Transportation and Vehicle Safety: tire skid marks, mail client, tire markings

Question
My friend and I were in a car accident. We pulled into the passing lane (45mph speed limit)Upon getting in the lane we saw a car no breaking lights or turn signal barely moving, my friend slammed on breaks but we hit the car anyway. No-one was injured,but my friend and I were checked at the hospital. While there an officer interviewed us. He asked my friend how fast he was going, my friend said speedometer read 48mph. Officer said, "Skid marks don't lie there was 153 feet of skid which is excessive speed. Both my friend and I know we were not going excessively fast and that we did not slide that long of a distance. After we left the hospital we went back to the scene which was 1/2 mile away.and measured the skid marks. They were only 70 feet. We realize there are lot of differential on speed marks but man this guy was way off. Anyhow our question to you is with everything we've read on tire skid marks, the skid starts light and ends dark where the vehicle stops or where impact is, how come ours is the opposite. ( there are no other tire markings on the road.) What gives?

Answer
Hello Mary Ann, and welcome to AllExperts.

I'm sorry this has taken so long, but for some odd reason, my e-mail client had not received it. Thanks to AE for the reminder!

Anyway, to your issue.....

Your observations are good Mary Ann !!

As you know, the darker color of the skid marks indicate the greater pressure that was placed on the break pedal, and therefore greater weight and load was placed on the tires. This caused more of the tires rubber to be scrubbed off and imbedded Into the asphalt.

Panic breaking (full-on emergency braking) normally leaves an immediate darker residue on the pavement, and can continue that way till impact, or lighten as the break pedal pressure is reduced or released, normally due to the emergency having passed.

The reverse pattern suggests that the amount of initial braking (heavy) was considered sufficient for the event, and during the braking event, something changed requiring greater effort to stop the car that escalated to panic braking. An example would be someone braking heavily in front of you, and you apply enough braking to remain a safe distance from them. However, they have now gone from heavy to panic braking, requiring you to follow suit.

Keep in mind also that as you respond to someone braking in front of you, there is a lag time. It takes 3/4 of a second to perceive a problem and another 3/4 of a second for you to decide what to do and begin that action. Then means that 1-1/2 seconds will go by before actual braking begins. At 45 mph, you are traveling 67.5 feet per second. Depending on the amount of distance you have between your car and the one in front, a difficult situation can easily turn into an imminent collision.

In this suggestive scenario, time tends to slow down, and what initially seemed appropriate and sufficient braking becomes insufficient, requiring greater braking effort.

As to the differences regarding what the officer had given and your observations of the skid marks in question, I cannot answer that. There are too many factors, variables and guess-work involved to even give a reasonable opinion.

While I believe you were looking for something more useful, this is the best I can offer given the facts at hand. I hope this works for you.

I do hope you get this resolved. Best of luck Mary Ann !!

Terry