Roundabouts and tramways: study on the influence of certain design criteria on tram - road vehicle accidents

Published on 09/10/2023

Initially published in 2008, the "Roundabouts and tramways" guide was first updated in mid-2017 to take into account comments from the industry following use of the guide and to update experience from roundabouts in service.

Several configurations were nevertheless identified to be in need of in-depth analysis to ensure that the differences in accidentology observed did not undermine certain recommendations.

At the end of 2017, STRMTG therefore tasked Cerema with conducting a study to provide a more detailed analysis of the influence on accidentology of the various criteria defined in the guide for the following configurations:

roundabouts with at least one leg (entrance and/or exit) crossed by a tramway platform (phase 1);
medium-sized roundabouts crossed by tramway tracks (phase 2);
large-radius roundabouts crossed by tramway tracks (phase 3).

The study analysed data on collisions between trams and motorised road vehicles (excluding bicycles) between 01/01/10 and 31/12/19. The influence of road traffic levels was not analysed due to a lack of data.

Overall, the study confirmed the relevance of the existing recommendations set out in the guide.

For tramway track crossings located on a leg of the roundabout, at the entrance and/or exit, it backed up the idea that a minimum distance from the roundabout must be maintained, although this distance has been increased from 15 m to 20 m.

For roundabouts crossed by tramway tracks, an external radius of 16 m was also confirmed as the threshold value above which collision rates tend to increase.

Angers, line A, Ave. Pierre Mendès France (Google Earth)

Three design criteria were also highlighted as having a particularly positive influence on accident rates: a circulatory roadway width of 6 m or less, a high level of contrast between the tramway tracks or its limits and the surrounding roadways, and preservation of a single lane entering the roundabout.

The rest of the results did not make it possible to draw any further conclusions regarding the influence on accidentology of compliance with the other recommendations in the guide, but neither did they undermine them.

The results of the study will be integrated into a consolidated version of the “Roundabouts and Tramways” guide to be published in 2023-2024. This update will also offer an opportunity to integrate the erratum published in May 2018 and to take into account other tramway standards published since 2017.

Since 2019, the report on tramway - road vehicle accidentology in roundabouts published annually by STRMTG in the "Annual report on the tramway fleet, traffic and operating events (in French )" has already been updated to incorporate the initial findings of this study. In particular, a more detailed analysis of the “14-22m” category is included.

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