>>1405395Most, but not all, the elevateds in NYC have columns on the sidewalks instead of the street, reducing the chances of collisions. I believe the old lines are so overbuilt that collisions don't create a risk for the structure, not at the speeds people drive on the streets below (usually narrow, one lane roads). They're built high enough that there's no height restrictions unless you were, I don't know, towing in some mega-oversize structural element that needs 30 feet of clearance. Bridge strikes, as you alluded to, can be very serious and damaging. The speed limit here in the city is 25 mph so generally if a strike was to happen it'd not be as bad as say a 50 mph truck on a 3 lane highway (now that's an issue for the Belt Parkway).
Your point about actually constructing a line, now yes absolutely that's a major issue in a lot of cities. For NYC, for example. the NYCDOT and the Mayor's office are so weak that god knows they'd NEVER even consider closing a street 24/7 for construction. That being said, if the political will was there, outright closing it would be a no brainer. Like I said, many lines here are over narrow one lane roads (one lane each direction). It's not going to be the end of the world if you close these kinds of streets, especially if you do it in sections.
