There exist small tendencies which point in the direction of enhanced traffic safety problems with the introduction of extra-long trucks. The purpose of a recent VTI study has been to investigate if the introduction of extra-long and heavy vehicles has an effect on traffic safety on Swedish roads, especially in relation to overtaking. In the study, traffic safety effects have been measured in terms of road user behavior concerning speed and accelerations and time slots. Road user experiences and heavy truck drivers’ experiences have also been studied. The traffic conflict technique presents how time-to-collision and speed are related to accidents and near accidents. The traffic conflict technique has been used as a starting point for the discussion on how the introduction of extra-long trucks might affect traffic safety. The report presents four empirical studies: a focus group interview study with heavy truck drivers, an interview study with drivers of extralong trucks, a simulator study and a field study. The simulator study and the field study focus on overtaking. The purpose with the focus group interview is to investigate if the heavy truck drivers (that do not drive the extra-long trucks) have an opinion on how extra-long vehicles might have an impact on traffic safety. The purpose with the interviews of drivers of extra-long trucks is to grasp the experiences they have of the extra-long trucks. Truck drivers that do not drive extra-long trucks believe that the introduction of extra-long trucks will create a number of traffic safety problems especially in terms of conflicts with ordinary road users. The drivers of extra-long trucks do not experience the problems that ordinary truck drivers predict. The problems they experience can be taken care of with more planning (thinking ahead). They also believe that the traffic sign on the back of the extra-long vehicle has a positive effect. The truck company, working environment and truck equipment are other important aspects mentioned by the drivers of the extra-long vehicles. The simulator study investigates overtaking situations on a 2+1-road, with extra-long trucks (30 m) and an ordinary truck (18.75 m). The results reveal that the distance from the back of the truck to the point where only one lane exists affects car drivers’ decision to overtake, independently of truck length. If the back of the truck is in the same position, the time slot for a safe overtaking was reduced significantly for extra-long trucks compared to ordinary trucks. Overtaking speed was, however, the same (approxi¬mately 117 km/h). The field study also studies overtaking situations with an extra-long vehicle (30 m) (with a license to drive on a specific road) and a reference vehicle (24 m), on a 2+1 road and an ordinary 2 lane road. Overtaking vehicles were video recorded with the purpose to measure overtaking behaviour but also in order to be able to contact the road users by telephone. The overtaking personal car drivers did not experience a traffic safety conflict on the road at hand. They did not even remember overtaking an extra-long vehicle. The number of data points was relatively few, especially for the reference vehicle. No significant differences were obtained for overtaking speed or time slots. The overtaking speed was, however, relatively high for both trucks. On the other hand video analyses revealed a small overrepresentation of critical time slots for critical overtakings of the extra-long truck on a normal road, but not for the 2+1 road. The conclusion is that there exist small tendencies which point in the direction of enhanced traffic safety problems with the introduction of extra-long trucks. The results should, however, not be overinterpreted since the number of data point was few and collected in specific situations and in specific conditions. A conclusion is also that more research is needed. Not to be forgotten is the reduction of the number of trucks on the road if extra-long trucks will be permitted. (Author/publisher) This report may be accessed by Internet users at http://www.vti.se/en/publications/traffic-safety-effects-when-overtakin…
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