Freeway ramp meters reduce collisions and decrease travel times

Jeff Thorngren of Snohomish writes: The state Department of Transportation needs to time the daily opening of the U.S. 2 trestle eastbound shoulder lane with the on-ramp meter lights from 41st Street onto northbound I-5. Traffic regulating lights on the 41st on-ramp start around 2 p.m. The open-shoulder driving on the eastbound trestle should open to traffic at 2 p.m. instead of 3 p.m. as it does now.

Dave Chesson, a spokesman for the transportation department, responds: Depending on traffic conditions, the ramp meter lights on the 41st Street on-ramp to northbound I-5 are typically turned on between 2 and 3 p.m.

The ramp meter at 41st allows only one vehicle per lane during each green light, creating a 4-to-15 second delay between cars entering the highway. This delay helps reduce disruptions to I-5 traffic and reduces collisions that can occur when vehicles merge onto the highway.

Ramp meters are used to reduce collisions and decrease travel times for drivers. Without ramp meters, multiple cars try to merge simultaneously and drivers on the freeway slow down to allow them to enter, and these slower speeds quickly cause backups. If cars enter the highway in controlled intervals, they are less likely to cause a disruption to the traffic on the freeway. A short wait on the ramp increases average freeway speeds and shortens overall freeway travel times. Ramp meters can also reduce the number of collisions that often occur when multiple vehicles merge onto the highway at the same time.

As the writer mentions, traffic can use the eastbound trestle shoulder between 3 and 7 p.m. weekdays. We selected these hours based on analysis of traffic volumes, so that we provide the most benefit for travelers. We need to balance good traffic flow against having the shoulder available for vehicles to use in case of breakdowns or emergencies. Traffic volumes begin increasing at 2 p.m. and are at their peak between 3 and 6 p.m., before they start dropping off. During off-peak periods, volumes are lower and speeds are higher, so the shoulder lane would have little additional benefit if it was available. At this time we don't have any plans to change or expand the hours of operation.

More information about ramp metering is available at www.wsdot.wa.gov/Traffic/Congestion/rampmeters/ and www.wsdot.wa.gov/Projects/US2/TrafficManagement/default.htm

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