Current speed limits are not adequate in some zones. In some areas, the limit should be understandable and acceptable for drivers, thus making it more respected by drivers than at present. The envisaged scheme consists of a basic limit, according to the highway type. This basic limit can be raised or lowered depending on the design features of the section and the specific and variable circumstances of environment and traffic.
The main aim of the REVEL research project was to achieve a method for setting an adequate speed limit for each road section, by providing a model for use by road managers.
Tasks done in REVEL project were:
- The measurement of real circulation speed in a set of test sections, both for data coming for counting loops and from data coming from on-board GPS equipment. The relation among these data, density, track characteristics and other environmental features (night, rain, etc) has been studied;
- The evaluation of traffic accident rate of the test sections in the measurement conditions, trying to establish a security profile. Particularly, a detailed analysis of the circumstances of the accidents with victims which has "too much speed" as a reason has been done;
- The development of the security criteria for each kind of road and a system to evaluate given safety levels. Particularly, simulations of effects of traffic congestion and circulation speed on traffic accident rate have been done;
- The use of safety criteria developed to establish several advices about an adequate speed limit for each test section;
- The evaluation of the new speed limits depending on their applicability, their acceptability and the safety benefits obtained, both for the management administration and for the whole.
The project was deployed by the following activities:
- state of the art;
- design of experimental phase;
- measurement of speed profiles;
- development of security profiles;
- model of speed limits;
- specific criteria for speed;
- basic limit of the speed for each road type;
- speed limit adequate for each test section.
In order to achieve the set objective, theoretical studies and data analysis have been carried out. Data included real accidents and speeds, and many of them came from pilot sections selected for this purpose.
Based on actual speed measures obtained from different selected road sections, a new methodology for modelling a speed profile has been derived. This model should represent both space and time speed distribution.
In addition, a new method for modelling a safety profile from speed measures has been developed. This profile has been related to the specific design features of road sections (with its inherent own risk factors) which resulted in its own accident record.
Once the modelling was accomplished, both the safety profile and the speed profile have been compared in order to find if there was any kind of relationship between them.
Starting from the risk evaluation results, a set of specific safety criteria has been obtained for each road type.
Road managers therefore have at their disposal a tool for setting speed limits in a rational way which can be for drivers, and for relating them to the design speed.
The use of passive search GPS equipment in the operative speed profile sampling. Several experiments have been designed using GPS data in several locations and the data obtained processed. These data allowed the average track (through the edge of the road in each lane) to be obtained.
The characteristics of the road sections selected to develop the experimentation were: closed sections (without intermediate connections), with an average length between 5 and 10 km (to ensure free flow), communication between extremes.
This experimental study was based on the geometry of the road and the speed profiles observed in order to model the speed profiles of operation. Other factors like: road transversal section, visibility, desired speed, etc, were taken into account.
The results obtained allowed a geometric restitution of the trace made by the vehicles in each sense. Also, they allowed the road geometry to be obtained and the improvement of the observed speed profiles.
The policy implications of this project are related to the assessment of authorities for the application of speed limits depending on the characteristics of the road.