Safety Implications of Mandated Truck Speed Limiters on Freeways (original) (raw)
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Impact of Active Speed Limiters on Traffic Flow and Safety: Simulation-Based Evaluation
2. Preset or dynamic limiter-set speeds. Preset systems use a fixed set speed. Dynamic systems, or intelligent speed adapters (ISAs), use real-time information to adapt the set speed to posted speed limits in various road facilities and to road and weather conditions. Although ISAs provide better control of speed, they also require communication between the vehicle and roadside beacons or the use of the Global Positioning System in order to obtain the dynamic speed limit information. These systems therefore require more expensive road infrastructure and installations in the vehicle.
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...
Operational and Safety Evaluation of Freeways with Posted Minimum Speed Limit
Journal of the Transportation Research Forum, 2010
An operational and safety evaluation was conducted in relation to the posting of the minimum speed limit of 40 mph and the maximum speed limit of 70 mph on the Florida rural interstate freeway system. The results showed that 57% of the recorded vehicles exceeded the maximum speed limit. Additionally, while only 0.14% of recorded vehicles had speeds below the 40 mph posted minimum speed limit, 9% of crash-involved vehicles were estimated to have speeds below 40 mph. The overrepresentation of slow-moving vehicles in the crash data suggests that even a small proportion of under-40-mph vehicles can have negative implications on safety. Thus, regulation of vehicle speeds at the lower end of the speed distribution is equally important. The second order polynomial model developed to estimate the risk of a vehicle being involved in a crash as a function of the speed deviation from the mean speed of traffic indicated that the minimum risk occurred when the driving speed was 8 mph above the m...
Assessing the Impact of Raising Truck Speed Limits on Traffic Safety
2020
Author(s): Musabbir, Sarder Rafee; Zhang, Michael, PhD | Abstract: This project used statewide crash and traffic data to develop four statistical models to determine the safety impacts of increasing speed limits for trucks and cars on California highways. The models examined whether various factors about crashes—including average traffic speed, involved vehicle type, weather, etc.—correlated with other crash characteristics of particular policy relevance: namely, fatal crash, truck-related crash, speeding-related crash, and crash severity. The fatal crash model was then used to predict the probability of fatal crashes in urban and rural areas under four possible speed limit policies: (A) maintaining the existing speed limits of 65 mph for cars and 55 mph for trucks; (B) increasing each of these by 5 or 10 mph; (C) increasing the current truck speed limit to equal the car speed limit of 65 mph; (D) following policy C and then increasing the uniform 65 mph speed limit by 5 or 10 mph. ...
Its Implication on Setting Variable Speed Limits on Freeways
2012
Speed-flow relationships for a typical basic freeway segment are well understood at present and are documented by the successive editions of the Highway Capacity Manual. All recent freeway studies show that speed on freeways is insensitive to flow in the low to mid range. Increase in flow and density without reduction in speed has a significant influence on safety. Constructive discussion of this influence, however, is largely absent from extant literature. Empirical examination of the relationship between flow/density, speed and crash rate on selected freeways in Colorado suggests that as flow/density increases crash rate initially remains constant until a certain critical threshold combination of speed and density is reached. Once this threshold is exceeded the crash rate rapidly rises. The rise in crash rate may possibly be explained by the fact that compression of flow without notable reduction in speed produces headways so small that it becomes very difficult or impossible to compensate for driver's error to 14 avoid a crash. In addition to calibrating corridor specific SPFs relating crash rate to hourly volume/density and speed this paper proposes a variable speed limit (VSL) 16 algorithm intended to slow traffic down in real time in advance of a high speed-high density operational regime. Deployment of such an algorithm has the potential to improve safety and reduce travel time variability. 19 20 21 TRB 2012 Annual Meeting Paper revised from original submittal.
To improve traffic operation and safety, several states have implemented truck lane restriction and differential speed limit policies on freeways. The State of Louisiana introduced such restrictions on an 18-mile elevated four-lane rural segment of Interstate 10 (I-10) in response to an 11-vehicle crash in September 2003. The new control policies, implemented in 2005, have restricted trucks to the right lane only and reduce their speed limit to 55 mph. At the same time the speed limit for passenger cars was also reduced from 70 mph to 60 mph. This paper highlights the findings of a survey to assess truck drivers' perceptions and opinions of these restrictive policies. Another objective of the survey was to solicit ideas and input for other potential strategies that could be useful to the drivers. Overall, the results showed that the truckers were not in favor of the restrictions and they did not perceive that a significant safety benefits were being gained from restrictions. In fact, it was apparent that they felt it was safer to have uniform and higher speed limits and freedom to select a travel lane.
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.
The safety implications of car-truck speed limits have not been adequately researched for two-lane highways. On two-lane highways speed controls can have a significant effect on vehicles interactions. Two different types of speed control strategies are considered: Uniform and Differential. Safety implications are considered using three overtaking-related indicators: Number of vehicles overtaking, 2) Percentage time spent in "desire to overtake mode", and 3) Average Time-to-Collision with the oncoming vehicle prior to returning to the original lane. Vehicle interactions affecting safety are estimated through the application of a calibrated microscopic traffic simulation model to a 6Km straight segment of two-lane highway.