Horeshoe Curve on NY 17 in Wurtsboro, NY

[roadman65]

Why is the Quickway built like this around the US 209 junction?  The highway is perfectly aligned until you hit Wurtsboro, NY and then it turns to the SW only to loop around, interchange with US 209, and head back to its original heading.  I know the toparary is mountainious with a valley where US 209 is, but what about rock cutting through mountains?  I know that Wurtsboro is not upscale enough to alter a major freeway either. 

Also, at one time there was an at grade railroad crossing on the freeway near there, that not only is unusual for a freeway, but also controlled be a traffic signal and not the standard flashing red signals on the crossbuck as stated in the MUTCD.  I do not know if it is still there, but it has to come out and be grade separated if I-86 is to arrive there.

[Alps]

Topography is the answer. Look at the terrain west of town. There are two ways out of the mountains, one that is the old road straight through the middle of town, and the other that NY 17 follows. Anything else would require blasting away a lot of mountainside or a tunnel.

[Buummu]

I like the horseshoe curve on NY 17-future I-86..

[yakra]

The way the road climbs diagonally up the mountain rather than straight up the side, you get the same rise over a lot more run. compare how long NY17 takes to descend from the 800' contour interval to the valley floor, vs, say, something that'd parallel Sullivan St a little bit south. You get much more sane grades.

[mightyace]

^^^

Or not having to build a high, expensive bridge, etc.

For Interstate standards, there is a maximum grade normally allowed. I think it may be 3 or 4% but, I wouldn't be surprised if I'm wrong.

And, yes, this road was not built as an interstate, but generally, modern road building tries to keep grades "sane".

There are, of course, exceptions.  (See I-24, Monteagle, TN)

[Alps]

I want to say grades are 5% max, 6% for short distances or where necessary. Don't have the right book in front of me.

[InterstateNG]

Paragon of accuracy Wikipedia notes 6% is the maximum allowed.

[Sykotyk]

I believe 6% is the max allowed by default, but I think there's somewhere in the country with a 7% (maybe I-64 in southeast WV?). As with any mountain interstate, there can be deviations in the standards for special circumstances.

[agentsteel53]

why am I randomly remembering the Grapevine northbound, final descent into the Central Valley, as being 6.5%?

I've driven it so many times that the signs have lost all meaning to me, so I may be conflating the 65 mph speed limit and 6% grade.

[roadman65]

I like the horseshoe curve on NY 17-future I-86..

Oh its nice, do not get me wrong!  I was just curious.