Detecting And Recording Skid Marks

thank you [Music] Sarge you have a minute sure Jerry have a little trouble not exactly I'm just finishing up the report on that accident by Roosevelt School where The Pedestrian got hit oh yeah that's your first Batman wasn't it how you making out okay I guess that's what I wanted to talk to you about to see the car lay down some skid marks and I thought I'd take you up on your offer to check me see if I missed anything I think we can make a case on this one sure enjoy be glad to gave this one a full treatment didn't you these photographs you took at the scene that's right that one shows us skid marks you can see they lead directly to the wheels of the car that's a good start positive identification of the car with the skid marks is one of the requirements mentioned in the manual by the way did you get a witness who saw the car lay down these marks no but I got a witness who saw the car sitting on the end of them after he heard the Screech good enough did you establish the beginning of the skid or each of the four wheels started breaking yes sir that's one lesson I learned well first I viewed the pavement from a low position looking down the skid marks toward the car I had Sam I was working with Sam Freeman that day I had Sam kneel down at the beginning of the skit we found the positive part of the skid mark and then I could faintly see the shadow where the right front wheel started to slide before it got hot enough to smear Sam ran his finger along the shadow mark at the beginning of the Shadow I had him stop and make a mark using a yellow crayon like you said in class did you repeat this little act for each of the four wheels yes we did and each time Sam not only marked with a breaking began but he wrote on the pavement the wheel which made each one you know whether the shadow was made by the front left or the rear right after we got all finished locating these Shadows we snapped a few pictures then we measured the skid marks Now Jerry how do you tell the difference between a front and a rear tire from the skid I'm not sure but I suppose the front tires grabbed first no there's a more positive way than that when the brakes of an automobile are applied the weight shifts onto the front wheels because of this increased weight the trends of the front tires Arch so that only the shoulders of the tread ride hard on the pavement you get two narrow parallel marks from each tire instead of one wide smudge you'll learn something every day by the way Sarge I look for that polishing and erasing action you talked about and I couldn't find any maybe there was a reason what kind of pavement did you have asphalty concrete that explains it you don't get a polishing or erasing action unless you have dirty concrete did you check for burnt off rubber along the pavement yes we did at the beginning of the skid the rubber was like dust but further along it was as if the rubber was melted off the tire it was a sliding Tire gets that hot there were no interruptions in the skid mark indicating that the braking was continuous the full stopping distance obviously the driver didn't pump his brakes did you measure and record the skid marks yes we did they're all on this field sketch now this is the probable path of The Pedestrian prior to getting hit why didn't you show the root of The Pedestrian pedestrians don't leave skid marks and you said not to put anything on the field sketch I couldn't see myself a field sketch can be used as evidence sketch looks okay to me I see you recorded the location of the skid marks by showing measurements from the curb line it's good I also remember to check the weather and Road surface conditions the pavement was dry and there wasn't any gravel or leaves or anything like that I know these things can influence the normal gripping effect of a skidding Tire I also checked to see if there was any greater slope this gave me a chance to use that little template well anyway the road was almost perfectly level did you make a test kid using the same car at the same place under the same conditions like it says in the manual sure did two of them the car was drivable and the driver had gotten over the shake so we let him do the driving I rode with him and when we were doing 25 the speed limit I told him to hit the brakes hard and to hold them to a full stop he did we laid down some beautiful Burns almost at the exact spot Sam and I measured the new marks and compared them with the original marks there was quite a difference good enough did the tests satisfy the driver that skid marks mean something yes it did especially when I called to his attention that the test skid with his car at the same location at 25 miles per hour the speed limit was approximately half the length of the skid he laid down in an effort to avoid the pedestrians you call this to his attention I sure did what'd he say well the first thing he said was I'm a son of a gun only he didn't say gun from the way he talked I'd say he'll probably plead guilty especially if the pedestrian makes the grade you should if I'm a judge of skid marks I'd say the man was driving at least 40 miles an hour possibly 45 and that's much too fast for that location well that's what I figured and that's why I did everything the book says well Jerry you did a good job you gathered sufficient information to permit calculation of speed by a qualified person to be certain he's gathered all the evidence an officer should have a regular investigation routine a sort of a metal checkoff list which might include locate skid marks protect them from obliteration by passing vehicles link the skid marks to the vehicle measure and photograph the skid marks make a field sketch locate the skid marks with fixed objects nodes influencing conditions such as gravel leaves moisture ice or snow on the pavement and whether there's any grade note the condition of Car and Driver record all information carefully whenever possible make a test skin with that kind of a systematic accident investigation routine an officer will be able to prepare a clear and complete report like a fingerprint at the scene of a crime a skid Market scene of an accident is most important it is necessary therefore to detect and record skid marks carefully foreign [Music]