Three weeks ago, I wrote about an anti-transit editorial that had the capacity loss on I-90 as one of its main arguments against ST2, because the link light rail will go through what is now the HOV section. The argument was that the loss of lanes from putting trains through the HOV section of the bridge would decrease overall car capacity.

However if you look at this graphic, ST2 will add one HOV lane in each direction on I-90 while removing the two HOV lanes in the center; thus there are no net lanes loss. And when you consider that almost half of the traffic across I-90 travels away from the city, you can see that the two HOV lanes travelling in just one direction is not as efficient as the two lanes in opposite directions. Basically 5 lanes in one direction versus 3 lanes in the other is only preferable if 65% or more of the traffic is going in one direction. However if almost as much traffic is going in each direction, it makes little sense to have more lanes in one direction. So with ST2, traffic and vehicle capacity on I-90 may be more than without it, and certainly people-moving capacity will increase. Isn’t that supposed to be the definition we care about now anyway?

5 Replies to “No Net Loss of Lanes on I-90 due to Light Rail”

  1. Nice find! I will shamelessly steal this nugget from you at some point. :-)

    Turning three lanes into four probably implies a reduction in the speed limit across the bridge, but that’s not too much of a loss.

  2. If you want the pdf I got that image from, I’d be happy to send it to you.
    You work at Microsoft, right? My name is Andrew Smith (Office).

  3. There IS a net loss in capacity. They can add the extra HOV lanes AND keep the center lanes. Putting light rail in the center decreases the capacity of the bridge – period.

    1. Jack,

      The completion of the R8A project (adding an HOV lane in each direction on I-90) is funded by the ST2 package.

      So no package: no HOV lane, but 2 express lanes.

      With package: 2 HOV lanes, no express lanes.

      So that’s no net loss in vehicular capacity; when you count the fact that the train can carry about 8 lanes’ worth of SOVs, there’s no comparison.

  4. Pingback: The Cross-Lake Battle That Already Ended - Seattle Transit Blog

Comments are closed.