Field trials with in-car speed limiter

Within the framework of the EU-financed project MASTER field trials with in-car speed limiter were carried out in three “region-typical” countries: Sweden, the Netherlands, and Spain. The speed limiter is an active gas pedal which provides a gas pedal counter-force whenever the driver tries to depress the pedal beyond a pre-set speed limit. Twenty subjects per country drove two times along the test route: once with the speed limiter on and once off. The length of the test routes was 20 - 30 km consisting of urban street network, rural roads, motorway stretch. Different speed limits typical for urban (30 or 50, 60 km/h) and inter-urban roads (80 - 120 km/h) were included. The experiment was done with an instrumented vehicle. The speed limiter was automatically triggered by transmitters attached to speed limit signs. The independent variables were the conditions (speed limiter on/off) and the between subject factors such as country (where the test drives took place), sex and age group. (The dependent variables were speed, car-following behaviour, give-way behaviour, driver workload, and driver opinions.

The results revealed that the speed limiter reduced speeds significantly on roads with speed limits from 30 to 70 km/h. No significant changes could be shown on 80 - 120 km/h roads due to more frequent platoon driving. Other positive effects were found in terms of: a) decreased speed variance; b) smoother approach speeds at roundabouts, intersections and curves; c) increased time-gaps in the speed interval 30 - 50 km/h indicating that following behaviour became safer when driving with the speed limiter. There were some negative effects in terms of: a) decreased time-gaps in car-following situations on rural roads in the speed interval between 70 and 90 km/h indicating a less safe following behaviour; b) increased travel time and c) increased frustration and stress, less patience. No significant effects were found on: a) turning speeds; b) giving way behaviour and c) experienced subjective safety when driving with the speed limiter. The conclusion from the experiment is that automatic speed limiting via in-car equipment is promising within built-up areas. The acceptance of the system amongst drivers is the highest there.