Using junk science to sell new laws (1 Viewer)

[dennis63]

This week, the U.S. Department of Transportation announced an effort to regulate truck speeds. They plan to place control devices on new trucks to prevent them from going faster than a specific speed. (I believe it was 67 mph.) All the news organizations who covered the story quoted a DOT official's reason why this new regulation is necessary:

"Trucks take longer to stop because they're bigger and heavier."

What?

Obviously, the official is not a physicist.

Across the country, highly trained police officers, called "accident reconstructionists," are using physics to determine the minimum speeds of vehicles in fatal accidents. To be able to do this, they first attend a months-long course in advanced math and physics at Northwestern University. Most students don't make it, but graduates can testify as experts in court, and often retire and work for insurance companies. One of the things they learn is the "specific speed" formula.

Long story short: The formula uses the mass of the vehicle, the coefficient of friction on the road, and the length of skid marks to measure the speed needed for that vehicle to make that skid mark.

The secret? When you break down the math, the vehicle's mass ends up on both sides of the equation, and drops out.

That means mass is not a factor in braking. Big truck at 80 mph, small car at 80 mph. Same / same.

Big trucks take longer to stop because their brakes and tires are poorly maintained, or because some drivers are better than others, or because they are going faster than cars ahead of them in order to make the company's deadline.

I don't object to regulating the speeds of trucks, but I hate it when someone who should know better decides they have to "dumb it down" for the public. I hate it even more when the media -- who should know better, but doesn't -- parrots those things without questioning them.

Not long ago, we had the same claims about red light cameras: "They reduce accidents."

No, they don't. Put up a camera and you get fewer T-bone accidents, and more rear-end accidents as people slam on the brakes to avoid getting the camera ticket. The net is about the same number of accidents.

One rule of physics about red light cameras, though: More cameras = more tickets.

 

[DrStrange]

Maybe they might have argued that a higher mass truck will do more damage, though that might have been a better argument for lower load limits on trucks. Or they might have argued that slower speeds increases safety due to reaction times and less kinetic energy. All of that would apply to passenger cars as well as trucks. Maybe DoT has more jurisdiction over freight than passenger traffic? I can not help but feel that the old desire for lower speed limits to save fuel is not being reborn here rather than some newly born desire to make the roads safer.

Not only does the public lack scientific knowledge, but they are inundated with pseudo-science. This afflicts both sides of the political spectrum and a wide swath of religious teaching dressed up as science. Ignorance, disinformation and a lack of curiosity create a toxic brew that renders way too many people unable to tell truth from fiction. Asking a "talking head" or the production team behind them doing a news piece to know what they are talking about is asking the impossible. Instead the reporter(s) will find competing views and treat them as equals rather than one is right and the other is full of shit.

And they all get to vote -=- DrStrange

 

[Mental Nomad]

Long story short: The formula uses the mass of the vehicle, the coefficient of friction on the road, and the length of skid marks to measure the speed needed for that vehicle to make that skid mark.

The secret? When you break down the math, the vehicle's mass ends up on both sides of the equation, and drops out.

That means mass is not a factor in braking. Big truck at 80 mph, small car at 80 mph. Same / same.

This is right when it comes to skid marks - that is, when the tires have locked up. But that only happens if the brakes are stronger than the resistance the tires provide against the pavement.

But a heavily loaded truck puts more force on the tires, which creates more resistance... If the truck is heavy enough, it can be more resistance than the brakes can handle, even when properly maintained. So a very heavy truck's tires don't all lock up, even when the brakes are on full...and it can take much longer to stop.

 

[Mental Nomad]

Long story short, brake horsepower matters.

 

[JoseRijo]

The secret? When you break down the math, the vehicle's mass ends up on both sides of the equation, and drops out.

???

Dude, F = MA. The M is 'mass'. It doesn't cancel out.

 

[legend672]

???

Dude, F = MA. The M is 'mass'. It doesn't cancel out.

