How do truckers know clearances in advance?

I saw an item on the local news today about a truck whose load hit an overpass. I know that truckers are responsible for knowing how tall their loads are, but how do they know in advance whether it is safe to carry a particular load on a particular highway? Overpasses have their clearances marked, but by the time a trucker sees the marking for a low overpass it’s a bit late to do anything about it.

Are their standard minimum clearances for different types of highways? If so, are there exceptions? How would truckers know where the exceptions are?

There are special atlases made that indicate clearance for overpasses, along with alternate routes for overheight/overweight trucks.

No great mystery there. :slight_smile:

Robin

TxDOT currently requires a 16.5’ minimum clearence and prefers a 17.5’ if possible. AASHTO (the American Association of State Highway and Transportation Officials) requires a 16’ vertical clearence on highways and interstate systems “where such clearence is not unreasonably costly and where is needed for defense requirements” The absolute minimum vertical clearence required is 14’. It’s the older bridges that have lower clearences (it’s a particular problem with old arch bridges where they’ve added lanes below the arches).

Couldn’t find a cite but I think the average semi is around 13’ high. It’s the guys with the weird oversize loads that have to be careful and they have to know what clearence they need and map out a route.

On two occasions, I’ve seen a trucker get in trouble (and they were all old bridges). In Atlanta, a trucker didn’t move to an inside lane on a road that passed under an old stone RR bridge. It peeled open the trailer like a sardine can. And on the Univ of Tex campus, they needed to bring in construction equipment (a really big crane) to a site just past a pedestrian bridge. They could’ve taken a really long way around but they chose to let air out of the tires and inch it under. And, actually, my ex-boss was at a bridge on a country road taking pictures so we could interview for a replacement, and a car carrier truck came flying by, didn’t have enough clearence and scraped a couple of Suburbans off the top. He had some great photos but we still didn’t get the job…:frowning:

You buy a book with this stuff, which you can find at any truck stop. They are quite expensive.

I know someone who used to tour with Sesame Street Live. He said that New York has some tight regulations on the size of trailers, so they would regularly get new trailers and repack when going into New York. Why they didn’t just go to a lowest common denominator beats me.

When I lived in Worcester, MA this was a constant problem. Semis would regularly get themselves tin-canned on the overpasses in town. On one memorable day two semis did it on the same day creating an unreal traffic jam that paralyzed the city.

The explanation I was given was that truckers would cut the clearances very close. With our hard winters the huge frost heaves would change the pavement and repaving could take away several inches that were there before, or were indicated on the map. I remember many clearances marked at 13’6" so that would make sense if one was driving a 13’ semi.

Do you Americans have those “wind chime” type things hanging from an overhead gantry?

An example of this is Sydney’s motorways. The toll booth plazas have a roof of a certain height. There is an unroofed outside lane for overheight vehicles. A couple of hundred metres before the plaza, there’s an overhead gantry that has, above each lane, several hollow aluminium tubes hanging down vertically from a length of chain. The bottom of the tube is the same height as the roof of the toll plaza. If the truck is overheight, it will hit the tubes and make a hell of a racket - but little or no damage (as opposed to hitting the plaza roof). This gives the driver time to get into the special overheight lane. The tubes are a last resort, of course. There are plenty of “4 METRE LOW CLEARANCE AHEAD” signs beforehand.

Is there a technical term for these “wind chime” things?

In some cases, particularly where uversized loads that require special permits are required, the proposed route is run with a “pilot car”. This is usually an automobile or pick up truck with a mount and adjustable height pole mounted on the front. The pole is adjusted to the load height and the pilot car runs the route. He then knows where any problems might occur and can make note of any power lines etc. that might have to be moved.

I work at Boeing in St. Louis and two years ago they were planning to have some new machinery shipped in from someplace up North. I happened to be out on the parking lot when the pilot car driver was checking his paperwork for the move.

He said the various states have departments that issue the permits. You tell them the size of the load and they tell you the route to take. but they sometimes make errors and that’s where the pilot car come in. In this particular case the proposed route went under a railroad bridge about 1 mile away, and the clearance was about 6" too little. due to familiarity with the area I was able to suggest an alternative route. So he want off to check it out.

The permits go so far as to sometimes limit the times you can be on the road as well as the route to be followed. Sometimes they might have to remove and reconnect powerlines and traffic sighns too.

And let’s not forget the idiots who don’t take the “no commercial vehicles” signs seriously. In Manhattan, there are two major highways - both of which are off limits to trucks. The one running down the east side of the island (the FDR) has low overpasses about every mile or so. I can’t count how many trucks I’ve seen who ignored the warnings and wiped out.

