With the proper information, a skid mark will provide us with the minimum speed of a vehicle.
But why is it only the minimum?
When we are investigating a
crash, it usually involves a
vehicle hitting something. A skid
mark calculation uses the length
of the skid for a speed
determination.
51
In this example the skid is interrupted by an impact.
Clearly if there had been no impact, the vehicle would have skidded for a longer
distance. Since there was an impact, the skid distance was interrupted and shortened,
therefore, the skid calculation only gives us a portion of the speed loss. This is why it is a
MINIMUM SPEED CALCULATION.
The Virginia State Code, 46.2-880, provides a stopping distance chart that indicates
minimum speeds for certain skid lengths.
§ 46.2-880. Tables of speed and stopping distances.
All courts shall take notice of the following tables of speed and stopping distances of motor
vehicles, which shall not raise a presumption, in actions in which inquiry thereon is
pertinent to the issues:
SPEED IN AVERAGE STOPPING DISTANCES TOTAL STOPPING
Avg Driver DISTANCES:
Truck Brakes Perception- DRIVER AND
Miles Feet Automobile Brakes on Reaction Time
Per Per Brakes All Wheels (1.5 Seconds) Automobiles Trucks
Hour Second (In Feet) (In Feet) (In Feet) (In Feet) (In Feet)
10 14.7 5 6 22 27 28
15 22.0 11 14 33 44 47
20 29.3 19 25 44 63 69
25 36.7 30 40 55 85 96
30 44.0 43 57 66 109 123
35 51.3 58 78 77 135 155
40 58.7 76 102 88 164 190
45 66.0 96 129 99 195 228
50 73.3 119 159 110 229 269
55 80.7 144 192 121 265 313
60 88.0 171 229 132 303 361
65 95.3 201 268 143 344 411
70 102.7 233 311 154 387 465
75 110.0 268 357 165 433 522
80 117.3 305 406 176 481 582
85 124.7 344 459 187 531 646
Prepared by: Joe W. Atherton, ACTAR 697 - Accident Technology, Inc.