Impact of Active Speed Limiters on Traffic Flow and Safety: Simulation-Based Evaluation (original) (raw)
Related papers
The effects of in-car speed limiters: field studies
2001
Field trials in three European countries, the Netherlands, Spain and Sweden were carried out in order to investigate the eects of an in-car speed limiter. The trials were carried out on urban and rural roads including motorways. A so-called unobtrusive instrumented car was used, where all the measuring equipment was hidden. All the speed limit categories in the respective countries, ranging from 30 to 120 km/h were included. The results showed that the eects of the limiter were greatest in free driving conditions outside platoons. However, the limiter also had eects in congested trac. Momentary high speeds were suppressed eectively, which resulted in less variation of speeds. Approach speeds at roundabouts, intersections and curves became smoother, car-following behaviour became safer in the speed range of 30±50 km/h. On the other hand, in the speed range of 70±90 km/h a slightly higher number of short time-gaps suggested less safe car-following behaviour. Other negative behavioural eects were slightly increased travel time and the increased frustration and stress for the drivers caused by the limiter. The majority of the subjects accepted the speed limiter as a driver-operated system. Half of the drivers would accept the limiter voluntarily in their cars. Ó 1th.se (A. Va Ârhelyi).
EVALUATING THE BENEFITS OF ACTIVE SPEED LIMITERS AND COMPARISON TO OTHER SAFETY MEASURES
This paper evaluates the benefits of equipping European light goods vehicles (LGV) with active speed limiters and compares these benefits with those of other safety measures. In evaluating the impact of speed limiters we use a microscopic traffic simulation model which 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. The simulation results indicate that speed limiters can reduce traffic speeds by as much as 10%. Consequently, a significant reduction in the accident rate might be achieved. The safety effects and associated costs of active speed limiters are evaluated and compared to five other safety measures using a cost benefit analysis (CBA).These measures include the installation of electronic stability protection (ESP), digital tachographs, event data recorders (EDR), seat-belt reminders and seat-belt lock systems and the implementation of a professional driver training program. The CBA analysis yielded B/C ratios greater than 1 for a speed limiter set at 100 km/h, for a professional driver training programme and for devices to increase seatbelt wearing, indicating that these safety systems are economically justified for LGVs.
Impacts of Speed Limits and Information Systems on Speed Choice from a Safety Perspective
Driving a vehicle is considered a demanding task in a complex dynamic environment. For instance, driving a vehicle on urban roads, where motorized vehicles meet vulnerable road users (VRUs) creates a multifaceted environment with difficult trade-offs and interactions. Additionally, in-vehicle technology developments are being introduced to ease drivers with the driving task. However, these developments are changing "traditional" driving increasing drivers' response in terms of information processing, thus making the driving task more demanding in some respects. Therefore, the aim of the present research is to further investigate drivers' speed choice under varying traffic management regulations and in-vehicle warning systems. Paper I is based on a follow-up study conducted in order to investigate the impact on drivers' speed choice of changing the posted speed limit (PSL) in urban areas. Speed choice is crucial due to conflicts between motorized traffic and VRUs. Extensive field studies were conducted changing the PSL of 50 km/h to 40 km/h or 60 km/h. Additionally, road characteristics were taken into account, thus analyzing the impact of different traffic management regulations and geometric characteristics. The results showed a speed threshold to introduce PSLs reductions. The largest impacts of PSL changes were observed on higher road network classes and speed choice was heavily influenced by several road characteristics. Paper II investigates the free-flow speed distribution in urban areas. A probabilistic approach is presented to distinguish free-flow vehicles from constrained vehicles on urban roads. A headway range was defined where the probability for a given vehicle to be constrained was estimated. A logit model was used to estimate the regime the driver was in. The results showed a crucial headway range between 4 and 7 seconds where the probability to be constrained dropped from approximately 90 to 10 percent. Paper III describes the impact of in-vehicle technologies on speed behaviour. The COOPERS I2V Cooperative System was evaluated at the aggregate level at various levels of traffic demand and penetration of the system. A factorial experimental study was conducted with two factors and three levels. Traffic performance indicators such as speed, density, delay and travel times were considered for evaluation purposes. The results showed that driving with the system was characterized by smoother speed decelerations. Meanwhile, traffic congestion reduced the impact of the system and higher penetration levels improved the traffic operation.
FIELD TRIALS WITH IN-CAR SPEED LIMITER
SUMMARY Effects of an in-car speed limiter were investigated in three European countries, the Netherlands, Spain and Sweden representing different regions and driving cultures. The study was carried out in urban and surrounding areas. Most of the European speed limit categories, ranging from 30 km/h to 120 km/h were included. The effects of the limiter were greatest in free driving conditions outside platoons. Ho w- ever, the effects of the limiter were also seen in congested traffic, even though milder than in free dri v- ing. The effects were greatest in suppressing momentary high speeds, and consequently the variation of speeds was clearly reduced by the limiter. Some negative behavioural effects were also found. These were usually slightly higher number of short time-headways and the increased frustration and stress caused by the limiter. The acceptance of the limiter increased somewhat after trying it out. However, clearly less than half of the drivers would take the limiter vo...
Transportation Research Record: Journal of the Transportation Research Board, 2013
Control of traffic by a variable speed limit (VSL) has been researched for a long time, but there is a lack of consensus on its safety and operational benefits and on the impact of driver compliance. This study provides quantitative evaluations of these benefits and shows the importance of driver compliance with VSLs. VISSIM and the technique of simulated vehicle conflicts (Surrogate Safety Assessment Model) were used in the study. To validate the safety analysis, an attempt was made to correlate the simulated vehicle conflicts with historic crashes. Three scenarios of traffic conditions were considered: heavily congested, lightly congested, and uncongested. Each scenario was further examined under four driver compliance levels: low, medium, high, and very high. The results con-firmed that the VSL had safety and operational benefits for motorway traffic. The system had the highest safety benefits during highly congested traffic conditions, followed by lightly congested conditions, a...
