It should be noted that the number of motor vehicles registered is not the same as the number in service at any given time, but it is a reasonable ap- proximation. Registrations tend to exceed the number of vehicles in service for a number of reasons:
- Registrations are cumulative throughout the year. Vehicles registered in January may not be in service in December.
- Vehicles moved by the owner from one State to another may be registered in both States during that year.
- Vehicles scrapped during the year are not deleted from the registrations of that year.
Estimating the number of vehicles in use is becoming increasingly difficult as the States change from a fixed date beginning the registration year to some anniversary month, such as the birth month of the owner or the month of purchase of the vehicle.
Beginning with 1936, nationwide estimates of motor vehicle travel, classified by vehicle type and road system, became available for the first time. Over the 37-year period between that year and 1973, no significant increase in the use of passenger cars is indicated by the estimates of average annual travel. But when the density of automobile ownership is considered, multicar ownership is shown to have kept average travel per vehicle down, while average travel per household increased significantly. From 5.25 persons per vehicle in 1936 (0.7 passenger cars per household), the density of ownership increased to only 2.06 persons per vehicle (1.5 automobiles per household) in 1973. While fuel consumption per automobile increased by about one-third during the period, fuel consumption per household nearly tripled.
In 1973, the average annual travel of an individual truck was 11,500 miles, a small increase over 1936, when a truck averaged 10,000 miles. Single-unit trucks averaged 9,900 miles per truck per year, while the average for combinations was nearly 47,000 miles.
Between 1916 and 1973, trends in total motor fuel consumption and travel have roughly paralleled each other, and, as might be expected, both have related rather closely to the trend in motor vehicle registrations. By 1973, annual fuel consumption per vehicle had risen to only about 890 gallons from 750 in 1946 and 800 in 1966.
The upward creep of average automobile operating speed that took place between 1947 and 1972 has implications for fuel consumption and is indicative of the improvement in highways that has occurred over the years. Speed increased from 45 to 62 miles per hour on main rural highways. Stated another way, only 30 percent of the passenger cars observed in 1945 were traveling more than 50 miles an hour, but by 1972 nearly 90 percent were doing so.
Today, after almost 60 years’ experience with Federal aid to and State management of major highways, primary responsibility for about 75 percent of the Nation’s highway mileage rests with about 35,000 units of government below the level of the States (excluding the District of Columbia). But, with some notable exceptions, the roads under county and local jurisdiction, for the most part, carry relatively light traffic accounting for a small portion of the total.
In contrast, the 36,300 miles of the Interstate System open to traffic on January 1, 1975, constituting less than 1 percent of the total miles of roads and streets, are carrying about 16 percent of the nationwide total highway traffic. Adding the 6,200 miles of highway carrying the traffic where the System is incomplete, the percentage of total traffic carried by Interstate routes is 19 percent of the total carried by all highways.
The coming of the Interstate Highway System took the steam out of the toll road movement, and today most of the major toll roads carry Interstate routes over a considerable portion of their length, though Federal Interstate funds were not used to build the sections for which tolls are charged. There were 56 public toll roads in operation in 1973, with net toll mileage of a little over 4,000 miles.
Over the 57-year period between 1916 and 1973, road and street mileages in the contiguous United States increased nearly 36 percent, from approximately 3 million to a little less than 4 million. While this increase can be attributed partly to improved mileage inventories, most of it came from new construction.
Changes in rural road mileage, on the one hand, and municipal mileage, on the other, resulted from transfers of rural roads to urban, as cities grew and the Nation’s population became predominantly urban. Whereas rural road mileage increased by about 29 percent (700,000 miles), municipal mileage grew by about 80 percent (300,000 miles).
With all the participating units of government drawing as heavily as possible upon all other available sources of income, the task of developing our modern highway network would have been impossible had it not been for the ability of certain governmental units to tap a lucrative source of revenue—the motor vehicle. It is to this source of revenue, as much as to any other single factor, that the United States owes the extent and quality of its highway systems.
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