scholarly journals Evaluating the Safety Impacts of Increased Speed Limits on Freeways in Kansas Using Before-And-After Study Approach

2018 ◽  
Vol 11 (1) ◽  
pp. 119 ◽  
Author(s):  
Reza Shirazinejad ◽  
Sunanda Dissanayake ◽  
Ahmed Al-Bayati ◽  
David York
Keyword(s):  
Traffic Safety ◽  
Economic Benefits ◽  
Group Method ◽  
Speed Limit ◽  
Speed Limits ◽  
Study Approach ◽  
Highway Safety Manual ◽  
Before And After ◽  
Crash Modification Factors ◽  
Before And After Study

In the summer of 2011, a change in the Kansas laws came into effect, increasing the speed limit on a selected set of freeway sections from 70 mph to 75 mph. Higher speeds were thought to have economic benefits, mostly because the travel time reduction means people reach their destinations more quickly. In this study, the sections where the speed limits remained unchanged, are compared to freeway sections that have been influenced by speed limit increase, to evaluate safety effectiveness. The study utilizes the before-and-after study with comparison group method to assess the safety effects provided in the Highway Safety Manual (HSM). Two crash datasets, obtained by considering three years before and three years after the speed limit increase, were compared in order to evaluate the safety effects of the speed limit change. The crash modification factors (CMFs) were estimated, which showed that there was a 27% increase in total crashes and a 35% increase in fatal and injury crashes across all sections after the speed limit change, and these increases were statistically significant at 95% confidence level. These confounding results show that the speed limit increase has not been beneficial for traffic safety in Kansas, and hence it is important to be cautious in such future situations. Also, additional data have been presented which would be beneficial in identifying and understanding any behavior change in drivers following a speed limit increase.

scholarly journals Effects of higher maximum speed limits to vehicle speeds: A before - after analysis on rural divided highways in Vietnam

2018 ◽  
Vol 12 (3) ◽  
pp. 132-137
Author(s):  
Do Duy Dinh ◽  
Thai Hong Nam ◽  
Vu Hoai Nam
Keyword(s):  
Traffic Safety ◽  
Maximum Speed ◽  
P Value ◽  
Speed Limit ◽  
Speed Limits ◽  
Wide Range ◽  
Before And After ◽  
Speed Management ◽  
The Mean ◽  
Very High

This study is to assess the effects of raising speed limits to vehicle operating speeds on rural divided highways in Vietnam. Vehicle speeds were recorded at three different sites of three routes during the daytime and nighttime, both before and after speed limits on these sites increasing from 80 km/h to 90 km/h. The results have shown that the percentage of speeds exceeding speed limits had a wide range from 0% to nearly 30% with regard to different locations, survey time and speed limits. The extent of speeding in some cases was very high even after speed limit increased. It was found that in most cases, the changes in mean speeds after a higher speed limit was applied were statistically significant at the p-value of 0.05, however, the magnitudes of the mean change varied considerably between locations and survey times. Because four out of six cases under the study having mean speeds increased by over 10 km/h after setting up a higher speed limit, this study suggests that further appropriate measures of speed control and speed management should be applied along with increasing speed limit to ensure traffic safety on rural divided highways in Vietnam. Article history: Received 27 March 2018, Revised 18 April 2018, Accepted 27 April 2018

Lowering the speed limit from 30 mph to 25 mph in Boston: effects on vehicle speeds

2019 ◽  
Vol 26 (2) ◽  
pp. 99-102 ◽  
Author(s):  
Wen Hu ◽  
Jessica B Cicchino
Keyword(s):  
Rhode Island ◽  
Local Communities ◽  
Speed Limit ◽  
Speed Limits ◽  
State Laws ◽  
Logistic Regression Models ◽  
Road Users ◽  
Before And After ◽  
Flow Speeds ◽  
Log Linear

IntroductionEffective 9 January 2017, the default speed limit on Boston streets was reduced from 30 mph to 25 mph. This study evaluated the effects of the speed limit reduction on speeds in Boston.MethodVehicle speeds were collected at sites in Boston where the speed limit was lowered, and at control sites in Providence, Rhode Island, where the speed limit remained unchanged, before and after the speed limit change in Boston. A log-linear regression model estimated the change in vehicle speeds associated with the speed limit reduction. Separate logistic regression models estimated changes in the odds of vehicles exceeding 25 mph, 30 mph and 35 mph associated with the lower speed limit.ResultsThe speed limit reduction was associated with a 0.3 % reduction in mean speeds (p=0.065), and reductions of 2.9%, 8.5% and 29.3 % in the odds of vehicles exceeding 25 mph, 30 mph and 35 mph, respectively. All these reductions were statistically significant.ConclusionsLocal communities should consider lowering speed limits to reduce speeds and improve safety for all road users. The current practice of setting speed limits according to the 85th percentile free-flow speeds, without consideration of other characteristics of the roadway, can be a hurdle for local communities looking to lower speed limits. Updated state laws that allow municipalities to set lower speed limits on urban streets without requiring costly engineering studies can provide flexibility to municipalities to set speed limits that are safe for all road users.

