Signal
INT-SIG-03 Signal
Typical at: Compact Urban Core
Suburban is an edge case. Undeveloped and Rural are unlikely pairings.
Note
Signal remains available within the Commonway System, but only as a last resort requiring documented burden-of-proof justification, modeled on WSDOT's Roundabout First and Intersection Control Evaluation policy.12 It is not banned, just never presumed. Where a roundabout or turbo-roundabout can serve the same volume, that is the default choice instead.
Design notes
Signal's realistic density range overlaps heavily with Roundabout and Turbo-Roundabout, since all three ultimately compete for the same higher-volume intersections. The difference is which one the Commonway System treats as the presumed choice absent a documented reason otherwise.
Turning-maneuver risk to people walking and biking
Vehicles making a turn are involved in a disproportionate share of fatal pedestrian and cyclist crashes relative to vehicles going straight, and that risk rises sharply with vehicle size.34 This applies to every signal installation, not just those on freight-priority streets. Industrial Collector is the acute case of it.
- Leading pedestrian intervals. Give pedestrians a several-second head start into the crosswalk before the parallel vehicle phase turns green, so a turning driver has a chance to see the pedestrian before beginning the turn.5
- Curb extensions. They shorten crossing exposure time and place waiting pedestrians directly in the turning driver's line of sight.5 See Curb Extension.
Related patterns
Roundabout (Single/Multi-Lane) (INT-RAB-01) and Turbo-Roundabout (INT-TRB-02) (explicitly named on this page as competing for the same higher-volume intersections); Median U-Turn (INT-MUT-12), Restricted Crossing U-Turn (INT-RCU-13), and Displaced Left-Turn (INT-DLT-14) (unconventional geometries that modify rather than replace this pattern to remove unprotected left turns)
References
- Legal / regulatory Washington State Department of Transportation, WSDOT Design Manual, Chapter 1300, "Intersection Control Evaluation."
- Legal / regulatory Manual on Uniform Traffic Control Devices, 11th Edition with Revision 1 (FHWA, December 2025; effective March 5, 2026), Chapter 4C.
- Evidence-based U.S. Government Accountability Office, Pedestrian and Cyclist Safety: DOT Should Take Steps to Address Risks Related to Limited Driver Visibility, GAO-26-107954 (2026).
- Evidence-based Wang, Q. et al., "Exploring the Influencing Factors and Formation of the Blind Zone of a Semitrailer Truck in a Right-Turn Collision," Sustainability 14(16), 9805 (2022).
- Evidence-based Insurance Institute for Highway Safety, "Vehicles with big blind zones spell danger to pedestrians during left turns" (November 19, 2025) (leading pedestrian intervals and curb extensions as blind-zone mitigations).