How do truckers learn ahead of time how to avoid bridges lower than their load?

Question

Is there a map somewhere, where they can map out a route?

Is there a minimum bridge clearance height (not likely) or a maximum height to semi-tractor trailer loads?

I've seen big rigs stuck under bridges bec of no clearance, but its very rare. It seems it wouldn't be that rare.

How do the truckers know ahead of time which low bridges to avoid?

Answer 1

It's in the rand mcnalley motor carrier atlas. Lists bridge clearence and restricted routes that trucks cannot go on or under. Sometimes when u see a truck stuck under a bridge, the clearence was ok until the state repaved under the bridge and forgot to change the sign.  More pavement = less clearence

Answer 2

they don't. the bridge on my street is hit every day despite the signs

Answer 3

Most of the low bridges on the designated truck routes, are listed in the Motor Carrier's Atlas.  Generally speaking, if a state has designated a road as a 'truck route' (these roads are highlighted in orange in the Motor Carrier's atlas)....the bridges are higher than 13'6 and the bridge weight limits accomodate trucks.  Of course there are some exceptions, and many of the low bridges and restricted routes are listed in the Atlas, but they're not ALL there.

In some states, like New Jersey, most of the roads besides the interstate/turnpike, are not considered truck routes.  Many of the low bridges on local and state roads in NJ are not listed in the front of the atlas.  Sometimes, they're not even marked on the bridge itself, or they are improperly marked (i.e. the marked height was from before they paved the road, or sometimes the height is marked a foot SHORTER than it actually is, to compensate for snow in the winter.)  In these cases, it's best to get on the CB and ask other drivers for local information, ask people at the place you're delivering, and generally use caution on the road as you go.  

Most standard tractor-trailers are about 13 feet, 6 inches high.  Flatbed and automobile loads can sometimes be a little higher (some states allow up to 14 feet without a permit), but in those cases the driver is supposed to measure the load with a height stick before he goes down the road.  Not all low bridges are marked, but an experienced driver can usually tell if a bridge is "close" and should approach it with caution.  Car haulers will often stop, get out and measure the bridge height with their height stick, if they are unsure.  

The vast majority of bridges in the country are plenty high enough for trucks.  Most of the driving done by most truckers, is on the interstates and US Highways, where bridge heights are engineered for tall vehicles.  That's why you don't see more "stuck trucks"....it usually only happens when a truck driver has to come on a secondary local road to make a pickup/delivery, isn't familiar with the area, hasn't been warned about the bridge heights, and there isn't a sign warning him about the bridge (or the sign is inaccurate.)