Developing Crash Modification Factors for Horizontal Curves on Rural Two-Lane Undivided Highways Using a Cross-Sectional Study

2017 ◽  
Vol 2636 (1) ◽  
pp. 53-61 ◽  
Author(s):  
Lingtao Wu ◽  
Dominique Lord ◽  
Srinivas Reddy Geedipally
Keyword(s):  
Regression Models ◽  
Cross Sectional Study ◽  
Highway Safety ◽  
Sectional Study ◽  
Cross Sectional ◽  
Highway Safety Manual ◽  
Horizontal Curves ◽  
Before And After ◽  
Crash Modification Factors ◽  
Curve Radius

Horizontal curves have been identified as experiencing more crashes than tangent sections on roadways, especially on rural two-lane highways. The first edition of the Highway Safety Manual provides crash modification functions (CM functions) for curves on rural two-lane highways. The CM functions proposed in the manual may suffer from both outdated data and analysis technique. Before-and-after studies are usually the preferred method for estimating the safety effects of treatments. Unfortunately, this method is not feasible for curves. Previous studies have frequently used regression models for developing CM functions for horizontal curves. As recently documented in the literature, some potential problems exist with using regression models to develop crash modification factors. This research utilized a cross-sectional study to develop curvature CM functions. Curves located on Texas rural two-lane undivided highways were divided into a number of bins based on the curve radius. Safety was predicted with the assumption that these curves had been tangents. The observed number of crashes that occurred on the curves was compared with the dummy tangents and for different bins. The results showed that the horizontal curve radius has a significant role in the risk of a crash. From these results, a new CM function was developed. The prediction performance of the Highway Safety Manual CM function was compared with the new CM function in this study and another function that was recently proposed in the literature. It was found that the new CM function documented in this study outperformed both.

Evaluation of Speed Limits in Kentucky

1998 ◽  
Vol 1640 (1) ◽  
pp. 57-64 ◽  
Author(s):  
Kenneth R. Agent ◽  
Jerry G. Pigman ◽  
Joel M. Weber
Keyword(s):  
Speed Limit ◽  
Review Of Literature ◽  
Speed Limits ◽  
Fatal Accident ◽  
Engineering Study ◽  
Before And After ◽  
Accident Data ◽  
Accident Rates ◽  
Specific Section ◽  
Moving Speed

The objectives were to examine current criteria and procedures used for setting speed limits and to determine appropriate speed limits for various types of roads. The study involved a review of literature, collection and analysis of speed data, and collection and analysis of accident data. The speed data included moving speed data on various highway types and a comparison of speed data before and after speed limit changes. Accident data were collected at locations where speed limits were changed and also on sections of adjacent Interstates with different speed limits. The speed data indicate that a large percentage of vehicle speeds exceed posted speed limits, with the highest percentage being on urban Interstates and two-lane parkways. The speeds for trucks were slightly lower than for cars. A comparison of speed data at locations where speed limits were changed showed only slight differences. A comparison of accident rates at adjacent sections of Interstate where the speed limit was 88.6 km/hr (55 mph) and 104.7 km/hr (65 mph) did not find a substantial difference in the total, injury, or fatal accident rates. Except where legislatively mandated speed limits apply, the 85th-percentile speed should be used to establish speed limits. Maximum limits are given for various types of roadways. Different speed limits for cars and trucks are recommended for some roadways. An engineering study must be conducted before the speed limit should be changed for any specific section of roadway.

Development of Crash Reduction Factors: Methods, Problems, and Research Needs

2003 ◽  
Vol 1840 (1) ◽  
pp. 50-56 ◽  
Author(s):  
Joan Shen ◽  
Albert Gan
Keyword(s):  
Empirical Bayes ◽  
Group Method ◽  
Research Needs ◽  
Regression To The Mean ◽  
Before And After ◽  
Safety Studies ◽  
Development Methods ◽  
Crash Reduction ◽  
Before And After Study ◽  
Reduction Factors

Crash reduction factors (CRFs) are used in highway safety studies to predict safety benefits due to reduced numbers of crashes. NCHRP Report 162 identified the need for the development of a national comprehensive set of CRFs for each state to evaluate safety improvements. However, this need has not been met. As a result, many states have developed their own CRFs or have adopted CRFs from other states. A synthesis of the CRF development methods, the associated problems, and the research needs are provided. The emphasis is placed on the before-and-after study method because it has been, and still is, the method of choice for CRF development. Three before-and-after study methods were introduced and reviewed: ( a) the simple before-and-after method, ( b) the before-and-after study with comparison group method, and ( c) the before-and-after study with the empirical Bayes method. The problems associated with the simple before-and-after studies, including regression to the mean, crash migration, maturation, and external causal factor, are discussed. Several research needs related to crash migration and general CRF development are also identified. The information presented in the synthesis will be useful to states that plan to develop or update their CRFs.

