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AOSI: Out-of-town road safety

Improvement of road safety on single-carriageway two-lane roads outside built-up areas

Improvement of road safety on single-carriageway two-lane roads outside built-up areas
In absolute numbers, the trend in road accidents has been declining for more than the last 20 years. Nevertheless, both the breakdown of the accidents as well as the residual accidents highlight the necessity of developing approaches to still further increase road traffic safety. This applies in particular to trunk and country roads. Most of the severe accidents take place on these roads, with two-thirds of all fatalities caused in road traffic accidents ensuing on these roads.

The graph shows the number of fatalities by accident type interurban Fatalities by type of accident outside urban areas (excluding motorways) in 2011

There are multiple reasons for this. As far as road design is concerned, the road network in Germany reflects the safety standards of the respective planning and construction period. As a result of this, sections of the road network exist, which no longer conform to the current state of knowledge. Their adaptation to modern road design guidelines, however, can only be implemented over a long period of time.

These reasons illustrate the necessity of developing suitable measures for the purpose of raising the road safety of particularly accident-prone sections of trunk and country roads in the short or medium-term. As the basis for developing measures and for the coordination of scientific investigations into the effectiveness of such measures as part of a large-scale test, an "Out-of-town road safety" project group (AOSI) was established by the BASt in coordination with the Federal Ministry of Transport, Building and Urban Development (German abbreviation BMVBS). This AOSI project group comprised representatives of the BASt, BMVBS, the road administration departments of the federal states and scientific institutions.

Developing measures

Potential areas for action for suitable measures were derived from a comprehensive analysis of the road traffic safety of single-carriageway two-lane roads outside built-up areas.

In accordance with the main reasons for severe accidents on roads outside built-up areas, measures were then drawn up both to enforce the maximum authorised speed and secure overtaking manoeuvres, since these represent the greatest potential for improving road traffic safety.

The photomontage shows left a stationary speed monitoring and right outside built a road with overtaking tires left: Enforcing maximum authorised speeds , right: Creating safe overtaking possibilities ((sign photomontage)

A linear configuration of stationary speed cameras (German abbreviation OGÜ) was introduced to influence the speed behaviour and thus the frequency of accidents along a longer section of road. The speed cameras were set up at an average of 2.5 kilometre intervals. The introduction of overtaking lanes (German abbreviation ÜFS) on certain road sections in conjunction with overtaking bans (German abbreviation ÜV) along the remaining two-lane intermediate sections is intended to exclude the use of the contraflow lane from a road traffic law perspective. Overtaking-lane sections between 600 and 1,200 metres in length were selected for this purpose.

Investigation methodology

On the basis of defined criteria, ten sections were selected for investigation, five to be equipped with stationary speed cameras and five for the implementation in sections of overtaking lanes in combination with overtaking bans. The investigation of the effectiveness of these measures ensued by means of a before/after comparison. Over a period of three years before and after the implementation of the measures, the accidents as well as the traffic flow and traffic speeds were recorded – the latter using double induction loops. In addition, the traffic behaviour on these sections with stationary speed cameras was also recorded via following cars. Traffic user surveys were used as the underlying data for the acceptance study.

Results

A significant improvement in traffic safety was determined not only on the sections tested with stationary speed cameras but also those with overtaking lanes (ÜFS) and overtaking bans (ÜV). This was revealed in the reduction in the accident figures, particularly in the severity of accidents.

While the speed monitoring primarily leads to a reduction in speed-related traffic accidents, the creation of safe overtaking possibilities results in significantly less major accidents caused by overtaking.

In spite of initial scepticism regarding the use of stationary speed cameras on sections tested, the evaluation of the road user surveys revealed broad approval by road users to the measures (over 90% support). These findings were influenced by the good visibility of these cameras and their clear announcement (signs) as well as – on those sections with overtaking lanes and overtaking bans – by the succession of signs informing of the distance to the next overtaking lane.

Action recommendations for the planning and design practice as well as scientific bases for the continuation of the policies regarding trunk and country roads were derived from the results of the AOSI investigation. This investigation has thus provided a valuable contribution to the improvement of traffic safety on single-carriageway two lane roads outside built-up areas.

Contact partners

Bundesanstalt für Straßenwesen (Federal Highway Research Institute)
Dr-Ing. Thomas Jährig
"Highway design, traffic flow, traffic control" section
Info
mail: info@bast.de
Technical University Dresden
"Friedrich List" Traffic Sciences Faculty
Road Traffic Installations Design Chair
Univ.-Prof. Dr.-Ing. Ch. Lippold
Univ.-Prof. Dr.-Ing. habil. G. Weise
01062 Dresden
Technische Universität Dresden, Fakultät Verkehrswissenschaften "Friedrich List", Lehrstuhl Gestaltung von Straßenverkehrsanlagen
mail: kontakt.strasse@mailbox.tu-dresden.de

www.strassenentwurf.tu-dresden.de

More detailed information