The Victorian Intelligent Speed Assist and Heavy Vehicles Trial: Analysis of Device Acceptability and Influence on Speed Choice

The road safety benefits of Intelligent Speed Assist (ISA) have been demonstrated in passenger car trials. These benefits, however, have yet to be replicated in the heavy vehicle (trucking) industry. This small-scale trial conducted by the Transport Accident Commission (TAC) in collaboration with the Victorian Transport Association (VTA) with the cooperation of several heavy vehicle transport companies sought to assess the relative merits of ISA in terms of driver acceptability, speed choice, and fuel consumption. The study was a pre-post design. Prior to the installation of the ISA device, a GPS device was fitted to six heavy vehicles and vehicle speed and trip characteristics were continuously recorded. An advisory ISA device was then installed for a period of four to six weeks. Seven drivers participated in the trial and completed a survey before and after the trial. Prior to the study, six of the seven drivers stated they would find a device that would assist their speed choice to be useful, while four believed a device that would prevent them speeding would also be valuable. Following the trial, six drivers reported finding the system helpful in preventing them from speeding, rating it as 5 or above on the 10 point scale. Opinions were more divided in terms of the accuracy of the speed limit map, with two drivers rating it as very poor. Analysis of speed data indicated mixed benefits of ISA with a reduction of up to 21% in the odds of travelling over the posted speed limit; however reductions were speed zone dependent. ISA was most effective in improving compliance at the higher speed zones (≥80km/h) and not at all for the mid-level speed zones. Analysis of the speed data indicated an increase in the mean speed in the midlevel speed zones but a reduction in the lower and higher speed zones. Device acceptability appears to play some role in the effectiveness of advisory ISA systems, however the relationship is complex. Further work that explores the relationship between acceptability of ISA and compliance with the assigned speed limit is required.