Vehicle deceleration in beds of loose gravel: Tests are described in which a vehicle was driven into beds of gravel of different depths and types, at entry speeds of between 10 mile/h and 60 mile/h. The tests showed that small stones graded 3/8 to 1/4 in decelerate a car somewhat better than large stones graded 1 1/2 to 3/4 in, and that rounded gravel is a little more deficient than angular gravel. However, angular gravel is generally available at about half the cost of rounded gravel, and 3/8 to 1/4 in angular gravel to a dept. of 12 in provides a good compromise between effiency and cost. The deceleration rate for this gravel bed was 0.45g for unframed runs at about 40 mile/h, the stopping distance in the latter case being 55 ft. The mean deceleration rate of the test vehicle braked on a good road SURFACE WAS o.6g. from 40 mile/h. It is concluded that gravel beds might be used at sites where conventional guard rails, if erected, would be struck at angles approaching 99.
Samenvatting