Roads need to cater safely for all users
Road design should reduce the probability of accidents in advance, by means of the infrastructural design, and where accidents do occur, the process which determines the severity of these accidents should be influenced such that the possibility of serious injury is virtually eliminated. Thus, a sustainable, safe traffic system has :
- A structure that is adapted to the limitations of human capacity through proper design, and in which streets and roads have a neatly appointed function, as a result of which improper use is prevented
- Vehicles fitted with ways to simplify the driverís tasks and constructed to protect the vulnerable human being as effectively as possible; and
- A road-user who is adequately educated, informed and, where necessary, guided and restricted.
The concept can be translated into some, more practically oriented, safety principles:
- Prevent unintended use, i.e. use that is inappropriate to the function of that road
- Prevent large discrepancies in speed, direction and mass at moderate and high speeds, i.e. reduce the possibility of serious conflicts in advance
- Prevent uncertainty amongst road-users, i.e. enhance the predictability of the course of the road or street and people's Behaviour on the road.
Standards and criteria for sight distance, horizontal and vertical alignment, and associated traffic control devices are based on the following driver performance characteristics: detection and recognition time, perception-reaction time, decision and response time, time to perform brake and accelerator movements, manoeuvre time, and (if applicable) time to shift gears. However, these values have typically been based on driving performance (or surrogate driving measures) of the entire driving population. The models underlying these design standards and criteria therefore have not, as a rule, included variations to account for the special characteristics or performance deficits consistently demonstrated in research on vulnerable road users. On that purpose, specific guidelines to address the needs of for these special user categories are often proposed .