How long does it take a truck to stop & is it criminal if he doesn't?

Page 4 of 7  
Unquestionably Confused wrote:

Factors effecting stopping distance:
http://www.crashforensics.com/truckcrashreconstruction.cfm
As far as stopping distance requirements:
http://www.ttnews.com/articles/basetemplate.aspx?storyid "391
It may have changed, but when I took the CDL test, the official view was an empty truck would take longer to stop.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

He was going downhill so you have the sign wrong, it should be f-G for this case. That's not a big difference and not your major error. Your major error is thinking that truck tires and truck brakes will come close to the maximum available surface friction of the pavement. For estimating purposes a more realistic effective coefficient of friction would be 0.50. Crunching those numbers gives you around 230 feet.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 11 Jul 2014 19:30:48 -0500, Unquestionably Confused

In the real world it would not be immaterial. The empty truck with it's 120psi tires and stiff springs would most likely "bounce" around if the wheels locked which would greatly increase the stopping distance. OTOH, a fully loaded truck might not even be able to come close to locking all the tires or even doing a good job of "braking" them so it too could have long stopping distances. But it extremely unlikely the stopping distances would be the same, in the real world.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

which will stop faster than an overloaded truck.
The load rating of a truck takes into account the tire load rating, the axle load rating,the spring load rating, the braking capacity, and the horsepower and gearing of the prime mover. If there is no Or not enough) weight on the braking wheels, the truck will slide. If there is enough weight on the braking wheels, the tires will hold. If the tires hold more than the brakes, the brakes will limit the stopping distance. If the brakes hold more than the tires, the tires limit the stopping distance. If the brakes and tires are adequate to stop the load, you stop in time. If they are not adequate to stop the load, you do not stop in time. Required Brake horsepower on a grade is determined by the distance travelled in feet times the weight being stopped (ft lbs) devided by the time required to stop it devided by 33000. 1 HP is 33000 ft lbs per minute. So to stop the descent of a 40,000lb truck on a 100 foot high hill hill at 60 MPH in 1320 feet (1/4 mile) over stopping the truck on the level, requires the addition of approxemately 757 HP of braking force. The same amount of extra power it would require to acclerate the same load from 0 to 60 up a 100 ft hill over a quarter mile, over just accellerating it on the level. Double the weight, double the required horsepower. Double the speed, double the horsepower. Double the incline, double the horsepower. Just accellerating, (or stopping) that 40,000 lb truck on the level requiers 475 HP 0-60 or 60-0 in a quarter mile in 25 secconds. Increasing the load to 60000 lbs raises the power required to 715HP Increasing the load to 80000lb requires 950 HP.
SO Lets stop a 40000 lb truck from 60MPH to a dead stop on a 100 ft high 1/4 mile long hill. The brakes will have to dissipate 1232 HP. Double the weight of the truck and the brakes are required to dissipate 2464 HP.Double the incline and the 80000 lb truck requires 3221 HP
Now, not only do we need enough brake to absorb that much Horsepower, we need enough tire to put that 2464 HP to the ground without breaking traction with the road surface. The number of tires on braking axles most definitely comes into play here. (as does the number and capacity of wheel brakes available) - because as stated before, stopping distance is limitted by the lesser of brake power and tire traction.
In the case referenced by the OP, the tires ran out before the brakes as the trailers slid and jacknifed - and if the tired HAD been able to hold all of the braking force, the brakes most likely would still not have been adequate to stop the loaded truck in the time/space allowed from the speed he was going.
Reducing the speed coming into the situation reduces the required braking power for both the decelleration of the load and the control of descent of the load much more than the weight by both reducing the feet per second AND increasing the time/distance available to stop.
Increase the load by 10%, reduce speed by 5% - more or less for the same stopping distance.
I likely missed a few factors that will skew the numbers slightly - but theyw are close and show the "trend"
Weight and tires/brakes as well as speed all have a BIG effect on stopping distance.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ashton Crusher wrote, on Fri, 11 Jul 2014 22:43:24 -0700:

The first article in the OP says that the driver, Ravinderbal Singh, said he jammed on the brakes, which began to smoke, but did little to slow him down.
He's quoted as saying "It wasn't decreasing speed. It kept going up 'cause it was, like, too steep for me,".
Does that indicate the tires or the brakes were the limiting factor in his inability to stop until he had crushed the 10 cars in front of him?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jesse Davis wrote:

