THIS FIGURE SHOWS A STEADY INCREASE IN THE AVERAGE SPEED OF FREE-MOVING VEHICLES ON RURAL INTERSTATE
HIGHWAYS AND IN THE PERCENTAGE OF FREE-MOVING VEHICLES EXCEEDING 55, 60, AND 65 MPH UNTIL THE MIDDLE OF
1973. THE SUDDEN DECLINE IN 1973 CAN BE ATTRIBUTED TO THE FUEL EMBARGO WHICH BEGAN IN SEPTEMBER OF
THAT YEAR AND THE ENSUING IMPOSITION OF A NATIONWIDE 55-MPH SPEED LIMIT. THERE IS A SLOW INCREASE
IN THE TREND AFTER 1975.

α

Fig. 1.32 Speed Trends on Rural Interstate Highways' "All data represent free-moving traffic on level, straight, noncongested sections of rural interstate highways. Data shown between 1960 and 1975 represent speed trend information collected by several state highway agencies (normally during the summer months) and submitted in annual speed trend reports. Since October 1975 all states have monitored speeds on several highway systems, including the interstate system, as part of the 55 mph speed limit monitoring program. The data are reported to FHWA on a quarterly basis.

Source: U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 1976, Washington, D.C.. p. 33.

MILES PER HOUR

PERCENT

Fig. 1.33

α

Large and Medium Air Traffic Hubs in the United States, 1976.

"Air traffic hubs are defined in terms of the percentage of total U.S. passenger enplanements at the hub.

Source:

Civil Aeronautics Board and U.S. Department of Transportation, Federal Aviation Administration, Airport Activity Statistics of Certificated Route Air Carriers, Washington, D.C., December 31, 1976.

Source: U.S. Department of Transportation, Federal Aviation Administration, Current Aviation Statistics Air Traffic Activity Fiscal Year 1976, Washington, D.C., November 1976, p. 2.