Author: Yacoub M. Najjar Publisher: ISBN: Category : Speed limits Languages : en Pages : 68
Book Description
On November 28, 1995, the National Highway System (NHS) Designation Act abolished the federal mandate for the National Maximum Speed Limit (NMSL) and returned the authority of establishing speed limits to the states. By the end of 1996, 32 states had passed laws to raise speed limits on various highways. Accordingly, Kansas' law increased speed limits on most of its highways in March 1996. The detailed research study reported herein concentrated on analyzing the before and after Kansas speed and accident databases. In regard to speed analysis, the t-test was applied to investigate whether significant increases in 85th percentile speeds were noted during the after period on both interstate and 2-lane rural highways.
Author: Sunanda Dissanayake Publisher: ISBN: Category : Languages : en Pages : 161
Book Description
Setting an appropriate speed limit is necessary to provide safe and efficient traffic operations for all road users. It must also be acceptable to the public and enforceable by police. Lower-than-required speed limits may make most drivers non-compliant, whereas higher-than-required speed limits may increase the number of crashes together with related injuries and fatalities. In 2011, the speed limit on a number of freeway segments in the state of Kansas increased from 70 to 75 miles per hour. The objective of this study is to evaluate the safety effects of freeway sections affected by speed limit change in Kansas. Sections where the speed limit changed from 70 mph to 75 mph and other comparable sections where the speed limit remained at 70 mph without any change were identified. Details of the crashes by severity level for 3 years before (2008–2010) and 3 years after (2012–2014) the speed limit change were collected using the state crash database. In order to get a general understanding, characteristics of crashes such as nighttime versus daytime, number of trucks involved, weather conditions, driver's gender, and other such factors were considered. Furthermore, several crash contributory causes were also investigated before and after the speed limit change. In order to evaluate the safety situation, three methods were utilized: (1) Empirical Bayes (EB) observational before-and-after studies; (2) Before-and-after method with comparison group; and (3) Cross-sectional method using the Negative Binomial (NB) regression model. The evaluation was conducted to see if the speed limit change has caused an increase in total crashes or fatal and injury crashes. In regard to speed analysis, the t-test was applied to see whether significant increases in the 85th percentile speed were observed between before-and-after conditions. Since the sample size was large, the Kolmogorov-Smirnov (K-S) test was also conducted to see if there was any difference between two sets of speed data distributions in the before period compared to the after period. By performing the EB before-and-after study, it was seen that total crashes increased by 16 percent, while using the before-and-after method with the comparison group showed around 27 percent increase in total crashes. Total crash increases were statistically significant according to the EB method, and the before-and-after method with the comparison group. On the other hand, fatal and injury crashes increased by 35 percent based on the before-and-after with the comparison group after the speed limit change. This increase was statistically significant, but the EB method results indicated no significant increase in fatal and injury crashes when the speed limit was raised to 75 mph. Further, cross-sectional study results showed the speed limit increase had a significant effect on total crashes, an increase of 25 percent; it was also significant for fatal and injury crashes, with those increasing by 62 percent, which is the highest amount of increase compared to the EB method and the before-and-after method with the comparison group. By considering pros and cons of each methodology, it can be said that the before-and-after method with comparison group provided the most reliable results. The t-test results showed the 5-mph increase in the speed limit caused a statistically significant increase in 85th percentile speed for the sections affected by speed limit change. However, there was also an increase for the sections without a speed limit change, but this was due to large sample sizes of speed data in the before-and-after period. The K-S test results also showed that the speed distribution of treated sites during the after period was different than the before period. Understanding the results of this study will help with future speed limit adjustments on freeways in Kansas.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In the United States, the mileage of unpaved roads is about 1.6 million miles. Total length of unpaved roads in Kansas is about 98,000 miles, of which about 78,000 miles are gravel roads. Most of the gravel roads are not posted with speed limit signs but regulated with a 55 mph blanket speed limit established by the Kansas Statutes. Surface conditions of gravel roads are very likely to change with time, space, and quality of maintenance work, making it even more necessary to have proper control of speeds on gravel roads. Normally used speed regulations and rules for freeways or other types of paved roadways might not be appropriate for gravel roads, especially for those local gravel roads which usually carry very low traffic in rural areas. Based on an extensive literature search, there was no specific rule or references to provide guidelines on how speed limits on gravel roads could be set. Therefore, an effort was made in this study to evaluate the effects of currently posted lower speed limits in some counties in Kansas, based on traffic characteristics and safety on gravel roads, with the intention of providing proper guidelines for setting speed limits on gravel roads in Kansas. In order to study traffic characteristics on gravel roads, field speed studies were conducted with automatic traffic counters on more than forty gravel road sections in seven counties in Kansas. Important speed measures, such as 85th-percentile speed and mean speed, were obtained from the raw data. A group of other related road characteristics were also recorded at the time of field data collection. Crash data on gravel roads were extracted from the Kansas Accident Recording System (KARS) database. Speed analysis on a number of gravel roads where the statutory imposed, unposted speed limit of 55 mph was utilized indicated that they are functioning at a reasonably acceptable level in terms of actual speeds. In order to evaluate whether there were differences in traffic speeds between two counties or groups which have different speed limit settings on gravel roads, t-test was used. The analysis found that there was no significant difference between the mean speeds in two counties, one of which has 35 mph posted speed limit on gravel roads while the other does not post any speed limits. Moreover, the mean speed on the sections with 35 mph posted speed was a little higher than that on gravel roads without any speed limits. Linear models to predict 85th-percentile speed and mean speed on gravel roads were developed based on speed data. Both models indicated that traffic speeds are not significantly affected by the speed limit, but are related with 90% confidence to road width, surface classification and percentage of large vehicles in traffic. Chi-square tests were conducted with the crash data, and the results indicated that the posted 35 mph speed limit on gravel roads had not resulted in either smaller total number of crashes or decreased proportion of severe crashes, compared to gravel roads where no speed limits were posted. Logistic regression models were also developed on four levels of crash severity, which indicated that gravel roads with higher speed limits are likely to experience higher probability of having injury crashes. Two mail-back surveys were also conducted to gather the opinions of county engineers and road users on the subject of suitable speed limits on gravel roads. The majority of county engineers believed that blanket speed limit should be used for gravel roads and does not need to be posted. Three restrictions: changeful road conditions, unpractical law enforcement, and limited funds, are basic reasons why they do not think that gravel roads should be posted. Besides that, a few respondents said 55 mph is too high for gravel roads and needs to be lowered. Majority of the road users suggested that all gravel roads be posted with lower speed limit signs. However, they were more concerned about law enforcement since they believe that posted speeds won't bring any benefits if no law enforcement patrol gravel roads. Based on all aspects looked into in this study, it does not appear that reducing the speed limits and posting it with signs, is going to improve either traffic operational or safety characteristics on gravel roads in Kansas, and therefore is not recommended for new situations.
