Evaluating the Benefits of Active Speed Limiters and Comparison to Other Safety Measures.
T Toledo, S Hakkert, Technion -Israel Institute of Technology, IL; G Albert, Holon Institute of Technology, IL
This paper evaluates the impact of a wide installation of active speed limiters on traffic flow characteristics and on safety using a microscopic traffic simulation model, which captures the impact both on equipped and non-equipped vehicles.
Speed limiters, which control the maximum speeds of equipped vehicles, have been proposed in recent years as efficient and powerful tools of speed management. Active speed limiters directly control speed by applying counter force on the gas pedal or through the engine fuel injection system. Several European countries currently consider new legislation that would mandate installation of active speed limiters in various types of vehicles, especially commercial ones. For example, in the UK, all vehicles with more than eight passenger seats and goods vehicles with design weights over 3.5 Tons will be required to be equipped with speed limiter by 2008. With the current costs of the various technologies and related infrastructure, a wide installation of speed limiters is likely to be feasible if it is based on simpler pre-set systems rather than intelligent speed adaptation (ISA).
Several studies evaluated the impact of active speed limiters on driving behavior using field experiments and driving simulators. These studies found that speed limiters are effective in controlling travel speeds and that they can also reduce the variability of speed. However, these studies were conducted with relatively small samples that could not capture the network-wide impact of speed limiters. A wide installation of speed limiters would affect not only the equipped vehicles, but also the behavior of other vehicles. A network-wide evaluation of speed limiters would require large-scale field tests, which may be prohibitively expensive.
This paper describes the use of a microscopic traffic simulation model to evaluate the impact of a wide installation of active speed limiters on traffic flow characteristics and on safety. The traffic simulator models the acceleration and lane changing behavior of individual vehicles in detail, and so captures not only the impact of speed limiters on equipped vehicles but also the interaction between equipped and non-equipped vehicles and the resulting impact on non-equipped vehicles. In the experiment, we evaluate the impact of various factors that include the limiter set speed, the mean desired speed, congestion level. The impacts are quantified in terms of the average and distribution of speeds, the numbers of lane changes performed and the predicted impact on the rates of injury and fatal accidents. We also evaluate the impact of the speed limiters penetration rates on these statistics.
The simulation results show that speed limiters have significant effects on the speeds driven, the variability of speeds and frequency of lane changing, but not on traffic flows. Active speed limiters can reduce traffic speeds by as much as 10%. This result is comparable with field and driving simulator evaluations. The variability of traffic speeds may also significantly be reduced when speed limiters are used, especially for the higher desired speeds and congestion levels. Consequently, a significant desired reduction in the accident rate might be reached. Speed limiters also have an impact on the number of lane changes drivers undertake. Generally, the impact of speed limiters is more pronounced when their settings are more restrictive compared to uncontrolled traffic speeds in the section. They are also generally most effective in the middle range of congestion levels, where they have a moderating effect not only on equipped vehicles but also on non-equipped ones.
Association for European Transport