Manhattan Bridge - why'd they rebuild it wrong?

[Deucey]

(I'm stuck on a  on the bridge right now, and this popped up in my head.)

I think it's a given that if anyone understands the basic concepts of structural engineering, having trains operate along the outside edge of a bridge is a bad idea - since the weight of a train causes one side to lift (and the other to dip) as the train crosses.

Factor in the Manhattan Bridge, and you have this torsional seesaw effect.

From what I remember from being a teenager visiting here in the 90s, it was that torsional seesaw effect that led to the bridge having one set of tracks closed while structural repairs were made.

But given that even with the repairs made, at some point, they'll be needed again, coupled with the crapshoot that is DeKalb Junction, why didn't DOT and  redo the bridge and tunnel leads so the roadways are on the outside (like with Queensboro Bridge) and the tracks - even if it's a two-track line - are on the inside?

 

[Enjineer]

4 minutes ago, Deucey said:

But given that even with the repairs made, at some point, they'll be needed again, coupled with the crapshoot that is DeKalb Junction, why didn't DOT and  redo the bridge and tunnel leads so the roadways are on the outside (like with Queensboro Bridge) and the tracks - even if it's a two-track line - are on the inside?

It'd have required a much larger rebuilding project, necessitating reconstruction of the tunnel portals on both sides, as well as the roadway on and off-ramps. They added "torsion tubes," IIRC, which help absorb some of the forces the bridge experiences when trains cross it, reducing the wear and tear from pre-reconstruction levels.