REVscene Automotive Forum - Anyone good at physics? 70km/h car crashing into 70km/h car...what will happen?

As many of you know, there's a video called Speed Kills Your Pocketbook, the video that shows the safest speed to travel is go at 85th percentile.

Anyways, the officer says 70km/h car crashing into 70km/h car will be totalling 140km/h of force.
The video editor responds that's false. Then officer responds that My Buster is wrong.

So what's the real answer???? :confused:

The officer appears at 7:50

Here's the website that shows this conversation: Increasing speed limits is not a death wish

What officer wrote:

January 19, 2015
What really gets to me is that you pass judgement on me without ever speaking to me.

You state you are “Senior automotive writer with 28 years experience on reporting all things automotive”, then you should source your info and realize that the media only post clips of what is said during an interview. You judge me on these TV clips and therefore you are not a professional journalist.

My official view is that we, as police should be looking at anything above the 80th percentile, or below the 20th percentile and ticketing those for either going to fast or going to slow. This is my view.

I have 23 years of traffic enforcement experience, I’m a trained collision analyst/reconstructionist and have first hand experience at seeing the difference in the damage that occurs to a car at 80 km/h vs 160 km/h. If a normal car travelling at over 125 km/h crashes into an immovable object (tree/lamppost/concrete wall), you will be injured, not maybe, will be. Lets look at vehicles travelling at 70 km/h in a 60 km/h speed limit on the Lions Gate bridge, an undivided highway with only three lanes, the centre lane switching directions. If two cars at 70 km/h collide head on, it’s like hitting an immovable wall at 140 km/h, at this speed in a head on collision, people will likely die, and I have seen many people died on that bridge. On a divided highway, with proper modern concrete barriers that deflect the car, instead of stopping it immediately, higher speeds are usually survivable, light poles have shear boxes, signs are designed to break away, the road are designed for speed. The Lions Gate Bridge is not designed for speed.

I also think the keep right laws in BC need to be strengthened, too many times I see people enter Highway #1 and pull across the right lane (no cars in the right lane) directly into the left lane and remain there for no reason. Staying in the left lane unnecessarily when traffic is flowing well is dangerous and does cause collisions. However, there needs to be an exemption when traffic is heavy to allow a vehicle to remain in the left lane to increase the volume capacity of the highway during rush hour. This is common sense.

I’m a professional driver, with a class 1,6 licence, motor vehicle inspector, months of driver training on all types of vehicles, I’m a motorcycle officer with escort training, police driving instructor, pursuit intervention techniques instructor. I have been driving cars for over 34 years and motorcycles for over 38 years.

Feel free to call me, a professional police officer, any time you want to find out the real truth, don’t rely on the media or internet hacks for your information.

Chris Thompson responds:

March 5, 2015
Hi Sgt. Kravjanski, it’s Chris Thompson here, the producer of Speed Kills Your
Pocketbook. I’m sure you’re familiar with my work.

I’d like to start questioning why you seem to feel you know what’s best for road
safety. While you highlight your extensive qualifications as a police officer
and accident investigator, you convey information which is false and resort to
name-calling. In fact, you provide a first class example of why police shouldn’t
be making many decisions when it comes to speed limits.

I must admit, when my video first became so successful, I had a pang of guilt
regarding the segment where you were lasering cars on the Lions Gate. My point
of that particular segment was the unfortunately lazy editing of the news
editors in creating that story, and I thought it was possible that you were just
an honest and hard-working, if somewhat overzealous, police officer frustrated
with trying to police a law which absolutely nobody obeyed.

Now I can see that’s not the case; which is a shame, because I do agree with
your points about left-lane bandits.

You said, “What really gets to me is that [Mr. Booth passes] judgement on me without ever
speaking to me.” Booth didn’t do that; rather he said that the possibility that
the speed limit was set too low simply didn’t occur to you while you were
uniformly condemning the motoring public. He did not pass judgment on any
aspect of your personality, or take issue with your qualifications as a police
officer or accident investigator.

But I will.

You stated “My official view is that we, as police should be looking at anything
above the 80th percentile, or below the 20th percentile and ticketing those for
either going too fast or going too slow. This is my view.”

Is that so?

Traffic engineers, the Ministry of Transportation, Institute of Transportation
Engineers, numerous US DOTs, and pretty much everyone else who’s studied this
sort of thing take the view that it is the 85th percentile which should be the
guide for speed limits (with enforcement tolerances of +-10%). Notwithstanding,
while there are exceptions like playgrounds and school zones, I can think of
three possibilities of where you got the 80th and 20th percentiles from:

1. You made them up on the spot. This is unlikely, as you seem to have
thought a lot about this.

2. You mis-interpreted or mis-remembered the engineering guidelines. Also
unlikely, as the 85th percentile has been widely discussed regarding speed
limits in British Columbia.

