Abstract
Data from four Australian State Road Authorities are analyzed to determine relationships between mean free (spot) speeds on tangent lengths and the road factors, gradient, sight distance, pavement width and shoulder width. Such relationships are important in both road design and road safety. The analysis shows that gradient is the dominant factor influencing mean free speeds: it is probably the only significant factor as there is little evidence for any sight distance effect and no evidence of pavement width or shoulder width or shoulder width effects.