Opinion ID: 1788754
Heading Depth: 1
Heading Rank: 9

Heading: Characteristics

Text: On a hard pavement, a few feet of an acceleration scuff looks just like a braking skidmark (M in Exhibit 65). On soft, or loose material, however, you can see a difference. The spinning wheel kicks loose material backwards out of the furrow. The beginning and end of an acceleration scuff are quite distinctive. If the vehicle is stopped on paving to begin with, the tire spins in one place for a moment before the vehicle begins to move on. That spot becomes very hot and leaves a very dark mark on the road surface. Sometimes, on bituminous concrete paving, the bitumen melts and the spinning tire digs out an actual depression in the surface (S in Exhibit 65). But if the vehicle is moving when the wheel begins to spin, no special starting spot is made. The end of the acceleration scuff gradually fades out as the vehicle reaches a speed at which the tire is no longer slipping on the road surface (E in Exhibit 65). Often, as the car accelerates, weight shifts to the rear (as contrasted to the front in braking), tires are overloaded, overdeflect, and leave edge marks. Thus, a section of such a mark would look much like a braking skidmark or perhaps a flat-tire mark. Two-wheel acceleration scuffs occur when the vehicle has a limited slip (Positrack) differential that prevents a single wheel from spinning. Sometimes cars without such differentials leave two marks for a short distance when accelerating very rapidly. Roadway artwork is produced, usually by smartaleck drivers, who back up and then shift gears to start forward before they have stopped going backward. That leaves a hook in the scuffmark where the car stopped going back and started going forward. The spinning wheel has lost traction and if both wheels spin, the vehicle can easily slip downhill on a cross slope. Sometimes these loops are repeated to leave an elegant pattern on the road such as shown in Exhibit 66. By this means, the driver tries to impress on-lookers or passengers in the vehicle. Studded tires are intended to give improved traction on slippery surfaces. On a spinning wheel, they can dig into ice and snow to get a better grip on the road. If, while the wheel is spinning, studs strike the pavement, they may leave a special form of scratching which has a braided appearance (Exhibit 67). This is not clearly visible while the road is wet or snow-covered, but it is easily seen when the road dries. If a wheel spins for several revolutions on one spot, marks left by studded tires show less clearly the mark of each stud. Studded-tire skidmarks look different; they are straight parallel scratches without the braiding effect (Exhibit 9).