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Author: Timothy J. Gates Publisher: ISBN: Category : Speed limits Languages : en Pages : 122
Book Description
As of July 2016, Montana was the only state to maintain a differential speed limit on two-lane two-way rural highways, utilizing a daytime statutory speed limit of 70 mph for cars and light trucks and 60 mph for trucks exceeding a one-ton payload capacity. Although differential speed limits are common on freeways, the use of differential limits on two-lane roadways presents unique safety and operational issues due to passing limitations and subsequent queuing, and prior research on such issues is scarce. Consequently, research was performed to evaluate the safety and operational impacts associated with the aforementioned differential speed limit on rural two-lane highways in Montana, particularly when compared to a uniform 65 mph speed limit. A series of field studies were performed on two-lane rural highways in Montana, which predominately possessed the 70 mph/60 mph differential speed limit, and in neighboring states where uniform 65 mph speed limits prevailed. The locations with 65 mph speed limits generally displayed less variability in travel speeds, shorter platoon lengths, less high-risk passing behavior, and fewer crashes. Surveys were performed to determine the speed limit policy preferences among motorists and members of the trucking industry in Montana. Although motorist support for the uniform 65 mph speed limit was mixed, the trucking industry strongly supported the uniform 65 mph limit over the current differential limit. Overall, the collective findings support transitioning to a uniform 65 mph speed limit on two-lane rural highways in Montana. Selective implementation of this new speed limit is advised initially, and candidate highways should possess relatively high traffic volumes, relatively high truck percentages, and limited passing opportunities.
Author: Timothy J. Gates Publisher: ISBN: Category : Speed limits Languages : en Pages : 122
Book Description
As of July 2016, Montana was the only state to maintain a differential speed limit on two-lane two-way rural highways, utilizing a daytime statutory speed limit of 70 mph for cars and light trucks and 60 mph for trucks exceeding a one-ton payload capacity. Although differential speed limits are common on freeways, the use of differential limits on two-lane roadways presents unique safety and operational issues due to passing limitations and subsequent queuing, and prior research on such issues is scarce. Consequently, research was performed to evaluate the safety and operational impacts associated with the aforementioned differential speed limit on rural two-lane highways in Montana, particularly when compared to a uniform 65 mph speed limit. A series of field studies were performed on two-lane rural highways in Montana, which predominately possessed the 70 mph/60 mph differential speed limit, and in neighboring states where uniform 65 mph speed limits prevailed. The locations with 65 mph speed limits generally displayed less variability in travel speeds, shorter platoon lengths, less high-risk passing behavior, and fewer crashes. Surveys were performed to determine the speed limit policy preferences among motorists and members of the trucking industry in Montana. Although motorist support for the uniform 65 mph speed limit was mixed, the trucking industry strongly supported the uniform 65 mph limit over the current differential limit. Overall, the collective findings support transitioning to a uniform 65 mph speed limit on two-lane rural highways in Montana. Selective implementation of this new speed limit is advised initially, and candidate highways should possess relatively high traffic volumes, relatively high truck percentages, and limited passing opportunities.
Author: Eric T. Donnell Publisher: ISBN: Category : Speed limits Languages : en Pages : 127
Book Description
The purpose of this project is to provide the Montana Department of Transportation (MDT) with a better understanding of the operational and safety impacts of setting posted speed limits below engineering recommended values. This practice has been performed on Montana roadways for a variety of reasons but the safety and operational impacts are largely unknown. An Empirical Bayes observational before-after study found that there is a statistically significant reduction in total and fatal and injury crashes at sites with engineering speed limits set 5 mph lower than engineering recommendations. At locations with posted speed limits set 10 mph lower than engineering recommendations, there was a decrease in total crash frequency, but an increase in fatal and injury crash frequency. The safety effects of setting posted speed limits 15 or 25 mph lower than engineering recommendations is less clear, because the results were not statistically significant, due to the small sample size of sites available for inclusion in the analysis. An operating speed evaluation found that, when the posted speed limit was set only 5 mph lower than the engineering posted speed limit, drivers tend to more closely comply with the posted speed limit. Compliance tends to lessen as the difference between the engineering recommended posted speed limit and the posted speed limit increases. The practice of light enforcement, which was defined as highway patrol vehicles making frequent passes through locations with posted speed limits set lower than engineering recommendations, appeared to have only a nominal effect on vehicle operating speeds. Known heavy enforcement, defined as a stationary highway patrol vehicle present within the speed zone, reduced mean and 85th-percentile vehicle operating speeds by approximately 4 mph.
Author: David L. Harkey Publisher: ISBN: Category : Speed limits Languages : en Pages : 78
Book Description
The objectives of this study were to determine whether differential or uniform speed limits are more beneficial to transportation safety and traffic operations on Interstate highways. The approach to achieving this objective was to examine speed and accident data from States employing both types of limits. Speed data were collected in 12 States at rural and urban locations representing all speed limits currently established on the Interstate highway system for cars/trucks, i.e., 55/55 mi/h (89/89 km/h), 65/55 mi/h (105/89 km/h), 65/60 mi/h (105/97 km/h), and 65/65 mi/h (105/105 km/h). Accident data were obtained from nine States which were geographically distributed across the country and representative of all rural Interstate speed limits currently established. For the speed data collected, a number of measures of effectiveness (MOEs) were examined including mean speed, speed variance, compliance, and speed distribution measures. For the accident data collected, types of crashes were examined (e.g., rear-end) along with vehicle type involvement (e.g., car-into-truck) and crash severity. This final report summarizes the effects of uniform and differential speed limits on transportation safety and traffic operations as determined by the examination of speed and accident data.