3. You feel that the might of your individual experience outweighs the
knowledge of countless government agencies and professional engineers who have
made it their life’s work studying and planning these sorts of things.

Option 3 (you think you know better than everybody else) seems likely, and let
me explain why.

You stated that “If two cars at 70 km/h collide head on, it’s like hitting an
immovable wall at 140 km/h.” It is not, and you’re wrong by a factor of four.
Although it may seem counterintuitive for those that haven’t studied the
physics, two cars colliding head-on at 70km/h is like one car hitting a brick
wall at 70 km/h. I’ve given you the proof** below for your convenience.
By the way, Mythbusters took this on and completely dispelled your assertion

.

But the main reason I feel entitled to pass judgement on you was from when you
said, “feel free to call me, a professional police officer, any time you want to
find out the real truth, don’t rely on the media or internet hacks for your
information.”

If you’re going to call me an “internet hack” and hold yourself out as the
arbiter of the “real truth”, you’d better make sure anything you post doesn’t
include basic mistakes about the physics which you should have known from your
“23 years of traffic enforcement …[and] collision analyst/reconstructionist
experience.” If you are confused by applications of kinetic energy transfer, I
think you should stick to giving out speeding tickets – I can only assume you
have gotten quite good at that.

I am quite grateful that you commented on David Booth’s column, as it quite
clearly demonstrates the “god-complex” that some police officers have when it
comes to enforcing speed limits. And that’s the part that frightens me – you
have the power to take significant amounts of money from every-day Canadians who
simply have the misfortune to be driving anywhere in your vicinity. If more
police officers you like you spoke more often, the public would get a much
better idea of the mindset and ignorance of some of the people entrusted with
enforcing traffic.

But then what do I know, I’m just an internet hack.

Chris(chris@six7films.com)

**Proof:Numerically: Energy = ½mv^2. If one car hits a brick wall at speed v (say
70km/h), the energy dissipated in the car is 1/2mv^2. If two (identical) cars
are travelling towards each other, the energy of the two vehicles is 2 *
(1/2mv^2). The twos cancel out, and the total energy dissipated in the accident
is mv^2. Plus, there are two cars, and each car dissipates half the energy, so
the kinetic energy that each car has to absorb while crumpling is 1/2mv^2, which
is identical to the energy dissipated when one car hits a brick wall. When one
car hits a brick wall at 2v (140km/h), the energy dissipated is 1/2m(2v)^2,
which reduces to 2mv^2 (two to the power of two is four, divided by two is two),
which means there is four times the amount of energy released into a car by that
car hitting a brick wall at 140km/h than a 70km/h head on collision.

Conceptually: If you slam two identical cars into each other at identical
speeds, the physics suggests that you could draw an imaginary line in the middle
and it would look the same on each side. If that was the case, it would mean
that the car’s crumple characteristics would be identical to hitting an
immovable object (represented by the imaginary line in the middle), such as a
wall, since each car’s kinetic energy is only being absorbed by the car itself.
If you pay attention to the Mythbuster video, you can see the imaginary line.

Officer responds again:

Reply
March 30, 2015
Chris, thank you for the reply, I guess Mr. Booth needed legal representation to reply to my comments?

First, yes you are correct and I accidentally typed 80th percentile instead of 85th percentile, it should also be more like below the 55th-65th percentile for slow drivers (I never calculated that before). The formulas I wrote and used in excel have always calculated 85th percentile. I did many traffic studies over the years for certain area, all to make sure officers were being fair and not fishing.

Your Myth Buster example is incorrect; and I over simplified. It has been shown that two cars colliding at half the speed produce the same amount of energy as one car colliding at full speed. So total energy in the collision is the same, but spread across both cars. I also didn’t get into weight differential, velocity differential, metal fatigue, offset collisions and many many more factors that can increase vehicle damage during a typical head on collision. I apologize for over simplifying and you might want to dig a bit deeper into a TV show’s conclusions before using it to prove your point.

To clarify, I never called Mr. Booth any names. I voiced my concern that he was being unprofessional. That is not name calling. I would still love to talk to Mr. Booth about my thoughts on traffic safety.

I must say, although you appear to have won a legal debate several years ago as per the law firm you work for, were you a bully then too?

I was thinking for putting a jab in about lawyers making the world a safer place, but there are so many that do, so it wouldn’t be fair. Nor are you by painting all COPS as money grabbing idiots who don’t know anything about traffic safety.

I’m happy to read the new left lane laws are coming into effect, however this will leave the left lane clear for people going way too fast and above the 85th percentile.

Please drive safe and have a good and prosperous year.