Safety-Driven Traffic Signal Modifications

Traffic signal phasing modifications are a tool identified within Arlington’s Vision Zero Multimodal Safety Engineering Toolbox used to improve safety by reducing conflicts at intersections. Signal phasing modifications provide safety benefits in time - changing the way that the signal system gives time to different intersection users at different moments in the traffic signal cycle. These improvements are not always easy to see but make major improvements to safety.

What are traffic signal phasing modifications? 

There are different types of phasing modifications that can be made to improve safety depending on the mix of different users, intersection design, and severity of potential conflicts, for example:

• Protected Left-Turn Phasing provides a dedicated left turn phase by separating the turning movement from any other conflicting traffic or pedestrian movement. A protected left turn is controlled with a left turn arrow on the signal display.
• Changes to Phase Sequencing involves changing the order in which movements are served. Rearranging phases can help reduce long queues and can also align sequences to promote longer pedestrian WALK intervals. This tool requires an extremely specific set of circumstances to provide benefits.
• Split Phasing separates traditionally concurrent phases by approach. In other words, one side of the street is serviced separately at a different time. This type of phasing helps remove left turn conflicts from pedestrian crossing phases but will likely result in increased cycle lengths and queuing and will significantly increase pedestrian delays crossing the mainline street.
• Other safety updates such as pedestrian accessibility modifications, turn prohibitions, and other ITS signs or indicators to control traffic at the intersection.

Adjustments in signal phasing can be relatively low cost, requiring engineering design and modification of signal equipment. However, on large-scale projects or projects involving older equipment, it could require longer timelines and cost commitments. Additionally, adding exclusive turn phasing may necessitate new signal equipment configurations, which increases the cost significantly.

Learn more about traffic signal phasing modifications by viewing the toolbox cut sheet. 

Recent & Upcoming Modifications 

Arlington has been adjusting and improving traffic signal phasing modifications for decades. Recognizing our Vision goals of putting safety first and providing accountability and transparency, we started publishing a list of all traffic signal phasing modifications in 2025. See below for what has recently been installed or if coming soon.

2026

2025