In case of an incident on the motorway the road may be blocked for a considerable amount of time and traffic should be re-routed. However, it takes quite some time to install the detour. Therefore, it would be easy if route signs already indicate a permanent detour. At the moment, the Ministry of Transport, Public Works and Water Management is planning a number of permanent detours on different locations. To such a concept, a detour was indicated by signs on a test route. TNO Human Factors investigated the comprehensibility for road users in commission of the Transport Research Center (TRC) of the Ministry. Subjects had to follow the detour (which was indicates by a blue sign with a white number 6) with their own car which was instrumented with a GPS (Global Positioning System) and a laptop. This provided the opportunity to know whether and where subjects made errors along the route. After following the detour subjects were interviewed. Useful GPS data was collected of 79 subjects. Subjects were assigned to one of three groups: 29 subjects followed the route during the day, 25 subjects during peak hours (during these hours it was still light), and 25 subjects followed the route during the evening in the dark. The TRC had stated to accept the present way of indicating the detour only if 80% (or more) of the subjects would respond positively to this detour. For the experiment, this meant that 80% of the subjects should drive correctly without making route-errors and that 80% of the subjects should be positive about the detour in their interviews. The results showed that more than 80% of the subjects that followed the detour during the day and rush hour drove correctly (93% and 88% resp.). Less than 80% of the subjects that followed the route during the evening drove correct (76%). These percentages are based on the GPS data. When the (subjective) responses during the interviews are also taken into account, subjects were less positive than 80% (75,9%). So, based on the GPS data the criterion set by TRC is met in two out of three conditions. Normally detours are indicated by yellow signs with black numbers or letters, so subjects didn't expect the colour that was used (blue, but they probably wouldn't have expected any other colour). So in the beginning they started to look for yellow signs. The location of the signs was not systematic during the detour (they were sometimes located on the left side of the road, sometimes on the right side, sometimes at an intersection and sometimes on another sign before the intersection). Therefore, even when subjects knew what to look for, they still had to search on a number of possible locations. Also the presence of various other signs may cause that the 'detour sign' is not easily found. Most subjects preferred the detour sign on a direction sign before of an intersection (instead on a separate post or ANWB-post) and would follow the detour (and thus not try to find their own way). Based on the GPS data the criterion set by TRC is met in two out of the three conditions. When the subjective responses during the interviews are also taken into account (e.g., some indicated that they hadn't seen the sign and happened to follow the correct direction) then overall, subjects drove less than 80% correctly (75,9%). There are relatively simple improvements that can be made to improve this concept, such as showing an example of the detour sign on the motorway (at the exit) and using a systematic location of the signs during the detour. Certain aspects that could improve following the detour were not included in this study, such as the possibility to follow the main traffic flow, or being used to the detour sign. (Author/publisher)
Abstract