Author: American Association of State Highway and Transportation Officials. Operating Subcommittee on Traffic Engineering Publisher: ISBN: Category : Speed limits Languages : en Pages : 66
Author: Publisher: ISBN: Category : Roads Languages : en Pages : 89
Book Description
"To compare the safety effects of a uniform speed limit (USL) for all vehicles as opposed to a differential speed limit (DSL) for cars and heavy trucks, detailed crash data, speed monitoring data, and traffic volumes were sought for rural interstate highways in 17 States for the period 1991 to 2000. Conventional statistical tests (analysis of variance, Tukey's test, and Dunnett's test) were used to study speed and crash rate changes in the four policy groups. A modified empirical Bayes formation was used to evaluate crash frequency changes without presuming a constant relationship between crashes and traffic volume"--Technical report documentation page.
Author: Haggai Davis Publisher: ISBN: Category : TRANSPORTATION Languages : en Pages : 0
Book Description
"The National Highway Traffic Safety Administration (NHTSA) reported that 37,461 people died in 2016 on US roads, marking the second year in a row that the number has increased [1]. Many transportation-related agencies have adopted a “Vision Zero” or “Towards Zero Deaths” campaign aiming to eliminate the need for that statistic. Speed can often play a role in fatalities, so setting the proper speed limit for roadways is important in saving lives. American speed limits have a complicated history over the past 50 years, which hinders researchers’ ability to look at much longer stretches of data and draw conclusions about determining the best speed limit strategy. From 1973 to 1987, the maximum speed limit was 55 MPH. After that, Congress raised the allowable limit to 65 MPH. It was not until 1995 that states had full discretion over setting an appropriate limit. Some states raised the speed limit for all vehicles equally – a uniform speed limit (USL). Others raised speeds for trucks less than that of cars – a differential speed limit (DSL). On the surface, the benefit of a DSL seems intuitive, lowering the speeds for big trucks would reduce the severity of accidents. However, it also has the effect of increasing total variance in speed which increases the number of accidents. This report aims to explore the literature published about these issues and to inform decision makers about the factors to be weighed when considering DSL versus USL. It was prepared in response to a request in the 2017 session of the Louisiana House of Representatives where the Louisiana Department of Transportation and Development (DOTD) was asked to “study the safety and operational impacts of differential speed limits on interstate highways” (House Concurrent Resolution 112). Thus, the purpose of this study is to inform the Louisiana Legislature about the documented benefits and costs of a differential speed limit for passenger cars versus larger vehicles specifically with regards to the topics of Safety, Mobility and Operations, Fuel Consumption and Emissions, and Truck Determination as outlined in HCR 112."--Introduction.
Author: Megat Usamah Bin Megat Johari Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 0
Book Description
Fatal crashes have been increasing, both in Michigan and across the United States, despite continuing improvements in roadway design, vehicle safety, and other areas. Various factors may have contributed to this trend, including increased in-vehicle distractions, higher speed limits, legalization of marijuana, and other factors. Studies have suggested that driver error is a critical reason associated with more than 90 percent of all traffic crashes. Driver behavior can be improved by several engineering strategies, such as the use of better and more efficient traffic control devices, such as signs, signals, and pavement markings. To that end, this research assesses the operational and safety impacts of a series of traffic control devices.The use of dynamic message signs (DMS) as a medium to display safety messages to drivers has become popular among transportation agencies. Despite their widespread use, evaluations as to the resultant impacts on traffic crashes have been very limited. This study addresses this gap in the extant literature and assesses the relationship between traffic crashes and the frequency with which various types of safety messages are displayed. A series of count models are estimated to examine total, speeding-related, and nighttime crashes based upon historical messaging data while controlling for other site-specific factors. Ultimately the results provide important insights regarding messaging strategies for transportation agencies. This research also evaluates driver response to advisory speed signs. Posted speed limit signs are used to inform drivers of the legal maximum allowable speed. In contrast, advisory speed signs provide recommendations to drivers as to safe travel speeds at specific roadway locations. Various studies have investigated the safety impacts of speed limit changes, particularly on high-speed rural highways. One area of particular concern on such roadways is the approach to exit ramps that require substantive speed reductions, such as loop ramps. To date, there has been limited research examining the safety impact of the differential between the mainline speed limit and the lower exit ramp advisory speeds. This study addresses this gap through the estimation of a series of safety performance functions. The findings from this study show the safety of these locations is related to speed differential, as well as other factors such as the length of the upstream deceleration lane. These factors should be considered when considering speed limit policy impacts in the vicinity of full and partial cloverleaf interchanges.Lastly, this study assesses the use of dynamic speed feedback sign (DSFS) as a means to reduce vehicle speeds in speed transition zones, where speeds are reduced as drivers enter rural communities. DSFS have been evaluated in several settings, including high-speed exit ramps and horizontal curves. However, research is limited as to the effectiveness of this sign for other purposes, such as these high-speed transition areas. This is particularly important as the limits on some of these roadways have recently been increased, making speed control a particular concern. This study addresses this gap through a before-and-after evaluation of DSFS at five different sites in northern Michigan. A series of speed models were estimated, which provide insights on the effectiveness of DSFS.
Author: Timothy J. Gates
Author: Timothy J. Gates
Author: Eric T. Donnell
Author: United States. National Highway Traffic Safety Administration
Author: David L. Harkey
Author: 
Author: American Association of State Highway and Transportation Officials. Operating Subcommittee on Traffic Engineering
Author: 
Author: 
Author: Haggai Davis
Author: Megat Usamah Bin Megat Johari