Like water poured too quickly through a funnel, when traffic backs up on Interstate 5 it overflows and makes a mess of Vancouver’s west side and downtown.
While those diverting drivers may save themselves time, transportation officials say they’re making things worse on streets and on the highway.
“It is a big problem because the local streets are acting as a regional bypass,” said Patrick Sweeney, Vancouver’s principal transportation planner. “You have a local street network that’s designed for local traffic, however it’s handling this pulse traffic that uses it as bypass.”
As congestion on southbound I-5 during the peak travel times between 6 a.m. and 8 a.m. has grown, so too has the traffic in Vancouver’s west-side roads. That was the case Monday morning after a crash in the middle of the bridge span.
Washington State Department of Transportation said when people use Vancouver’s streets to get ahead of some I-5 congestion they’re actually making the entire traffic jam behind them worse.
“By doing the queue jump they cause so much turbulence that the amount of vehicles we can get through the (I-5) corridor drops,” said WSDOT Traffic Engineer Scott Langer.
Essentially, people are driving straight to a choke point, and other drivers that slow down and make room for them are reducing the road’s capacity. WSDOT estimates that each time a vehicle jumps the queue to enter the highway it hampers the progress of two other drivers in the mainline.
“You may be saving yourself some small amount of time, but you’re impacting everyone else,” Langer said.
The city’s Westside Mobility Strategy reports southbound morning travel times on I-5 went up 291 percent from 2011 to 2015, and speeds dropped from 31 mph to 8 mph, respectively. The report estimates that between 1,300 and 2,800 vehicles per week use Main Street to get onto I-5 in downtown in the morning rather than staying on or even getting on I-5 farther north.
The per-mile collision rate on Main Street is more than double the average of a comparable street, and many of those crashes happen around the street’s intersection with other arterials that connect to I-5, the report said.
“Both improvements to Main Street and to I-5 are necessary to restore safe and efficient traffic flow on one of Vancouver’s most important streets,” the report reads.
When traffic backs up at the I-5 on-ramp downtown, C-Tran’s buses can’t make stops at Turtle Place. Since The Vine started in January, C-Tran has had to close the Turtle Place stop at least 26 times because of traffic. Those closures can cause passengers to miss their bus. Traffic jams can cause buses to fall behind schedule, which can disrupt service for hours.
“We knew it would be an occasional issue,” said Scott Patterson, C-Tran’s director of planning, development and public affairs. “We didn’t expect it to be as big of an issue as it’s become.”
Less obvious than traffic congestion, but still significant, the Westside Mobility Strategy states, are the impacts of high volumes of traffic entering the west-side neighborhoods via the I-5 78th Street Exit 4 and driving Fruit Valley Road; longer freight travel times between I-5 and the Port of Vancouver and freight traffic for longer periods throughout the day; the high collision rates on some west-side streets; the daily weekday traffic backups on 6th Street, Washington Street, and Columbia Street leading up to the Washington Street I-5 southbound on-ramp — among others.
Short of a massive capital project on I-5, transportation officials say solutions are limited.
The city is looking to balance mobility needs with neighborhood liveability, that includes steps like extending Northwest 32nd Avenue west of Fruit Valley Road and last year’s step to ban freight traffic from 39th Street.
One possible step that hasn’t risen to the top of the list is implementing a road diet on upper Main Street, which would reduce the number of lanes from four to three, one of which would be a turning lane. It’s a technique that’s proven to reduce crashes and improve pedestrian crossings.
Patterson said no official proposals are in place, but the agency has talked with the city about limiting the far left lane on Washington Street until Turtle Place to buses, or turning parking spaces on a couple of blocks into a transit-only lane for a few hours in the morning.
WSDOT also is considering metering the on-ramps throughout downtown Vancouver.
Placing traffic lights at the on-ramps could not only ease the flow onto I-5, which keeps traffic moving, but it would take the advantage out of driving through downtown by forcing people to wait at a light.
A metering study is underway. But even if it proves to be a solution, funding could be challenging to obtain and years away, Langer said.
“There’s not a lot of funding options for these lower-cost solutions,” he said.