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Semi attempts U-turn on main downtown Denver arterial


Downtown traffic was blocked at Colfax Avenue and Bannock Street for about an hour this morning after a semi-truck became stuck, blocking lanes in both directions.

Around 7 a.m. the semi was traveling on E. Colfax Avenue [I think it was traveling eastbound on West Colfax - RG] when the driver attempted to make a u-turn onto West Colfax Avenue at Bannock Street, according to Denver Police Officer Dan McNulty.

The semi clipped an air brake, causing all of the truck’s brakes to lock up, stranding the semi across Colfax Avenue.

West Colfax Avenue was closed at 15th Street and traffic was being re-routed. There is one lane open on East Colfax Avenue.

A tow truck had to remove the semi, McNulty said. The road was cleared shortly after 8 a.m.

The driver likely will be cited for making an illegal turn.

Could trailer brakes not have been manually released in a few minutes?

No, trailer brakes can’t be manually released because they require air pressure to release. Semi brakes work the opposite of cars - in a car when you step on the brake, hydraulic pressure is increased on the calipers and that makes them squeeze the rotor. In semi air brakes, the brakes are on by default, and require air pressure to be released.

So if you clip an air line, the brakes lock up, which is better than the alternative of a 40 ton semi with no brakes charging through town.

Yes. This is also the same way train brakes work.
Releasing train brake line pressure applies the brakes according to the pressure reduction.
If the train uncouples, the brakes automatically fully apply.

Railcar brakes can be manually released, (closing brakeline valve at each end contains brakeline pressure in the car’s brakeline?) and the brakes and can be manually applied with the brake wheel on every car.

But I thought a semi-trailer’s brakes can be manually released using a socket wrench.

I gather this is done as a safety measure: having the brakes’ default setting ON prevents runaway in the event of total air pressure failure.

So why isn’t this done on autos? Despite hydraulic fluid vs. compressed air, it doesn’t seem unworkable: constant hydraulic pressure keeping the brakes off, and pressing the brakes bleeds off some of that pressure, allowing the brakes to revert to their default “on” setting.

With dual redundant braking systems, we don’t see much total brake failure in autos, but I HAVE seen several “rollaways,” which would be almost impossible with “default on” braking. This would also prevent people from trying to “limp home” vehicles with half the braking system non-functional–they’d be stuck with locked wheels.

Would require a pump and pressureservoir.
Rail cars with brakes not manually applied have leaked off enough air over time thathey have started to roll.
Could that happen with hydraulic fluid pistons?

If one could then you would have a rolling tractor and trailer combo with NO BRAKES. Let it sit and wait for the wrecker. If it did start rolling then you could pull over into an oncoming lane and risk a head on with an innocent traveler, but the truck driver would appreciate it.

You disconnect the trailer brake lines and the tractor’s independent brakes do the braking.
Actually, if it could not stop, it could move into the back of my vehicle and my four brakes would help stop it, especially if the back of the car gets wedged under the truck’s bumper and rubs on the pavement. Saw that happen in Michigan.

It’s easy to manually release an air brake on a big truck. All it takes is a 3/4" wrench. With no air to the chamber, spring pressure applies the brake. A threaded “caging” tool is inserted into the spring and a nut is tightened down against the outer edge of the chamber, compressing the spring and releasing the brake. All spring brake chambers have a caging tool attached to them when new. It’s perfectly safe to release all four trailer brakes and move the truck & trailer off the road using just the tractor brakes, and way cheaper and quicker than waiting for a wrecker. In addition to a ticket, the driver in this case probably spent at least $400 for the tow. An even easier way would have been to swap the cut supply air line with the undamaged service brake air line, which would take about three minutes and allow the trailer to move, albeit with no trailer brakes again. Still, much quicker, cheaper, and easier.

Thanks you, <>Chevy.
That’s what I thought.

So instead, Denver Police keep a vital downtown arterial closed for an hour during rushour?

I’ve been a tractor trailer owner/operator for 27 years. To succeed in this business, it’s mandatory to be able to get yourself back on the road after a breakdown, and quickly, as Johnny Law will not wait long before writing tickets or calling a hook. Unfortunately, many O/O’s new to the industry, and most company drivers, don’t know much, if anything, about the mechanical aspect of the truck they’re driving. So, they end up with a complicated and expensive mess like the one described here when some basic knowledge could have saved all involved a lot of time and money.