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?