Traffic Control Decision Findings
The City has evaluated traffic patterns at the intersection of 51st Street and 154th Avenue and has determined that installation of a traffic signal is not preferable at this time. However, given community interest in a signal, the 51st Improvements project will install spare conduit where trenching is already occurring - a low-cost investment that reduces the cost of a signal if installed in the future.
Traffic Analysis Reports
This decision comes after two traffic analyses of the intersection at 51st Street and 154th Avenue/Place: the 51st Operational Analysis (PDF) and the 51st and 154th Supplemental Signal Warrant Analysis Assessment (PDF). The Operational Analysis concludes that a two-way left-turn lane on NE 51st Street would allow left-turns from the minor street approaches on 154th Avenue NE to make a two-step left-turn and use the two-way left-turn lane for refuge, therefore improving the level of service for the minor street [154th] left-turn movements.
A Supplemental Signal Warrant Analysis Assessment was also conducted to determine if a signal would be an appropriate traffic control device for this intersection at this time. The report evaluated Manual on Uniform Traffic Control Devices (MUTCD) signal warrants 1, 2, 3, and 7 and found that warrants 1, 2, and 7 are not met while warrant 3 is marginally met under one of the two conditions. Meeting one warrant means that it is allowable for a traffic signal to be installed but does not determine that it is required or even that installation of a signal is beneficial. The Supplemental Warrant Analysis concludes “because of the close access spacing and heavy peak hour volumes, the NE 51st Street corridor would likely be impacted by the addition of a traffic signal, particularly as it relates to vehicular delays and queuing.”
Federal Requirements & Guidance
A review of federal requirements and guidance found the following regarding traffic signal installation:
- Per the MUTCD “traffic control signals are often considered a panacea for all traffic problems at intersections. This belief has led to traffic control signals being installed at many locations where they are not needed, adversely affecting the safety and efficiency of vehicular, bicycle, and pedestrian traffic.”
- The Federal Highway Administration published a report titled Signalized Intersections: An Informational Guide in 2013 which states “practitioners should take care when using these warrants [warrants 2 and 3]. Many types of businesses generate these volumes at any given time. In most cases, this would not constitute justification for installing a signal” (Signalized Intersections: An Informational Guide, Federal Highway Administration, July 2013).
The MUTCD goes on to list alternatives to installing a traffic signal including “revising the geometrics at the intersection to channelize vehicular movements and reduce the time required for a vehicle to complete the movement.” As noted above the Operational Analysis found that the proposed two-way left-turn lane will revise the geometrics of the intersection and improve level of service.
The combination of the two engineering reports and review of federal requirements and guidance indicates that:
- The installation of two-way left-turn lanes will improve traffic operations at the intersection of 51st Street and 154th Avenue.
- Installation of a signal is allowed but should only be installed after careful consideration and after implementation of alternative treatments. In this case the installation of the two-way left-turn lane is the alternative treatment.
Following completion of the 51st Street widening project and the installation of a two-way left turn lane, the City will monitor the intersection of 51st and 154th to see if there is any significant increase in side street traffic volumes or collisions that may indicate the need to reconsider the warrants for a traffic signal at this location.