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Traffic Q&A: Ramp meters should help speed I-5 traffic near JBLM

Question: I think I saw ramp meters working at Joint Base Lewis-McChord yesterday. Great! It definitely helped. How about more information on it? Thanks.

— Ken Rose, Tacoma

Answer: Yes, you saw right. On May 18, the state Department of Transportation turned on ramp meters at 11 freeway intersections near JBLM, where traffic routinely slows to a crawl during the morning and afternoon commutes.

Ramp meters — on/off traffic signals that control the rate at which vehicles enter the freeway – now can control access to northbound and southbound Interstate 5 for a distance of 15 miles — from Marvin Road in Lacey to state Route 512 in Tacoma.

Transportation Department spokeswoman Claudia Bingham Baker said the meters are part of a federally funded project to install “smart highway devices” along the notoriously congested JBLM corridor.

The large, computer-operated system is managed in the agency’s Traffic Management Centers.

Traffic detection devices, including magnetic loops and radar, detect speeds and volumes on freeway lanes and ramps. The data are fed to the ramp meters, which automatically alter their cycles to maximize traffic flow.

Here’s the department’s rationale for ramp meters: without them, multiple vehicles try to merge simultaneously. Drivers on the freeway slow to let them in, which causes backups.

If vehicles enter the freeway in controlled intervals, traffic engineers say, they’re less likely to disrupt the freeway flow.

Bingham Baker says ramp meters also reduce accidents. Some studies have shown they cut collisions by as much as 30 percent.

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