- Current speed limit policies
- Education and publicity campaigns
- Information about the speed limit in force
- Road engineering
- Speed enforcement
- Traffic conditions
Speed limits are at the core of any speed management policy. Speed limits should reinforce drivers' assessment of the safe speed to travel along a road and be complied with by most drivers. Current speed limit policies differ between countries. A speed limit must reflect the function and quality of the road to ensure a safe speed limit. In addition, a speed limit will be supported by (changes in) the characteristics of the road and the road environment in order to be credible for the road user.
X-LIMITS approach used in Australia and United States
The computer program X-LIMITS originally developed by ARRB for use by Australian and New Zealand state road authorities has been further developed as "USlimits" in collaboration with FHWA for application in the United States. The program requires data to be input on density of development, frequency of access, road function, carriageway characteristics (such as number of lanes and carriageway separation), flow, interchange spacing, existing vehicle speeds, adjoining limits, and any special features such as high local crash rates. On the basis of this data, the program calculates a recommended speed limit.