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Castle Rock adding flashing yellow arrows at intersections

T-bone crashes lead to changes in 19 additional locations around town


If residents have noticed flashing yellow arrows on Castle Rock traffic signals, they'll soon see many more throughout the community.

The arrows already exist at several intersections but the town announced in November it will be installing them at 19 more intersections, with work lasting through January. Residents will find crews along Front Street, Fifth Street, Meadows Boulevard, Plum Creek Parkway, Wilcox Street and Wolfensberger Road until the project is complete.

Transportation Planning and Traffic Engineering Manager Ryan Germeroth answered questions on the flashing yellow arrow project.

What are the flashing yellow arrows seen on Castle Rock's traffic lights?

The flashing yellow arrow is displayed above a green turn-arrow. The intended message conveyed by the flashing yellow arrow is that the left-turning motorist needs to yield to traffic in the opposing direction before making a left turn in an available gap in traffic.   

Can you give us a brief history of these traffic signals in Castle Rock? When were they first implemented in town, where and why? 

The flashing yellow arrow was first implemented in Castle Rock in 2011 as part of the signal construction project at the intersection of Meadows Parkway and Limelight. With that construction, Castle Rock was one of the first agencies in the State of Colorado to implement a flashing yellow arrow operation. At the time, it was implemented due to the safety and operational benefits documented with flashing yellow arrow. It was intended to be a pilot intersection for how the operation could be expanded further in Castle Rock.

Since that construction in 2011, flashing yellow arrow has been a standard installation with any new traffic signal construction or traffic signal modification project in the town. A total of 18 intersections have either been constructed with or retrofitted with flashing yellow arrows since the completion of the Limelight project in 2011. This total includes three intersections on Founders Parkway, which is owned and maintained by the Colorado Department of Transportation.

How effective are these arrows?

National data has shown a 20 percent reduction in the occurrence of crashes involving left-turning vehicles at intersections with flashing yellow arrow. The town has experienced similar reductions in crashes in existing intersections that have been converted to flashing yellow arrow operation. The conversion at the intersection of Founders Parkway and Front Street is the most relevant example to date. The intersection used to have a crash pattern of northbound left-turners colliding with southbound through traffic. Since the implementation of flashing yellow arrows, the crash pattern has subsided. In addition, flashing yellow arrow provides the town's traffic engineers more flexibility in the operation of the left-turn phases in town as traffic volumes change in town through the day, which in turn improves safety and reduces delay for the traveling public.

The town will be installing the arrows at 19 new intersections. Why is Castle Rock expanding the program and how were these 19 locations selected? 

Flashing yellow arrow is now a town standard for traffic signal construction and operations. The goal with the current project is to make the operation standard across the town, which should help to improve left turn safety and operations town-wide. There will also be benefits from a driver expectancy and understanding as every intersection will be equipped with flashing yellow arrows. The 19 intersections included in this project are the existing town intersections that currently do not have a flashing yellow arrow operation. The determination of whether a green arrow will be included with the installations in the project is based on an assessment of traffic volumes at the intersection. 

What will the public need to know as crews begin work installing the lights? 

Typically, work will occur during the day between 8 a.m. and 3:30 p.m., Monday through Friday. The work should move relatively quickly with some lane closures needed to replace the overhead signal heads and corner closures to replace the signal heads mounted to the poles on the corners. Generally, each intersection will take about two days to convert. During that time, the left turn phase operation may be more restrictive with green and red arrows only until we are able to convert the full intersection.


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