"Mass" achusetts

 

[dennis63]

???

Dude, F = MA. The M is 'mass'. It doesn't cancel out.

Yes, F= ma, (Newton's second law) but that's only half of what you need to calculate the stopping distance of a vehicle. The other half is Work (force over a distance, or Fd)

A vehicle is traveling at speed. It stops because the brakes have done work equal to the forward force of the vehicle.

The formula actually used, derived from F=ma is:

ma (d) = 1/2 mv (squared)

Divide both sides my Mass, and you get a(d) = 1/2 v (squared)

Multiply both sides by 2, and you get 2a(d) = v (squared)

Mass is not in there anymore.

Mass appears on both sides, so you divide both sides by Mass. It cancels out. You actually "take it out" of both sides.

Heavier vehicles have more mass moving forward, but also push harder against the ground due to gravity.

It is counterintuitive to think that the mass of a big truck moving forward will work to stop the vehicle when you hit the brakes, but it is a fact.

I took a shortened version of this class long ago. I wasn't cut out for Northwestern. But I do remember this:

The reconstructionists taught what they learned from physicists. They noted that a big truck and a little car at the same speed take the same distance to stop.

Again and again they told us the mass of the vehicle doesn't matter. If a big truck took too long to stop, something was up with the brakes.

 

[Chicken Rob]

What about ABS, big vented break rotors and big tires. F1 cars break way faster than passenger cars. So do Ferraris (I got to drive one once).

More surface area with the road and with the break rotors and more controlled force to the breaks seem to yield better stopping distances. Let's legislate cars and trucks to brake better.

 

[slisk250]

Get big oil involved. They want those truckers hauling ass and burning petrol.

 

[Lil Tuna]

Hey everybody,
Just a little more info to add to all the equations here. If you know anything about tractor trailers, they actually stop quicker with heavier loads. It's called air brakes and they do a great job stopping heavy vehicles. Make no mistake, at the end of the day any governing body doesn't give two CHIPS about your safety. What they care about is revenue. If they can create a law that can be broken so they in turn can write tickets and collect fines, they'll do it. I suggest the next person on here figure these angles into the next equation they come up with.
But hey everyone, I love the chips and trades and cool stuff people have on this site. I completed an awesome collection of my own buying and trading here on PCF.
After driving tractor trailers for 25 years and having over a million safe driving miles, PCF is the last place I figured I'd learn why the government wants to limit the speeds of big rigs. Hey guys, happy chipping to ya. Learn something new everyday.

Cheers,

Tuna

 

[stocky]

Speed limiters are in place on some heavy vehicles in Australia.

Ask any truckie here who has one and they will tell you they are probably more dangerous. There are plenty of videos on YouTube of what happens when a truck is behind a slow vehicle and can not pass due to being able to bring the truck to a higher speed to overtake.

 

[Quicksilver-75]

Sorry Dennis. Your kind of wrong here. I'm a driver and I have been a long time. You haven't taken into consideration a few things. If heavy transport trucks brakes were hydraulic like an automobiles your science would still be off. As it happens they are obviously air brakes. Meaning they use compressed air to actuate a variety of set-ups. Using air brakes is the standard because of the mechanical advantage it offers large vehicles. But there are just few things that come into play.
The first is a thing called Brake Lag: this is the time it takes for the truck (and trailer) to even BEGIN to slow after the driver has touched his brakes. The distance at 55 mph on dry pavement adds about 32 feet. So at 55 mph for an average driver under good traction and brake conditions, the total stopping distance is over 450 feet.

The second is a thing called Brake Fade: This happens to all vehicles but is most noticeable in trucks. The heat and gasses generated during a heavy application will actually impede the brakes ability to slow the truck (and trailer) thus after some time rendering them virtually useless. If you've ever wondered why the Blue Ridge Mountains have those tractor runaway lanes that go uphill brake fade is your answer. It is also why truckers will use a lower gear or two to avoid riding their brakes.

