Drivers will notice active ramp meters on the Mercer Street ramps to I-5 this weekend as part of a one-month testing phase.
The meters — on both the north and southbound ramps — will only be active on the weekends for the first month as the Washington State Department of Transportation works out the kinks. They’ll go active during the week in early April.
State traffic engineer Morgan Balogh believes the impact on I-5 will be instant.
“We should see the number of crashes go down about a third and we should see the volume through the area go up maybe three to five percent,” Balogh said.
That number would likely be higher if I-5 drivers would allow people to merge a little easier, but we can talk about the Zipper Merge later.
The biggest question I have received about this plan is what this will do to Mercer, which we all know is already terrible. Balogh and the Seattle Department of Transportation have said it won’t have much of an impact on Mercer because it’s already so bad.
“It backs up now,” Balogh said. “We’re going to let the same number of vehicles go through in the future as we do now, so there shouldn’t be any difference or any additional impacts.”
In the northbound direction, the new ramp meters will only be active during the morning commute, before the express lanes open in that direction. That will allow two lanes to queue up. In the southbound direction, WSDOT is adding a little queuing capacity.
“We have two lanes now, so we’re going to take the shoulder and add a third lane that will be operating when the meter is running,” Balogh said. “We’ll have more storage, and we’ll be able to have more flexibility in how we release the traffic.”
You might be wondering why it took the state so long to meter one of the busiest ramps in the region and the answer is simple. WSDOT wanted to wait for Seattle to make the improvements to Mercer before implementing the meters.