Speed regulations and speed limits are intended to supplement motorists' judgement in determining speeds that are reasonable and proper for particular weather and road conditions. Limits are imposed to assist enforcement personnel and to promote better traffic flow by reducing the wide variance in speeds. Virginia's General Assembly has granted authority to the Commonwealth Transportation Commissioner, who heads the Virginia Department of Transportation, and to cities and certain counties and towns to establish speed limits not exceeding the maximum allowed by law for highways under their jurisdictions. The General Assembly retains authority for establishing statewide maximum limits. The engineering investigation involves a study of the geometric design of the road.
Engineers review such items as lane width, pavement type and condition and terrain.
In addition, the engineers look at parking conditions, commercial and residential development along the road and the number, width and types of entrances and intersecting streets. The traffic investigation involves gathering and analyzing traffic-related data. Engineers study the prevailing vehicle speeds, average test runs, traffic volumes, accident experience and traffic control devices that affect or are affected by vehicle speeds. Federal legislation enacted in 1995 gave the individual states the authority to establish their own maximum speed limits. Prior to the 1995 law, federal law required that the maximum speed limits on interstate highways be 65 mph for rural interstates and 55 mph for urban interstates.