---
title: "Signal"
url: "https://commonwaysystem.org/patterns/intersections/signal/"
id: "INT-SIG-03"
description: "Traffic signal control, available within the Commonway System only as a documented last resort, never the presumed choice."
updated: "2026-09-26"
---

# Signal

`INT-SIG-03`

Situational / Discouraged Intersections & Crossings

Signal

A signalized intersection, controlling conflicting movements with timed lights.

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.[1][2] 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.[3][4] This applies to every signal installation, not just those on freight-priority streets. [Industrial Collector](https://commonwaysystem.org/patterns/collectors/industrial-collector.md) 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](https://commonwaysystem.org/patterns/elements/curb-extension.md).

## Related patterns

[Roundabout (Single/Multi-Lane)](https://commonwaysystem.org/patterns/intersections/roundabout.md) (INT-RAB-01) and [Turbo-Roundabout](https://commonwaysystem.org/patterns/intersections/turbo-roundabout.md) (INT-TRB-02) (explicitly named on this page as competing for the same higher-volume intersections); [Median U-Turn](https://commonwaysystem.org/patterns/intersections/median-u-turn.md) (INT-MUT-12), [Restricted Crossing U-Turn](https://commonwaysystem.org/patterns/intersections/restricted-crossing-u-turn.md) (INT-RCU-13), and [Displaced Left-Turn](https://commonwaysystem.org/patterns/intersections/displaced-left-turn.md) (INT-DLT-14) (unconventional geometries that modify rather than replace this pattern to remove unprotected left turns)

## References

1.  Legal / regulatory [Washington State Department of Transportation, _WSDOT Design Manual_, Chapter 1300, "Intersection Control Evaluation."](https://wsdot.wa.gov/publications/manuals/fulltext/m22-01/1300.pdf)
2.  Legal / regulatory [Manual on Uniform Traffic Control Devices, 11th Edition with Revision 1 (FHWA, December 2025; effective March 5, 2026), Chapter 4C.](https://mutcd.fhwa.dot.gov/pdfs/11th_Editionr1/mutcd11theditionr1hl.pdf)
3.  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).](https://www.gao.gov/products/gao-26-107954)
4.  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).](https://doi.org/10.3390/su14169805)
5.  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).](https://www.iihs.org/news/detail/vehicles-with-big-blind-zones-spell-danger-to-pedestrians-during-left-turns)