I -278 in New York City

You must be talking about Atlantic Ave off the BQE.. I never exit there - was always told to stay in the left lanes and have never had a problem..

 

On 278 you have to get off on Astoria Blvd once you go over the Triborough bridge going west and before it going east at I believe exit 44. I have screwed up before and didn't get off and made it under the bridge, but I believe you can get an expensive ticket if you do not get off.
When you get off you run Astoria Blvd to the ramp to get back on about a mile.

 

Probably; NYC measures from the center of the wheel (hub) to the bottom of the bridge, not from the ground to the bottom of the bridge.

In my opinion they should take those signs down because they cause a lot of confusion=more congestion.

 

I had the distinct pleasure of running an account for Swift back in 2004 that took me from Newburgh, NY (about a 40 minute drive from my house at the time), on two trips to NYC each night. The first would always put me in Teterboro, NJ or somewhere in Queens. The second I somehow always got stuck with the Syosset, Long Island run with a 4:30am departure time from the Newburgh terminal. It made for some slow moving traffic coming back the L.I.E. and the Cross Bronx expressway at 7am. Thank goodness for Howard Stern. On more than a few occasions in NYC I've come across signs that mark bridges well less than 13' 6", and every time, upon either calling dispatch, or getting on the CB, I was assured that it's fine, go on under.

I took a wrong exit once and ended up on Queens Blvd. I had to make a turn around on a side street exit, which was elevated with an elevated train track on the re-entry side. Marked 12' 8"... I had traffic blocked for 5 minutes while I G.O.A.S (got out and stared). Once again, I hop on the radio and say "Hey, it was suggested I turn around here, but the sign says I can't clear this." Numerous comebacks assuring me it's fine and I can make it under. Interestingly enough, I made it with a few inches clearance.

Fun times.

Conversely, there's a bridge on RT 209 just after crossing from PA into NY. I don't know any technical name, but it's one of those bridges that's at "street level" and the road dips under it. You know what I mean, I hope. At this time I was still riding with my "student partner", Swifts bonehead policy which I will never, ever do again. I came upon this bridge and saw the clearance warning, so I woke him up from the sleeper and asked him to help me turn around. We're getting set to do it, when an obviously bored restaurateur came outside and insisted we can make it under, that "Truckers do it all the time."

I took another look at the bridge, and the curve in the road and said "No way we're clearing that." The restaurant owner was genuinely offended! My partner said, "Just drive under it man..."

This guy was 15 years older than me, and an ex army guy. He knew EVERYTHING, or at least, way more than I did (in his eyes). We bucked heads multiple times. After trying to get him to understand that, yes, we'd make it half way under before the tractor lifted the trailer into the bottom of the bridge on the other side, I said "Ok... I'll log off duty, you log onto driving, and you take it under."

He agreed, and to make a long story short (probably too late), I ended up helping him turn the truck around in the middle of an intersection. The restaurateur had long since abandoned his hopes of seeing an accident.

 

I run the city all the time, I have made it under a bridge on 116th st in Manhatten that was marked 12'0". The key with NYC is you need to follow the 5 boro truck route map. If it is a designated truck route I believe you can make it under the bridges. In my travels I have found this to be true. Brooklyn Linden Blvd marked 12'4 no problem, Kings Highway marked 12'2 no problem, Utica Ave 12"2 no problem, You get the Idea. I would just say use common sense, go under these bridges slow and if you are not sure, creep under and watch your mirror, if you go slow enough and hear a scrape back up and turn around. But I do believe the NYC truck route map is the key.

 

And here is the link where you can get said map for free and other NYC truck info:

http://www.nyc.gov/html/dot/html/motorist/trucks.shtml