February 2nd, 2011

UDOT GETS FLASHY

Optimize Mobility, by Catherine Higgins.

Have you noticed? UDOT is installing  safer, driver friendly, and energy saving flashing yellow arrow left-turn signals in many intersections.

Flashing yellow arrows are easier to understand for most drivers.

A seven year study done by TRB‘s National Cooperative Highway Research Program shows that flashing yellow arrow left turn signals (FYA) offer operational flexibility for traffic engineers. And because FYA are more easily understood, drivers make fewer mistakes.

Improved flexibility equals more turn time: FYA allows traffic engineers to change the order of the signal phases to allow green time to be staggered to accommodate vehicles arriving at intersections.

Flexibility allows “more options to handle variable traffic volumes, including the ability to change by time-of-day between protected only, protected/permissive only and permissive only indications,” according to Mark Taylor, Signal Systems Engineer at UDOT’s Traffic Operations Center.

Flashing yellow arrow signals were recently installed at 9620 South State Street in Sandy, Utah.

Improved safety: The FYA was shown to be more intuitively understood, resulting in  fewer crashes during heavy traffic.

The traditional signal box houses five signals, three of which are indications for both through traffic and left turns. ”The FYA separates the signals out from the through vehicles and left turn vehicles to keep it more simple,” explains Taylor.

For road users, FYA use results in reduced delay, fewer crashes, less pollution from vehicle emissions and decreased fuel consumption.

It’s official: A new updated UDOT policy incorporates flashing yellow arrows and establishes warrant criteria required for signalized intersections.

UDOT will switch to FYA where funds allow.  For new construction, FYI will be installed where warranted, according to the new policy.

In existing intersections, FYA left turn signals will be installed depending on conditions. For example, the mast arm must be long enough to accommodated the signal head. Replacing a mast arm and possibly installing a new support column can be prohibitively expensive.

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