The design of a well-traveled portion of I-405 can cause major backups, and it is likely going to stay that way for some time.

Have you ever wondered why the HOV lane on southbound I-405 does not have direct access to the HOV lanes on I-90? The design there causes major weaving that ends up crushing the commute. Drivers have trouble getting from one side of the roadway to the other when they need to exit.

I went to Kim Henry, the person in charge of the entire I-405/State Route 167 corridor for the Washington State Department of Transportation, to find out why the HOV lanes in that spot don’t connect. There are some unique challenges based on existing structures and the geography, according to Henry.

Tell us what slows you down each day

For starters, there is a BNSF railroad bridge just west of I-405. Any ramp would have to go over the top of it.

“We need to give reasonable clearance over that,” Henry said. By the time the department could connect the ramp to I-90 the roadways would be well over the Mercer Slough.

The slough is environmentally sensitive. Because of the depth of the slough, the columns needed to support the ramps would have to be huge and cost-prohibitive to build, at least under the state’s current funding model.

“It just makes that particular project a very, very expensive project …,” Henry said.

So don’t expect any changes to your drive from the southbound I-405 HOV lanes to I-90 any time soon.

What will be changing on I-405 and SR 167 over the next 10 years is the expansion of the express toll lanes. The state is going to be adding a lane between Bellevue and Renton that will be incorporated into the toll lanes. So there will be two general purpose lanes and two toll lanes between Renton and Bellevue.

The state will also add direct access ramps between those toll lanes and the SR 167 HOT lanes in Renton.