Transportation Research Part C: Emerging Technologies, 2015
Speeding is an aggravating factor in all crashes. The relation between speed and safety depends on two fundamental aspects: the relationship between speed and the crash risk and the relationship between speed and the crash severity. Higher speeds imply greater difficulty in driving task and therefore a greater crash risk. At higher speeds, the time to react to changes in the environment is shorter, the stopping distance is greater, and the vehicle's manoeuvrability is reduced. However, the greatest effect of high speed is on the consequences of the crashes. The higher the collision speed the more severe the consequences in terms of injury and material damage. This is because the energy dissipated in a crash increases with the square of collision speed. At a higher impact speed, more energy is released when colliding with another vehicle, road user or obstacle. Part of this energy is absorbed by the vulnerable human body. Furthermore, also speed variability affects safety. The greater the speed variability, the greater the crash frequency (Aarts and and the crash severity (Yu and Abdel-Aty, 2014a, 2014b).
In this paper, we evaluated the effects on speed and safety of the point-to-point (P2P) speed enforcement system activated on the urban motorway A56 in Italy. The P2P speed enforcement is a relatively new approach to traffic law enforcement that involves the calculation of the average speed over a section. To evaluate the speed effects, we performed a before–after analysis of speed data investigating also effects on non-compliance to speed limits. To evaluate the safety effects, we carried out an empirical Bayes observational before-and-after study. The P2P system led to very positive effects on both speed and safety. As far as the effects on the section average travel speeds, the system yielded to a reduction in the mean speed, the 85th percentile speed, the standard deviation of speed, and the proportion of drivers exceeding the speed limits, exceeding the speed limits more than 10 km/h, and exceeding the speed limits more than 20 km/h. The best results were the decrease of the speed variability and the reduction of the excessive speeding behaviour. The decrease in the standard deviation of speed was 26% while the proportion of light and heavy vehicles exceeding the speed limits more than 20 km/h was reduced respectively by 84 and 77%. As far as the safety effects, the P2P system yielded to a 32% reduction in the total crashes, with a lower 95% confidence limit of the estimate equal to 22%. The greatest crash reductions were in rainy weather (57%), on wet pavement (51%), on curves (49%), for single vehicle crashes (44%), and for injury crashes (37%). It is noteworthy that the system produced a statistically significant reduction of 21% in total crashes also in the part of the motorway where it was not activated, thus generating a significant spillover effect. The investigation of the effects of the P2P system on speed and safety over time allowed to develop crash modification functions where the relationship between crash modification factors and speed parameters (mean speed, 85th percentile speed, and standard deviation of speed) was expressed by a power function. Crash modification functions show that the effect of speed on safety is greater on curves and for injury crashes. Even though the study results show excellent outcomes, we must point out that the crash reduction effects decreased over time and speed, speed variability, and non-compliance to speed limits significantly increased over time. To maintain its effectiveness over time, P2P speed enforcement must be actively managed, i.e. constantly monitored and supported by appropriate sanctions.
Driving with intelligent speed adaptation: Final results of the Belgian ISA-trial
Transportation Research Part A-policy and Practice, 2007
In October 2002 the first ISA-trial in Belgium was started in Ghent. 34 cars and 3 buses were equipped with the "active accelerator pedal". In this system a resistance in the accelerator is activated when the driver attempts to exceed the speed limit. If necessary, the driver can overrule the system. The main research goals of the trial in Ghent were to evaluate the effects of ISA on speed-change, traffic safety, drivers' attitude, behaviour and drivers' acceptance. To study these effects of the ISA-system both surveys and logged speed data were analyzed. In the surveys drivers noticed that the pedal assisted them well in upholding the speed limits and that the system increased driving comfort. Most important drawbacks were technical issues.
Journal of the Eastern Asia Society for Transportation Studies, 2011
Recently, the concern over ISA has been growing in European countries. Introducing ISA into residential roads in Japan may significantly improve the traffic safety of bicycles and pedestrians. However, ISA also represses the convenience of drivers. The aim of this study is to develop a method for evaluating the burdens of drivers due to Mandatory ISA. Firstly, the factors affecting the speed selection of drivers on residential roads is analyzed based on a driving experiment. Secondly, based on the total cost minimization concept, a speed selection model which considers the trade-off between perceived accident cost and delay cost is developed. Then, the total cost which drivers perceive when driving at a certain speed under a certain road environment condition is estimated. The result shows that the perceived total cost will increase by 0.5% ∼ 6.5% and 19% ∼ 39% with the ISA limiting to 30 km/h and 20 km/h, respectively.
Improving homogeneity by dynamic speed limit systems
Accident Analysis & Prevention, 2010
Homogeneity of driving speeds is an important variable in determining road safety; more homogeneous driving speeds increase road safety. This study investigates the effect of introducing dynamic speed limit systems on homogeneity of driving speeds. A total of 46 subjects twice drove a route along 12 road sections in a driving simulator. The speed limit system (static-dynamic), the sophistication of the dynamic speed limit system (basic roadside, advanced roadside, and advanced in-car) and the situational condition (dangerous-non-dangerous) were varied. The homogeneity of driving speed, the rated credibility of the posted speed limit and the acceptance of the different dynamic speed limit systems were assessed.