there were 2,859 fatal accidents on this rural mileage. These accidents took 3,460 lives.
ACCIDENT RATES
The average rate of fatal accident occurrence on rural sections of the designated interstate highway system was 9.04 per hundred million vehicle-miles. This may be compared with an approximate rate of 9.11 fatal accidents reported for all rural highways in the United States in 1947. However, the accidents on the rural interstate system resulted in fatalities at the rate of 10.94 per hundred million vehicle-miles, whereas the corresponding rate for all rural roads, at 10.66, was slightly lower.
It is apparent that the rural interstate system, in its present state of improvement, is about as safe as, but certainly no safer than, the average of all rural roads, and since its traffic is far above the average in volume, it accounts for an exceptionally large proportion of the annual highway death toll.
RELATION OF ACCIDENT RATES TO LANE WIDTH
On the system as it is presently improved, the fatal accident rate for all two-lane sections was 9.19 per hundred million vehicle-miles. On all three-lane sections, the corresponding rate was 9.08; on undivided four-lane sections, it was 9.41; and on all divided multiple-lane sections, it was 7.65. The superiority of the divided sections from the standpoint of safety is rather marked; the apparently anomalous rate for the three-lane sections possibly results from the fact that these sections carry traffic which in relation to their width is somewhat lower than the similar relation on the existing two-lane roads.
Even the more gratifying rate shown for the existing divided highways is not as low as it might have been had many of these sections been more adequately designed in respect to elements other than their width.
REDUCTION OF ACCIDENTS THROUGH IMPROVEMENT
What a really adequate improvement of the entire system would do to reduce the fatality toll as it stands at present is, of course, a matter of speculation. Some measure of the possibility may be gained from the lower accident rate recorded for portions of the system deemed adequate in their present condition. Of 1,900 miles of the rural system on which this report indicates that no improvement is required, the rate of fatal accidents, known for 1,689 miles, was only 5.65 per hundred million vehicle-miles. Had all parts of the system—its two-, three-, and four-lane sections, divided and undivided—had an accident experience as low in rate as these 1,689 miles requiring no improvement, the fatal accident rate for the whole rural system would have been 5.35 per hundred million vehicle-miles, a reduction of 40.8 percent from the actual rate of 9.04.
At the lower rate there would have been 1,167 fewer accidents and more than 1,400 lives would have been saved in 1 year on the rural sections of the system only.
Appraisal of Current Conditions and Deficiencies
The condition of the existing roads constituting the system having been determined in detail by the several State highway departments,