I will agree however on the poor maintenance aspect. This has become a huge problem ever since the industry (in Canada) moved away from fleet-run to owner-operator. The pre and post trip are rarely done properly and preventative maintenance just isn't performed. It is my opinion that absolutely truck traffic should be held to slower speeds. Moreover there should be more enforcement to keep tractor trailers to the right on highways, limit passing and use manditory training periods to educate today's young, inexperienced drivers about the #1 issue in the industry: stopping distance/tailing.

 

[trever]

I'm imagining the fun I'll have getting stuck behind a speed-governed 67mph truck passing a 66mph truck on a 75mph speed limit highway.

 

[Quicksilver-75]

I'm imagining the fun I'll have getting stuck behind a speed-governed 67mph truck passing a 66mph truck on a 75mph speed limit highway.

Well the small amount of time it takes for you to safely pass said vehicle is a smaller inconvenience than having to cut your family out of the empty beer can your car has effectively become because the truck 100 feet behind you is traveling 75+ and still needs another 550 feet to not KILL you..

 

[Lil Tuna]

Just completed a great set of WTHC chips. Thanks to The Kid, Moontaffy, Bigfruits and Roger from Canada for helping me fill in the missing pieces. Love the PCF.

 

[pltrgyst]

A better title for this thread would be "Using Junk Science to Argue against a New Law."

The argument presented to you, Dennis, conveniently ignores highly relevant factors, such as the distribution of the trailer load, the designed stopping ability of the brake system, the size of the tire contact patches (which is highly dependent on tire pressures), and the hardness of the tire rubber.

Removing mass from that equation is simply a way of determining the relationship of other factors *for a given mass*. It does not mean that differing mass is not a factor in a vehicle's relative ability to stop.

I'd love to see 18-wheelers submitted for Car & Driver's standard 60-0 braking test, both unloaded and fully loaded.

Or if you have faith in that bogus "science," just do a real-world test: take a loaded 18-wheeler, in perfect mechanical condition. Have someone -- a really good driver -- drive it, two car lengths behind you, driving a 2500 lb. Miata, both at, say, 70 mph. On a given signal, you both nail the brakes. Let us know how that turns out.

 

[Lil Tuna]

Had a great session at the 1-3 in Baltimore over the weekend. Didn't get run over by any speeding commercial vehicles on the ride up and back. Happy chipping to you chippers. Can we save the politics for the CNN site? Just here to embrace poker related things. I can get my fill of government indoctrination when I turn on my television. May all your cards be live and your pots monsters everyone.

 

[jbutler]

View attachment 54196 Just completed a great set of WTHC chips. Thanks to The Kid, Moontaffy, Bigfruits and Roger from Canada for helping me fill in the missing pieces. Love the PCF.

View attachment 54197 Had a great session at the 1-3 in Baltimore over the weekend. Didn't get run over by any speeding commercial vehicles on the ride up and back. Happy chipping to you chippers. Can we save the politics for the CNN site? Just here to embrace poker related things. I can get my fill of government indoctrination when I turn on my television. May all your cards be live and your pots monsters everyone.

Hey, @Lil Tuna. Welcome to PCF. Great pics, but there are subforums and threads more appropriate for this sort of content where they can be posted without being off topic within an irrelevant thread.

For your World Top Hat & Cane chips, if you're interested in starting a thread, here's the Poker Chip Pr0n subforum. For your Horseshoe stack, here's a thread devoted exclusively to live stack pr0n. Enjoy!

 

[Lil Tuna]

Thanks jbutler. Hey I enjoyed reading about your trip to Parcs over the weekend. 4-8 hand all D flop. Just trying to lighten up the subject matter over here. Hope you turned that into a good session.

 

[Poker Zombie]

It is my opinion that absolutely truck traffic should be held to slower speeds

Unless the truck is carrying a shipment of new chips to a chipper - then it's FULL SPEED AHEAD!!!