Author: United States. Congress. House. Committee on Public Works and Transportation. Subcommittee on Surface Transportation Publisher: ISBN: Category : Speed limits Languages : en Pages : 878
Author: Publisher: Transportation Research Board ISBN: 9780309065023 Category : Business & Economics Languages : en Pages : 444
Book Description
TRB Special Report 254 - Managing Speed: Review of Current Practices for Setting and Enforcing Speed Limits reviews practices for setting and enforcing speed limits on all types of roads and provides guidance to state and local governments on appropriate methods of setting speed limits and related enforcement strategies. Following an executive summary, the report is presented in six chapters and five appendices.
Author: Sunanda Dissanayake Publisher: ISBN: Category : Gravel roads Languages : en Pages : 150
Book Description
"In the United States, there are nearly 1.6 million miles of unpaved roads. Total length of unpaved roads in Kansas is about 98,000 miles, of which about 78,000 miles are gravel roads. Most of the gravel roads are not typically posted with speed limit signs but rather are regulated with a 55 mph blanket speed limit established by Kansas statutes. Surface conditions of gravel roads are likely to change with time, space, and quality of maintenance work, making it even more necessary to have proper control of traffic speeds on these roads. Normally used speed regulations and rules for freeways or other types of paved roadways might not be appropriate for gravel roads, especially for those local thoroughfares which usually carry very low traffic in rural areas. An extensive literature search revealed no specific rules or references to provide guidelines on setting speed limits on gravel roads. Therefore, an effort was made in this study to evaluate the effects of currently posted lower speed limits in some Kansas counties based on traffic characteristics and safety on gravel roads, with the intention of providing proper guidelines for setting speed limits on gravel roads in Kansas. Speed analysis on a number of gravel roads where the statutory-imposed, frequently unposted speed limit of 55 mph was utilized indicated that they are functioning at a reasonably acceptable level in terms of actual speeds. In order to evaluate whether there were differences in traffic speeds between two counties or groups which have different speed limit settings on gravel roads, a t-test was used. The analysis found no significant difference between mean speeds in two counties, one of which has a 35 mph posted speed limit on gravel roads while the other did not post any speed limits. Moreover, mean speed on sections with a 35 mph posted speed was a little higher than on gravel roads without any speed limits. Linear models to predict 85th-percentile speed and mean speed on gravel roads were developed based on speed data. Both models indicated that traffic speeds are not significantly affected by the speed limit, but are related with 90% confidence to road width, surface classification, and percentage of large vehicles in traffic. Chi-square tests were conducted with crash data, and the results indicated that the posted 35 mph speed limit on gravel roads had not resulted in either smaller total number of crashes or decreased proportion of severe crashes, compared to gravel roads where no speed limits were posted. Logistic regression models were also developed on four levels of crash severity, which indicated that gravel roads with higher speed limits are likely to experience a higher probability of injury crashes. However, special sections such as curves and bridges were also included in the dataset considered in this analysis, making it impossible to make a direct comparison with the other sections."--Technical report documentation page.
Author: Kara Kockelman Publisher: ISBN: Category : Roads Languages : en Pages : 16
Book Description
TRB's National Cooperative Highway Research Program (NCHRP) Research Results Digest 303: Safety Impacts and Other Implications of Raised Speed Limits on High-Speed Roads explores the effects of raised speed limits from 55 miles per hour or greater on freeways and non-freeways in rural and urban settings. The effects considered included impacts on safety and operations, as well as socioeconomic and environmental effects. The full report is available on the TRB website as NCHRP Web-Only Document 90.
Author: Yacoub M. Najjar
Author: 
Author: United States. National Highway Traffic Safety Administration
Author: Sunanda Dissanayake
Author: 
Author: United States. Congress. House. Committee on Public Works and Transportation. Subcommittee on Surface Transportation
Author: 
Author: Sunanda Dissanayake
Author: 
Author: Kara Kockelman