Speed limits have been established for the good of the motoring public, primarily for purposes of safety. A study has shown that by reducing the number of violators on freeways, the resulting more uniform speeds contribute to improved capacity and safety (22). The effectiveness of a speed limit on a facility depends on the degree of enforcement and public support (3,4). The public will support and obey speed limits that are safe and reasonable; however, speed limits that are illogically restrictive cannot be enforced except by tremendous effort and expense, and then usually not for 1 ong (3). It is the duty of traffic engineers to establish speed limits by careful investigation and evaluation. The most commonly used method of establishing speed limits is to take the 85th percentile of the observed speeds (32,26). J. C. Oppenlander suggests another method of establishing the best operating speed by optimizing the three resources expended in highway transportation: the economics of vehicle operation, the value of time, and the safety of travel (33). Driver Characteristics The speed a driver chooses is dependent upon his desires and environment; therefore, speed control is difficult because of variations in the driving behavior of individuals (3,22).

The results indicate an increase of 0.9 mph in the average speed of all passenger cars and an increase of 2,2 mph for heavy trucks to that of the 1974 study.

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This report is the annual continuing study of speeds of vehicles on runl Indiana lIighways. Observations of spot speeds were taken on Interstate, four-lane, and twolane high ... ays throughout the state during the~onths of June, July and August 1972. Analysis of the speeds sho...ed the overall average speed for passenger Cars "'as 65.20 ..iles per hour. The overall aver.ge speed for heavy trucks .... s 57.56 miles per hour. This was 0.33 mph mOTe for passenger cars and 0.79 mph more for trucks than sillilar data given for 1971 at the $3l1e locations (except for station 10 ... hich had been shifted 0.8 111le north...ard). Sillple linear repression analysis sho...s an overall 0.75 .. ph increase of speed for all classification of vehicles and high... ays over the last 11 years. This trend is a bit less than that of a ten year period cnding five or six years ago and appears to result frolll a "leveling-off" of lIlaximulll speeds in recent years. (See Figure A) Interstlte Highways '-' lIiles south of Junction " " LO .ile west 0' Junction " '" LO mile east 0' Junction 0' Post Road ,"S miles north of Junction of SR 16. Four Lane High~ays '-' .,ites south of Junction of SR " L. mile east of Junction of " " LO mile north of South Junction 0' " , LO mile~est 0< Klondike "0 Lane IliShwlYS LS ,.ites east of Junction 0' 1-69 '-' .. ites south 0' Chalmers