The aim of the present study was to elucidate car drivers' spontaneous reaction to MCS (Motorway Control System) signalling. The study was carried out in the VTI Driving Simulator on motorway sections with three lanes in each direction. It included 24 subjects, who had not been informed about the presence of MCS signals or the implication of the signal pictures prior to the experiment. Subjects were presented with realistic MCS sequences indicating either a speed recommendation or the closure of the lane presently used by the subject (the middle lane) which would require a lane change. The results indicated that subjects responded spontaneously and consistently to the different signal sequences. At sequences indicating a speed recommendation, speed was actually lower than it was on road sections with no speed recommendation, but was somewhat higher than the speed recommended on the signboard. Except in 3 of 768 sequences, indicating the closure of the driving lane, subjects changed lane upstreams of the closed-lane signboard. However, at the end of signal sequences most subjects also changed back to the middle lane (in which they were instructed to normally drive) upstreams the end-of-closure signboard. This behaviour suggested that the subjects had hardly grasped the idea that a signboard was in force until the position of the next one. A small number of unmotivated lane changes and a relatively high number of heavy brake reactions were also observed. Unmotivated lane changes were related to signal sequences with speed recommendations, whereas about half of the heaviest brake reactions could be related to signal sequences presenting a closed-lane symbol on the very first signboard in a sequence. A questionnaire after the experiment showed that subjects were consistent in explaining the implication of the different signal pictures. The majority observed the speed recommendation for the legal speed limit and the majority also claimed that a signal picture was in force as soon as it was visible. This may explain the observed tendency to change lane as soon as the end-of-closure symbol was visible unless prohibited by the presence of a hindrance in this lane. (A)
Abstract