The purpose of this study was to develop a data base and interrelationships for traffic characteristics on rural, multilane highways. Primary emphasis was placed on factors influencing lane distribution. Other characteristics investigated were vehicle speeds, vehicle classifications, volumes, time distributions of flow, and noise emitted by vehicle type and weight. Most analyses were based on traffic characteristics data collected in the summer of 1973. Analyses of 1968 and 1975 traffic characteristics data were compared with 1973 data for the purpose of investigating unusual trends over the various time periods. The 1968 and 1973 surveys produced similar results; however, some changes were noted between 1973 and 1975. Much of the change was attributed to the "energy crisis" and the associated reduction in speed limit.

It was found that the addition of any variable other than hourly traffic volume, did not contribute significantly to the accuracy of predicting lane distribution of traffic. Lane distribution percentages of total traffic ranged from a 64-36 (shoulder lane - median lane) split on I 75 at the Grant County site in 1968 to a 90-10 split at the I 64 Rowan County site in 1973.

Graphical relationships and equations were developed from 1973 data which permit conversion from ADT's on rural, four-lane highways to lane distribution percentages and corresponding percentages of various vehicle types.

Average noise levels in 1973 ranged from 75.8 decibels for autos and pickups to 89.2 decibels for combination, five-axle trucks.

Average car speeds decreased by 8.3 mph (3.7 m/s) and average truck speeds decreased by 2.0 mph (0.9 m/s) between June 1973 and December 1975.

Report Date


Report Number

No. 444

Digital Object Identifier



The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Bureau of Highways. This report does not constitute a standard, specification, or regulation.