The Province of Zuid-Holland has introduced the signalised high-volume multi-lane ‘Turbo roundabout’ as a new intersection lay-out with the most important characteristic that there are physically separated driving directions, in contrast to conventional roundabouts. TNO evaluated two existing signalised turbo roundabouts with respect to traffic flow and road users’ behaviour and experience. The evaluation of road users’ behaviour and experience consisted of a road scene analysis by two human factors experts, a behavioural analysis based on video recordings and a road user survey in the direct vicinity of one of the turbo roundabouts. For each turbo roundabout, eleven hours of digital video recordings were analysed for error manoeuvres and other deviant behaviour for each approach branch. The road scene analyses indicate that, in general, at both turbo roundabouts, maximum effort is devoted to carefully indicating possible destinations before road users enter the roundabout. The route signing is uniformly and consistently designed with the same destinations on the pre-direction sign panels and on one main gantry sign panel. Roundabout arrows painted on the road surface are uniformly indicated on the gantry panel just in front of the turbo roundabout. Once one has passed the gantry sign, however, no further route directions are presented, neither on negotiating or leaving the roundabout. The video-based behavioural analyses indicate that, on average, 15 error manoeuvres/hour occurred at the turbo roundabouts. The filtering during the approach of the turbo roundabouts is conducted rather smoothly. In line with the outcome of the road scene analyses, on both roundabouts the left-turn manoeuvre appears the most problematic one. Turning left directly beyond the first traffic light was considered to be the most serious problem because one enters the roundabout against the driving direction (ghost riding). While on the roundabout, the path choice for left-turning traffic at the second traffic signal stands out most prominently. Complex error manoeuvres (several times a carriageway switching on the roundabout resulting in at least one complete round) indicate that one does not know where to go to or that one loses the right path choice completely. From the survey results it can be concluded that the interviewed road users are reasonably positive about the signalised turbo roundabout, but they indicate that habituation is very important. a lot of road users admitted that when the situation was new, they made several mistakes (wrong traffic lane choice). Many respondents also indicate that they frequently see other road users make similar mistakes. On the one hand, approaching and negotiating signalised turbo roundabouts appear to be a complicated manoeuvre, especially for the less familiar road user. We expect that recommendations for improving the lay-out and outfit of a signalised turbo roundabout (we made some) will reduce the number of error manoeuvres, but not exclude these fully. On the other hand, the traffic throughput analysis reveals a much higher capacity of a signalised turbo roundabout than of a conventional signalised intersection, but at a cost of a higher number of red runners. Based upon the results of the behavioural study and the road user survey, we recommend to be careful in applying this type of intersection, and only consider application if the traffic capacity for heavy crossing flows really requires so. (Author/publisher) This publication may be accessed by Internet users at: http://www.ictct.org/workshop.php?workshop_nr=26
Abstract