The actual limiting factor was gravity.
The smoking brakes means that he had been using the brakes coming down the grade, they started to heat up (which is what they do, convert the kinetic energy of rotary motion into heat energy through friction) Want to demonstrate this, take DRY hands and rub them together rapidly, what happens? They heat up.
Now in this case the brakes were already heated from the earlier usage, When he "jammed" on the brakes the heated shoe surfaces started to outgas. This is common and actually normal to an extent. Basically the binder material that glues the friction material together gets heated and small amounts of gas/smoke are released. After the first few NORMAL stops heat the brakes up the process slows because the heat levels never rise much more.
In a panic stop the brakes create far above normal friction, the heat rises VERY rapidly and the shoes try to absorb the heat and try to release the heat into the air. The drums also get VERY hot and they try to dump the heat into the air as well.
While this is happening the gases from the brake shoes actually act like lubricant, that destroys the friction coefficient. The remaining friction keeps heating things up in a vicious cycle.
What the CHP will do is go over the drivers records. Then the trucks records, including ALL the paperwork. They will look at the weight ratings of the components as well.
Those ratings will be a key item. Every vehicle on the road has brakes engineered to stop a given weight. Basically they take the GVWR and calculate the amount of braking force that will be able to stop that weight in a given distance at a given speed while still maintaining control of the vehicle. Then they add in a safety margin to cover some misuse/abuse and unforeseen circumstances.
Most big trucks have brakes far larger than they actually need, BUT it is also possible that they don't.
--
Steve W.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 11 Jul 2014 19:30:48 -0500, Unquestionably Confused

I question that. I would expect the one with concrete to have far more inertia to overcome than the one that is empty.
--
"Pulled pork tacos.
"Greasy, messy, pulled pork tacos."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The truck would have stopped faster. It has air brakes.
SH
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/12/2014 7:31 AM, Sherlock.Homes wrote:

Brilliant deduction!
--
.
Christopher A. Watson
Learn about Jesus
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/12/14 6:31 AM, Sherlock.Homes wrote:

Air resistance wouldn't have been a factor.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 11 Jul 2014 18:53:13 -0700, Evan Platt wrote:

I believe I had asked if the skirting was required by law. As I had not seen skirting like this on trucks while I was an active driver.

I may have. But then also said something else to clarify and you never mention that.
If you have a CCW in state A, you can carry that firearm all you want. Cross the line into state B, who does not issue CCW, and you could go to jail. You can carry a firearm in a ttuck as long as it is properly locked and stored and not within arm's reach. But if you work for a company and the company owns the truck, when they find that firearm, they can and will fire you if they do not allow firearms.
You're the one who is a frickin laughing joke. Claiming to be an expert on any topic.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 11 Jul 2014 21:54:09 -0500, deadrat wrote:

Actually that was Jeremy Clarkson on "Top Gear". Two different things. When on the moon, Neil Armstrong dropped a bowling ball and a feather at the same time. Both landed at the same time. That works in a vacuum.
And the real experiment was done using a ramp. With various sizes and weights of balls.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I think you're confusing theory and practice. Brakes can overheat, slip, or otherwise fail under enough stress.
I once saw a freight train derail. It was amazing how far the fairly slow moving train moved while off the tracks and wheels sliding along the rock train bed. Momentum is a serious force.
--
Dan Espen

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
trader_4 wrote:

I recall from freshman physics that the mass normal to the friction surface and cancels out the kinetic energy. Of course, they professor also said the coefficient of friction couldn't exceed 1.0. A new explanation was needed when the fuelie dragsters started posting E.T.'s and terminal speeds that didn't compute.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Saturday, July 12, 2014 10:40:10 AM UTC-4, rbowman wrote:

I think the issue here is that the physics are based on certain assumptions and we don't know how well that conforms to what happens with a truck in the real world. The friction force is what's key. We know that the energy of the truck goes up proportional to the mass. The physics of the friction says that it too goes up proportional to the mass, but there must be some set of assumptions along with that. The question is how closely the truck tires fit those assumptions. What works for friction of a piece of sandpaper going across concrete with a 5lb or 10lb weight could be different than what happens with a hot truck tire.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

Generally a Prius that somehow overlooks a 65' long, 13' high 78,000 vehicle with a bright red paintjob and pulls out in front of you. There's also the BMW Z3 piloted by a Master of the Universe that really thinks he's going to win a game of chicken with a Volvo White.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
richard wrote:

The driver trainer at the company I worked for explained that the company policy forbade firearms in the trucks but common sense suggested a 9mm close at hand was a good idea. A couple of times I had to go to Canada and left my firearm with the terminal manager. Nothing was said.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@snyder.on.ca wrote:

I imagine ABS has improved a lot, but a bobtail had all the stopping power of a skateboard. Mostly the drivers were rolling or they were locked up unless you were very gentle.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Bullshit.
Newsgroups: misc.transport.trucking Subject: trailer side skirting ??? Date: Sun, 3 Oct 2010 14:58:03 -0700
"What's up with trailers having plastic or canvas skirting between the wheels? I've been seeing more and more of them with it."

Maybe because you don't pay attention?

No, others clarified.

ROTFLOL.. How's that dome home coming?
<crickets>
--
To reply via e-mail, remove The Obvious and .invalid from my e-mail address.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.