Volume 1: Cross-section widths of one-lane roads outside built-up areas and traffic safety: In order to check the traffic safety of various cross-section widths on two-lane roads outside built-up areas, a collective of sections for investigation comprising the b2, c2, d2 and e2 cross-section types was elaborated based on reference to previous investigations and consultations with the competent road construction companies.91 of these sections were in the old Laender and 24 in the new Laender. The total length of all sections was approximately 760 km. The sections in the old and new Laender were observed separately. Accident data were available on some of the sections for the period 1988-1990. For the period up until 1995 the data had to be recorded and supplemented at the police departments. A total of 6,600 accidents were available for evaluation. They formed the basis for calculating the accident variables (accident rate, adjusted accident rate, adjusted average accident rate). The distribution of the accidents according to cross-section types and various characteristics, such as accident type, kind of accident or cause of accident, produced differences both between the individual cross-section types and between the old and new Laender. The accident variables of the sections in the old Laender were more favourable in the case of the c2 cross-section than in the case of the wider b2 cross-section. Accident severity, in particular, was much greater on b2 sections. In the new Laender the results varied due to the small section collective and the problematic data situation caused by the rapidly changing accident occurrence in comparison with the old Laender. In the new Laender the b2 and d2 cross-sections had more favourable values than the c2 cross-section. The original report contains a large number of appendices inter alia on accident parameters of the various test roadway sections, accident causes, kinds of accident, types of accident and accident cost rates. These appendices were omitted in the present publication. They can, however, be consulted at the Federal Highway Research Institute. References to these appendices were retained in the report. Volume 2: Special investigation into cross-section type b2+1: In addition to the cross-section types already considered, roads with b2+1 cross-sections were to be included in the investigation. For this reason, accident data on 14 sections with b2+1 cross-sections were recorded and evaluated. A total of 489 personal injury accidents and accidents with major material damage were recorded. 393 of these were accident types not involving turning off, into or crossing roads (accident types 1 and 4-7); these were relevant to the investigation. Accidents while overtaking occurred slightly more often on the three-lane roads than on the b2 sections. With regard to the kind of accident, approx. 30% of the accidents came under “leaving the carriageway to the left or right" and approx. 20% under “collision with an on-coming vehicle". Both kinds of accident therefore occur more frequently on b2+1 sections than on b2 cross-section. The accident rate, accident cost rate and the average accident costs are lower on b2+1 cross-sections than on b2 cross-sections, with regard both to the accidents not involving turning off, into or crossing roads and to accidents as a whole. The accident cost rates are particularly low compared with the b2 sections. Although accidents with severe personal injury occur less often on the b2+1 cross sections, they are normally more severe. This corresponds with the tendency for the costs per accident to be higher on well designed high performance roads with high vehicle speeds. The accident rate was not dependent on the traffic volume. When comparing the accident variables of traffic volumes typical for b2+1 cross-sections (DTV > 12,500 vehicles/24h), the safety level was seen to be clearly higher on the three-lane type. (Author/publisher)
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