[donald]

Why Shouldn’t Someone “Brake Check” a Semi?


@metastable
Why have you managed to draw the completely wrong conclusion, yet again?

 

[donald]

My girlfriend took it last night while I was driving. We’re on a 2200 mile road trip. It’s a general public safety announcement— when passing a semi, don’t switch lanes right in front of them and then tap your brakes. If you look closely you can see a car on fire right in front of the semi.

There is no suggestion that happened as far as I can see.

The debris field appears to be on the hard shoulder. Looks like a case of a sleepy truck driver crashing into a stopped car.

 

[donald]

Well we were driving through rural nebraska and while doing 80mph+ I was getting passed by semis doing 85+mph. Most of them were doing about 80mph.

That'll explain it better, wouldn't it?

I suspect the truck might have suffered tyre blowouts, given the flaming marks on the road.

Allowing trucks to drive at speeds in excess of the speed ratings of the tyres seems to be a peculiarly North American thing. They do that in Arizona too, and there the tyres are also under a higher heat loading.

Maybe don't jump to conclusions.

 

[donald]

If a semi hit a parked car it’d most likely be an offset collision and the car wouldn’t have ended directly in front.

View attachment 137748

Draw me the diagram showing the semi squarely in the hard shoulder as the guy was asleep. What happens then?

Then draw a diagram of someone hitting their brakes in the 1st carriageway lane, where do they end up after 'that' crash ... all neatly on the hard shoudler? errrr ... I think not ....

How can a truck hit a car in the 1st lane and after everything stops they're both on the hard shoulder? Draw me that diagram, please.

 

[donald]

AP will brake check whom it damn well pleases!

Yup...

Ahh.. the marvels of a self-driving car ...

 

[donald]

We're moving into a new era where people really will have to keep their distance.

There is no point tailgating another vehicle and flashing lights at them if it is on auto-drive-pilot-somethingorother as if it will have any effect on the 'thing' in control of the car. It'll happily slam on the brakes if it passes something a bit close, so you'd better be aware of that.

 

[donald]

On the other hand if you are driving a truck and tailgating, it would be the occupants of the car on AP who need to worry.
Another little supervisory duty for the "relaxed" person who would otherwise be driving.
Might as well drive yourself!

Yup.

 

[donald]

I don't know about ACC in trucks.

However I do know that truck braking distances are MUCH longer than cars.

That is not strictly true, until recently. The requirement up to a few years ago was a stopping deceleration of 0.5g for both trucks and cars. The fact that a brand new modern car 'can' stop quicker was not a requirement, although new homologation has put that to 0.7g or so, I do not quite recall.

The issue is the performance of the road. Those numbers above are the perfect performance of a tyre/wheel without slip and relates only to the braking performance of the chassis systems. An articulated truck needs more space because it will very rarely be in a dead-straight braking event (even along a motorway, as the driver will probably attempt to steer around an obstruction first), and if it is in a slight bend it will need more space for the braking to be dynamically controlled. ABS on the rear axle of a tractor unit has been a requirement since, I think, 1987, for good reason. I am not sure if ABS is actually required on modern cars, still?

 

[donald]

Half of those accidents aren't caused by brake checking someone but general stupidity.

The US propensity for allowing vehicles to weave between lanes overtaking and undertaking is one cause.

They don't allow it any more than UK allows it. But it happens in both places.

US is more relaxed about passing to the right, but it is not meant to be 'for overtaking'. It is assumed everyone is driving in their lane at the speed limit.

 

[donald]

In California on Interstate 5, the semis have a 55mph speedlimit (and go 62mph) whereas the cars have a 70mph speed limit and go 80mph. But in Nevada / Utah / Wyoming / Nebraska, everyone has an 80mph speed limit and the Cars as well as semis all go 80-85mph, which seems more dangerous.

It is dangerous.

I have never seen an HGV tyre with an adequate speed rating for that.