The best was a truck full to the brim with those little (12 inch) round watermelons. Not only did it wipe out, but every car that got hit by a watermelon wiped out, and every SUV that hit the smushed residue of a watermelon SLID and wiped out. Only the SUVs, presumably because of their greater inertia. When I went by (going the other direction) there were around 15 SUVs, two cars, and the truck looking forlorn, the road was closed, and they had brought out the local street-cleaning equipment to clear the smushed watermelon. Quite the scene.

I’ve heard them called “loading gauges”. This seems to hold true for rail transportation, in the UK at least (picture near bottom of this page).

I’ve witnessed two “only in San Francisco” equivalents to the low-bridge wipeout, both involving long-wheelbase vehicles on Russian Hill. The first was a super-stretch limousine attempting to go down Lombard Street, getting stuck"side-to-side" in the landscaping, and having to be pulled out backwards by a tow truck, much to the amusement of the tourists on the cable cars going past on Hyde Street. The second was the “grounding” of a truck on Taylor Street between Green and Broadway— Taylor goes up the hill at a steep angle, makes a sharp transition to flat, then steeply down the other side. The truck made it up the hill, and had its front wheels on the level part while the back wheels were off the ground on the hill part, merrily spinning away. I didn’t stay around to see how it was eventually freed from its predicament…

The general rule in the US is that 13’6” is the highest allowed on US interstates, length however varies from state to state. In the north east trailers over 48 feet should be the maxuim length but in Texas and the west coast 53’ trailers are common.

Federal width, length, and weight laws:

WIDTH: The Federal law mandates that every state allow a maximum of 102"in.
If the state doesn’t permit up to 102"in. wide vehicles to travel on all
interstates, & some designated highways, it could lose Federal highway
funds.

LENGTH: The Federal law (sec.411) mandates that every state allow a minimum
of 48’ft for single trailers, 28’ft each for double trailers. A maximum 53’ (57’ft in some states) for single trailers. This law overrides the state laws
establishing limits less than 48’ft for interstates,& some designated highways.
No state is allowed to set tractor length limits.

WEIGHT:The Federal law (sec.133) mandates that every state must allow a
maximum gross weight of 80,000#lbs(40T) or lose Federal funds.

Mischievous, remember not every one is from New York and the streets are narrow and confusing at best for someone not from the area. Manhattan is a mess and the FDR seems like a good way for someone to get out of the city looking at a map (which most have no indication of “No commercial vehicle” and with the many one way steets its very hard to get turned around in one. The LIE for one is tricky and at one point there is a sign that says 12’11” and I jammed brakes only to have another truck pass at speed saying the sign has been wrong for over 5 years now.

Antonius Block, San Francisco presents its own challenges since it’s not the low bridges that cause most grief but the hills have a very sharp break over angle which can cause you to “high center”. No maps show this so it’s usually the driver to determine if he can make it or not. The break over varies as a freight container has a lot of clearance but a moving van is usually lower to the ground between the rear tandem axles of the trailer and tractor. This happens a lot railroad crossings are notorious for hanging up trucks but he was most likely pulled backwards of by a large tow truck. The sensors that hang down to detect over height trucks are usually used at weight inspection stations and toll plazas and sometimes before tunnels that have a very close height to 13’6”

As mentioned before roads get packed with snow, repaved a various other things happen and sometimes the sign isn’t changed so the driver assumes he has enough clearance.

There’s a 10-foot overpass here in town (railroad tracks on top of it) that gets hit by a truck every two months or so. The streets a block to either side are grade crossings, so it’s not like they don’t have a choice. The latest one was a flatbed carrying lumber; it hit the bridge and sheared the top two feet of 2x4s off and scattered them all over the road. Took a few hours to get it all picked up.
My dad used to be a trucker (in the '70s). Once he had to get past an overpass that was an inch too low for the bulldozer he was hauling, and had to stop, let some of the air out of every tire, drive under, and stop on the other side to refill all 18 tires.

Oh, I know. I have nothing but sympathy for truckers trying to drive around the one-way streets and squeeze past the innumerable double-parked cars. And, while I don’t know about map markings, there are entrances to the FDR which I don’t remember seeing “No commercial vehicles” signs at. However, most of the entrances are clearly marked, and I have seen numerous trucks enter on ramps that had no less than three warning signs and an easy turn-off to use as an escape route. I’ve made sure to get well ahead of them before the first overpass, because at least two have wiped out (and a third would have, except it was 4a.m. and traffic was light enough that he could pull over).

Not knowing the roads is excusable (although I would hope that trucking companies try to send New York-experienced drivers here). Not paying attention to the signs is both illegal and STUPID.

mischievous