On-road evaluation of Intelligent Speed Adaptation, Following Distance Warning and Seatbelt Reminder Systems: final results of the TAC SafeCar project

Monash University Accident Research Centre - Report #253 [2006]

Authors: Michael A. Regan, Thomas J. Triggs, Kristie L. Young, Nebojsa Tomasevic, Eve Mitsopoulos, Karen Stephan, & Claes Tingvall

Full report in .pdf format [1.9MB]
Volume 2 - Appendices .pdf format [10.3MB]


The TAC SafeCar project is one of a growing number of on-road studies evaluating the potential road safety benefits of in-vehicle Intelligent Transport Systems (ITS). The project had several aims: to evaluate the technical operation of a number of ITS technologies with high estimated safety potential; to assess the acceptability to drivers of these technologies; and to evaluate, in an on-road setting, the impact of these technologies, alone and in combination, on driver performance and safety. The project also involved a study that examined, in an advanced driving simulator, the effects on driving performance of two variants of Intelligent Speed Adaptation (ISA). This report documents the design, methodology and final outcomes of Phase 4 of the project, which involved the deployment and on-road evaluation of four ITS technologies equipped to 15 Ford passenger cars (referred to as ‘SafeCars’). The four technologies were: Intelligent Speed Adaptation (ISA); Following Distance Warning (FDW); Seatbelt Reminder (SBR) and Reverse Collision Warning (RCW). Each SafeCar was also equipped with Daytime Running Lights. Twenty-three fleet car drivers (15 treatment and 8 control drivers) participated in the on-road trial. Each participant drove a SafeCar for at least 16,500 kilometres. During the trial, the treatment drivers were exposed to all four ITS technologies, while the control drivers were exposed to the SBR and RCW systems only. Each SafeCar was equipped with a data logging system which automatically recorded a range of driving performance measures. This report presents the findings that derived from the logged driving data and from the subjective data on drivers’ perceived acceptability and usability of the SafeCar systems.

Overall, the ISA, FDW, and SBR systems had a positive effect in promoting safer driving performances. The ISA system reduced mean, maximum and 85 th percentile speeds, and reduced speed variability in most speed zones. ISA also reduced the percentage of time drivers spent travelling above the speed limit, and did not increase travel times. The FDW system significantly increased mean time headway and reduced time headway variability. Driver and passenger interaction with the SBR system led to large decreases in the percentage of trips where occupants were unbelted, in the percentage of total driving time spent unbelted, and in the time taken to fasten a seat belt in response to the seatbelt warnings. However, the positive effects on driving performance induced by these systems persisted only while the systems were activated, with drivers reverting back to their old driving habits after the systems were deactivated, highlighting the effectiveness of the systems while they are active. There was little evidence of any negative behavioural adaptation to the systems; that is, there was no indication of increased risk taking associated with use of the SafeCar systems.

A significant reduction in fuel consumption was found, but only in 80km/h zones when the ISA and FDW systems combined were active. Carbon Dioxide emissions also decreased significantly, when both ISA and FDW were jointly active in 80 km/h zones. A significant reduction in Nitrogen Oxide and Hydrocarbonates emissions was found in 80 km/h zones when the ISA system alone was active. Significant reductions in Nitrogen Oxide and Hydrocarbonates emissions were also found in 60 km/h (Nitrogen Oxide only) and 80 km/h zones when both the ISA and FDW systems were jointly active.

Based on the logged data, the ISA system by itself is expected to reduce the incidence of fatal crashes by up to 8 percent and serious injury crashes by up to 6 percent. When combined with FDW, the ISA system is expected to reduce fatal and serious injury crashes by 9 and 7 percent, respectively. For the FDW system, the percentage of driving distance spent in rear-end collision mode (that is, where the vehicle would collide with the lead vehicle) is expected to reduce by up to 34 percent with use of the FDW system alone, under conditions where the lead vehicle is braking at a moderate rate. Finally, HARM analysis based on the results of this study revealed that use of the SBR system is also expected to save the Australian community approximately $335 million per annum in injury costs.

The ISA, FDW, SBR and RCW systems were generally rated as being useful, effective and socially acceptable. This was the case both prior to, and after, experience with the systems. The FDW system was rated as more effective at the end of the study, although after experience with the system, less of the participants were inclined to keep it. The systems were also found to be usable, although some drivers recommended alternative positions for the visual warning display. The RCW system was the most successful at reducing the level of workload felt by drivers. The SBR system also led to decreased workload, but only for the treatment drivers. Positively, the ISA and FDW systems did not increase the perceived level of workload participants experienced while driving. There was a positive effect of the SBR and FDW systems on road safety awareness: after using the systems, drivers were more likely to be aware of the requirement to wear a seatbelt when travelling slowly, and to adhere to the recommended following distance.

Potential barriers to driver acceptance of the systems were identified. Participants reported that they would lose trust in systems if they gave unreliable warnings. The cost of the systems is a potential barrier to acceptance, particularly maintenance and service costs. Some participants found the auditory warnings annoying, but suggestions were made as to how they could be made more acceptable. It is encouraging to note that participants found the systems acceptable in terms of level of control; they did not feel that they would rely too strongly on the systems at the expense of their own judgment. Also, they did not think the systems would distract them from their driving.

Sponsoring organisations - Victorian Transport Accident Commission (TAC); Ford Motor Company of Australia