looks like:

 Plan       When (typical)      Character
 ─────      ──────────────      ─────────
 AM peak    ~06:30–09:00        Long cycle, splits/offsets favor peak direction
 Midday     ~09:00–15:30        Moderate cycle, balanced splits
 PM peak    ~15:30–19:00        Longest cycle, offsets favor opposite direction
 Off-peak   evening             Short cycle or coordination dropped
 Free       late night          Uncoordinated, fully actuated — first come, first served

Weekends usually get their own plans; agencies may also program holiday, school-day, event, or hurricane-evacuation plans. “Free” isn’t a plan so much as the absence of coordination — the controller just answers detector calls.

How the plan gets picked

• Time-of-day clock (the default): the controller (or central system) activates plans by day-of-week and time from a stored schedule, all synced to a master clock. Cheap, predictable — and blind: it runs the PM-peak plan on a rainy game day and on a quiet holiday alike.
• Traffic responsive: the system picks among the stored plans based on what system detectors currently measure. Better fit to unusual days, but it needs healthy detection and tuning — many agencies own the feature and still run the clock.
• Manual/operator override: events, incidents, evacuation.

Every plan change triggers a transition period of degraded operation — see Offsets and Coordination for why schedule boundaries shouldn’t be stacked close together.

Before you retime: what to collect

• Turning-movement counts for each plan period you’ll rebuild — not just the AM/PM peak hours. A midday plan built from PM counts is fiction.
• The current timing sheets and the TOD schedule itself (plan numbers, start times, day plans) from the maintaining agency — the schedule page is part of the timing sheet package; ask for it explicitly.
• Existing cycle/splits/offsets per plan as your baseline, plus any coordination diagrams.
• Detector status/maintenance notes — a failed detector puts a phase on recall and quietly reshapes how the “same” plan actually serves traffic.
• Field observation during each period — queues, split failures, where platoons actually arrive. If the agency has ATSPM, pull it instead of guessing (see Signal Timing Manual (STM2) and Free Training).

The review question

“Does the model period match the plan actually running?” Ask it on every existing-conditions review:

• Counts collected 4–6 PM must be modeled against the PM plan, not whatever plan happens to be first on the sheet.
• Check the boundaries: a 4:00–5:00 count at a signal whose PM plan starts at 4:30 straddles two plans (plus a transition) — pick the period or footnote the mismatch.
• Saturday analysis with weekday plans, or a school-zone study during summer TOD settings, is the same error in different clothes.

Warning

The timing sheet in the project file shows all the plans; it doesn’t tell you which one was live during your count. Match count timestamps to the TOD schedule, and confirm the sheet’s date — plans get retimed, and an old sheet plus new counts is a silent mismatch. Note plan number and sheet date in the model assumptions, per How to Read a Signal Timing Sheet.

Example

Synchro existing-conditions review: model says 120 s cycle, counts stamped 12:00–13:00, TOD schedule shows the midday plan is 100 s and 120 s doesn’t start until 15:30. Comment: “Existing midday model uses PM-plan timing; recode to Plan 2 (100 s) per TOD schedule dated on the sheet.”

Tip

STM2 is a free PDF from National Academies Press (link above) — Chapter 5 for how many plans a day actually needs and Chapter 8 for implementation. FDOT’s free Signal 101/102 CBTs cover Florida conventions for the same material.

See also: Offsets and Coordination · How to Read a Signal Timing Sheet · Synchro QAQC Checklist