Excessive Speed?

stevieb

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I have a question in regards to skid marks and speed in an accident.
Car A comes to an intersection stop sign (cross traffic does not stop). Car A stops, looks and proceeds through intersection, now as car A nears the cross walk on the other side of the intersection (approx 100') it is hit just forward of the right rear tire by car B.
I understand Car B had the right of way because car A didnt proceed when clear. The street car B was travelling on is divided by an island of trees, each side of the street is 50 feet wide and car B's direction gave him a better advantage as far as vision.
But in this case I believe that car B is at fault for the following reasons:
1.It is a residential zone with a 25mph speed limit.

2. Car B left 48 feet of skid marks before impact, and the marks went from straight, into the direction of car A instead of in the other direction as one who was fully attentive would have tried to do to avoid contact. I believe at a distance of 48 feet when car B saw car A in its path, had he been travelling the legal speed limit, he would have had adequate stopping distance.

Is there a formula to use to determine skid mark lengths vs speed?
The reason for all this is my 16 year old son had his first accident and I am trying to help his record remain clean. I have pics of the scene to produce to the insurance co, but I would like to find a iron clad formula to determine speed from skid marks to submit also. Thanks for any comments.
 

mswaim

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The straight skid marks are not unusual, since once a wheel locks, it cannot turn in either direction, hense the straight, non-angular, locked wheel skid.

Before I would comment further, It would help to know time of day, temp., weather conditions, type of surface ie, concrete, asphalt, worn, new, oiled, clean and fresh, etc.

Lots of variables when it comes to measuring co-efficiency of friction.

It would help to know if a report was taken by local police and their findings.
 

stevieb

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There was no police report. The time of day was 5:00 pm, clear, sunny (sun to car A's back and car B's left) A was eastbound and B was northbound, old and worn asphalt (even surface, no potholes with smooth dry surface). There was 1 parked suv at corner blocking r/h view from car A @ stopsign, and nothing blocking view of car B from his direction. Hope this helps.
 

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The length of the skid is porportional to the square of the speed. Assuming the vehicle would stop in those conditions in 140' from 60MPH, if it were going 30MPH it would be able to come to a complete stop in about 35'. This of course assumes that the vehicles brakes are in decent condition and that they are adjusted properly and that the vehicle was not overloaded. A large SUV for example, typically stops in 160 or so feet from 60MPH which means that at 30 MPH it would stop in 40'.
Even shorter for speeds of 25 MPH. A skid of 48' (did you measure it exactly) would suggest something wrong with that vehicle's brakes or a speed of much greater than 25 MPH. Granted I'm not an accident reconstruction expert, but I am an engineer and know a bit about physics and vehicles.

Good luck! You may be able to show in court that the other vehicle was speeding, I don't know if that would entirely exonerate your son.
 

mswaim

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Most insurance companies have calculator software that they use in the absence of a police report when their investigators give the facts a "once over".

Using your numbers, it looks like vehicle B was traveling either 31-32 mph on the low side, or 33-35 mph on the high side of the equation, the middle-ground will most likely be where they settle ie, 33 mph.

The CA basic speed law 22350 CVC states that no one shall operate a vehicle at a speed too great for existing conditions.

The code also contains sections 22106 and 22107 that state that no vehicle stopped or parked upon a highway shall move forward or backward in a manner that is unsafe or places others in harms way.

Considering there were no injuries (that is an assumption) and no witnesses (also an assumption) the two insurance companies will most likely assign blame proportionately.


This is a new craze in California, especially where both drivers actually have insurance!

Good luck. :beer:
 

stevieb

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Thanks for all your help. I was suspect of the speed being too great. By the way, car B was a 2000 Mitsubishi Mirage with four occupants and car A was a Pontiac Montana. What convolutes this incident is the Montana was his friends whose owner doesnt want to even notify his ins co (we all know the insurance goes with the car).
I talked with car B's insurance co and told her of the skid length and she was not aware of that and agreed there may be a shared responsability. I am just worried that car B's insurance Co. may not be as favorable to my sons side, even with all the evidence. But I am convinced that 48' (yes I measured it and took pics that will be submitted) is excessive speed and this was the leading factor in the accident.
I haved worked for a public transit agency for 20 years and have performed a lot of post accident mechanical inspections and braking efficiency testing. I dont remember the CVC section but a 40' bus must be able come to a stop in no more than 40' at 20 mph. In all my years I have never had one stop in more than 24'. So if a 35,000 lb. bus can do that a car shouldnt have any problem. Again, thanks for all your help.
 

jshen

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See Link

Try this link:

Skid mark analysis doesn't always get an answer. For example, what effect ABS brakes has on vehicles. Accident reconstruction appears to be heading and relying on the the car's computer in either the ABS unit or air bag unit. Check the part about "crash data recorders...... Very interesting link.


http://www.harristechnical.com/skid33.htm

:read:
 
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