As an aside I have taken out a brand new, fully loaded firetruck (with 750 gallons of water) into an empty parking lot. I got it up to 30 MPH, locked up the brakes and was astounded at how short the stopping distance was, at around 60'. I have not taken a passenger vehicle on the same surface to try the same test, as it wasn't about science as much as it was understanding the limitations of a new apparatus.

However, brake fade is a very real concern that can greatly diminish a truck's ability to stop as quickly as it could with cool/fresh brakes.

 

[pltrgyst]

View attachment 54197 ...Can we save the politics for the CNN site? Just here to embrace poker related things. I can get my fill of government indoctrination when I turn on my television.

Who appointed you den mother? I didn't realize you could achieve that distinction after only 29 posts.

This forum's title is "Off Topic." That means you're not likely to find any "poker related things" here to embrace. If you don't like the subject -- or after reading a post or two, the direction of the conversation -- stop reading the thread.

Signed,
-- Crabby Appleton

 

[Lil Tuna]

Hey guys, I'll agree that east of the Mississippi River trucks should not travel more than 65-68 mph tops. But if any of you have driven out west in places like Texas, Utah, Arizona etc etc, 70 mph for any vehicle is like crawling.

 

[Lil Tuna]

I hear you Crabby. LOL. Hope your trip to Aruba was or still is great. Enjoyed your pics and posts.

 

[David O]

I am in the trucking business in Texas. We govern our trucks to 65. No need to go any faster with hazmat.
In this industry there are many laws. Some make sense and others do not. One I will point out is DEF fluid. What a crock. It is over 67.5% water and the rest is Urea which is a byproduct of mammal piss. The only things this fluid has done to the industry is add weight, add more truck down time and increased operating costs. Like piss and water really cleans the emissions.

Oh well there was my "off topic" rant!

David O

 

[jbutler]

It is over 67.5% water and the rest is Urea which is a byproduct of mammal piss.

Can't believe I've just been flushing my valuable mammal piss for years now.

 

[Forty4]

Can't believe I've just been flushing my valuable mammal piss for years now.

Honey, don't flush these bottles, I'm supplementing our income and saving the planet by recycling. You can do your part to help out I'll give you your own container.

 

[abby99]

I am in the trucking business in Texas. We govern our trucks to 65. No need to go any faster with hazmat.
In this industry there are many laws. Some make sense and others do not. One I will point out is DEF fluid. What a crock. It is over 67.5% water and the rest is Urea which is a byproduct of mammal piss. The only things this fluid has done to the industry is add weight, add more truck down time and increased operating costs. Like piss and water really cleans the emissions.

Oh well there was my "off topic" rant!

David O

I like to learn something new every day. I wasn't today's new information would be about re-purposing mammal piss!

 

[dennis63]

Or if you have faith in that bogus "science," just do a real-world test: take a loaded 18-wheeler, in perfect mechanical condition. Have someone -- a really good driver -- drive it, two car lengths behind you, driving a 2500 lb. Miata, both at, say, 70 mph. On a given signal, you both nail the brakes. Let us know how that turns out.

OK!

Hey, can I borrow your car? Mine is in the shop getting a radio knob replaced.

Many useful and intelligent comments here from professionals about why trucks do take take longer to stop, though.

 

[Poker Zombie]

I'm also going to add the possibility of a truck jack-knifing when panic braking occurs. This can shut down an interstate for hours, costing 10s of thousands of dollars (more if the materials spilled are eco-dangerous). This is not so much of an issue with smaller vehicles.

It doesn't justify using psuedo-science to pass a law, but as America is so far behind the rest of the industrialized world in matters of science it may be the only science we can understand.

 

[DrStrange]

I can't believe there isn't some real world measurement data rather than theory to guide this discussion. Reality generally doesn't match theory, though it is often close.