NCJ Number
63356
Date Published
1975
Length
19 pages
Annotation
THIS TRAINING UNIT IS DESIGNED TO PROVIDE THE STUDENT WITH EXPERTISE IN ESTIMATING VEHICULAR SPEED FROM PHYSICAL EVIDENCE AT THE COLLISION SCENE.
Abstract
OBJECTIVES OF THE TRAINING UNIT INCLUDE IDENTIFICATION OF FACTORS RELATED TO ESTIMATING VEHICULAR SPEED SUCH AS VEHICULAR DAMAGE AND SKIDMARKS. SKIDMARKS CAN YIELD SUCH INFORMATION BY CALCULATION/DETERMINATION OF DRAG FACTOR, CALCULATION OF PERCENT OF GRADE, AND DETERMINATING SPEED BY MEANS OF CALCULATION AND USE OF THE 'SPEED NOMOGRAPH.' THE LENGTH OF SKIDMARKS NEVER INDICATES ALL OF THE VEHICULAR SPEED PRIOR TO THE COLLISION. THE VEHICLE IS ALWAYS GOING FASTER THAN THE SPEED INDICATED BY THE SKIDMARK; IT CAN LOSE SPEED IN ONE OR MORE OF THE FOLLOWING WAYS BEFORE STOPPING; (1) BRAKING WITHOUT SKIDDING; E.G., BEFORE THE SKID BEGINS, DURING GAPS IN SKIDMARKS, AND AFTER SKIDMARKS END; (2) SKIDDING WITH ONE OR MORE WHEELS BEFORE A SKID BECOMES APPARENT; (3) STRIKING OBJECTS ENROUTE TO THE SKID OR COLLISION; (4) STRIKING AN OBJECT IN THE FINAL COLLISION; AND (5) VAULTING OR ROLLING. WHEN A SKID TERMINATES IN A COLLISION, THE SPEED LOST DURING THE SKID MUST BE COMBINED WITH THE SPEED LOST DURING THE COLLISION TO ESTIMATE THE SPEED BEFORE THE SKID BEGAN. ALSO EXPLAINED ARE HOW TO OBTAIN THE LENGTH OF THE ACCIDENT SKID USING FIELD MEASUREMENTS; HOW TO DETERMINE THE DRAG FACTOR FOR SKIDDING TIRES; HOW TO DETERMINE THE SKID RESISTANCE FOR SKIDDING TIRES; AND HOW TO DETERMINE THE MINIMUM SPEED FOR THE ACCIDENT SKIDMARK. FORMULAS, THE SPEED NOMOGRAPH, AND A TABLE ARE INCLUDED, AS WELL AS A QUIZ. (PRG)