Why did the Washington Department of Transportation take away one lane on southbound Interstate 205 at the mall exit?
That was just one of many road-related questions readers suggested for a Clark Asks story. Even if you didn’t reach out to us, odds are good you’ve asked yourself that same question if your commute on I-205 starts somewhere north of the state Highway 500 interchange.
The short answer: congestion.
“More lanes does not always equal better flow,” said Scott Langer, a traffic engineer with the Washington State Department of Transportation. “What’s important is how the lanes flow into the system.”
Traffic from both eastbound and westbound state Highway 500 merge onto southbound I-205 at two different spots — just before the freeway and the other directly at the mainline. Before WSDOT changed the merge configuration this summer, this area of I-205 had three lanes, which was fine for those already on the freeway but caused a lot of slowing and congestion at those two merges between those already on the interstate and those trying to join them — especially during the morning rush hour. Those conflicts caused a chain reaction up onto state Highway 500, leaving commuters stuck in long back ups and in thick congestion well before reaching the southbound I-205 offramp.
“Before the change, the traffic would backup onto 500, and that would cause crash problems,” Langer said. “That problem is now gone.”
In mid August, WSDOT restriped portions of southbound I-205. Workers restriped the freeway north of the interchange, reducing it from three lanes to two and giving Highway 500 its own lane for a longer, and thus smoother merge into I-205 traffic.
WSDOT didn’t do a large formal study before making the changes. They based the decision off of observations of a perennial problem at the interchange. And because its much cheaper and faster to lay down paint than it is to rebuild portions of the highway, they decided to adjust the road and see if it worked.
“The theory here is its really not that expensive of an improvement. If worse came to worse, we’d take the marking back out,” Langer said. “The risk-versus-reward, the amount of money it costs, we though, ‘Lets try it out and see what happens.’ From what we see, it’s taken care of that merge point.”
Langer acknowledges that although the changes have things easier on some commuters, it’s likely made it less convenient for others.
In the mornings, when southbound traffic backs up to Padden Parkway, drivers used to be able to use the old lane, which had little traffic in it, and zip around all the other congestion and either cut back into the other lanes, or just cruise right down to the Mill Plain exit. Well, those days are no longer.
“We had to balance allowing people to do that with the problem it caused at (Highway) 500,” he said. “Those few people were outweighed by the people suffering on 500.”