Safe Design of Rural Roads by Normalized Road Characteristics
T Richter, B Zierke, TU Berlin, DE
This Paper discusses the concept of a safe traffic system. Rural roads having self-explaining properties are designed in such way that they are in line with the expectations of the road users and that they elicit safe behaviour simply by its design.
The standard designs of rural roads vary a lot. The question which road characteristics will lead to a save driving behaviour has yet to be answered. So far various studies have conducted research on specific road design elements, but have not been able to give an answer to the questions asked here. One approach to achieve a high quality road network is the standardisation of certain road types, which are supposed to have similar road characteristics within their category, but show significant differences towards the other road types.
In the course of the development of the new guidelines for rural roads in Germany (?Richtlinien für die Anlage von Landstraßen (RAL)? the aim is to provide self-explaining and recognizable road types for motorists. According to the new RAL rural roads are being classified by traffic relevance into one of four design classes.
Within the project "safe design of rural roads by normalized road characteristics" the TU Berlin is researching which road design will affect driving behaviour and road safety positively. The project goals are to provide self-explaining and recognizable roads and therefore increase road safety by creating design classes. Based on detailed accident analysis´ the design classes were derived. The design classes consist of a suitable combination of cross-section and junction designs. Other considerations within the deliberations of safe design classes were the form of operation and the alignment.
The driving behaviour was examined in with/without and before/after situations on real roads. The empiric analysis insisted over 10,000 km tracking and fielding driving on 30 different roads. Furthermore the detected self-explaining roads were analyzed in the driving simulator of the TU Berlin. To ascertain the effect of these new kinds of roads they were compared with real roads that were implemented into the driving simulator.
Besides the driving speed, the acceleration and the lane keeping over the stretch, local measurements are made on the real road and the driving simulator. In the driving simulator the passing behaviour and the driving behaviour with oncoming traffic was analyzed additionally. Furthermore drivers? behaviour (eye movement etc.) was analyzed.
The single lane cross-section is the characteristic part of the design class 4 with not signalized junctions and a daily traffic volume of less than 3,000 cars and less than 150 trucks. The carriageway width is supposed to be 6 m.
Especially this new single lane cross-section for low volume roads showed positive results. Therefore an existing road was remarked with the new single lane marking for the first time in Germany. On these roads the average driving speed could be reduced by about 10 km/h by installing the new road markings both on real roads as well as in the driving simulator. Overall, appropriate combinations of cross-sections and junctions with the alignment in mind affect the driving speed and lane keeping positively.
The results of the project show that the driving behaviour and therefore the road safety are influenced by the road design. The results will find use in the new design guidelines in Germany.
Association for European Transport