scholarly journals Evaluation of Speeding and Behaviour of Drivers in Roadwork Zones

2018 ◽  
Vol 13 (3) ◽  
Author(s):  
Donatas Čygas ◽  
Dovydas Skrodenis ◽  
Aivaras Paškauskas ◽  
Živilė Sušinskaitė ◽  
Laura Žalimienė
Keyword(s):  
Traffic Flow ◽  
Traffic Safety ◽  
European Countries ◽  
Significant Problem ◽  
Speed Limit ◽  
Work Zones ◽  
Speed Limits ◽  
Safety Measures ◽  
Speed Measurement ◽  
Road Work

Due to the increased traffic flow, more and more roadwork zones are formed in highways. Accidents are a significant problem in all European countries in roadwork zones while noncompliance with speed limits is one of the major safety concerns. Therefore roadwork zones are critical places from the point of traffic safety view where the possibility to get into an accident is increased. Roadwork zones introduce deviations from regular travel situations, and appropriate speed is needed to assure that the driver navigates safely through the roadwork zone. This research focuses on speed measurement in road work zones and attempts to evaluate the effectiveness of safety measures on speed limit compliance.

scholarly journals Speed Characteristics in Relation to Speed Limit Increase and Its Influence on Driver’s Speed Selection Behavior

2020 ◽  
Vol 12 (4) ◽  
pp. 1369
Author(s):  
Reza S. Shirazinejad ◽  
Sunanda Dissanayake
Keyword(s):  
Traffic Safety ◽  
Quality Measurement ◽  
Speed Limit ◽  
Test Results ◽  
Significant Difference ◽  
Selection Behavior ◽  
Before And After ◽  
Kolmogorov Smirnov ◽  
Speed Selection ◽  
And Control

Speed is a quality measurement for travel, since it is related to traffic, safety, time, and economics. The speed limit on selected freeways in Kansas changed from 70 mph to 75 mph in the summer of 2011. In this study, the driver’s speed selection behavior was analyzed by considering average speed and 85th percentile speed in the before and after periods. Data from Automatic Traffic Recorders (ATRs) on the sections affected by speed limit increase and sections with no speed limit increase were analyzed. The t-test was applied to investigate if there was any significant difference in the speed of drivers on both treated and control sections. The Kolmogorov-Smirnov (K-S) test was also conducted to see if the distribution of speed data in the before period was different than after the period. The results showed that for the majority of the sections affected by speed limit change, there was a statistically significant difference in the 85th percentile speed of drivers during after period. Additionally, the K-S test results showed that the distribution of speed data in the before period was different than after the period for the majority of treated sections. The results indicated how drivers’ behavior was influenced by the speed limit increase.

scholarly journals Exploring the Impact of Differentiated Per-Lane Speed Limits on Traffic Safety of Freeways with Considering the Compliance Rate

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Meiyu Liu ◽  
Jing Shi
Keyword(s):  
Cellular Automata ◽  
Traffic Safety ◽  
Coefficient Of Variation ◽  
Compliance Rate ◽  
Speed Limit ◽  
Speed Limits ◽  
Lane Changing ◽  
Incident Rate ◽  
The Right ◽  
The Impact

This is a subsequent study of a two-lane cellular automata (CA) traffic simulation model proposed by the authors. The current study focused on understanding the impacts of the configuration of the differentiated per-lane speed limit (DPLSL) and its compliance rate on traffic safety indexes, including lane-changing frequency, the coefficient of variation of speed, and incident rate of dangerous situations. The results indicate that freeway sections with DPLSL, especially the ones with complex DPLSL, have potentials to reduce the speed variation, lane changing frequencies, and chances of dangerous situations, resulting in higher traffic safety levels. Furthermore, under DPLSL configurations, the compliance rate of the lane of slow vehicles could positively affect the traffic safety levels. Specifically, as the decrease of the compliance rate, lane changing frequency slightly increases, the coefficient variation of speed especially of the outer lane increases, and the incident rate of the overtaking-on-the-right circumstances increases. In contrast to the simple DPLSL, freeway segments with the complex DPLSL configuration are more sensitive to the influence of the compliance rate.

Analysis of Rural Interstate Fatality Rates in Consideration of Recent Increases in Maximum Statutory Speed Limits

2019 ◽  
Vol 2673 (11) ◽  
pp. 48-58
Author(s):  
Jacob Warner ◽  
Hitesh Chawla ◽  
Chao Zhou ◽  
Peter T. Savolainen
Keyword(s):  
Traffic Safety ◽  
Negative Binomial ◽  
Unobserved Heterogeneity ◽  
State Level ◽  
Random Parameter ◽  
Maximum Speed ◽  
Speed Limit ◽  
Speed Limits ◽  
Fatal Crashes ◽  
Significant Research

The relationship between traffic safety and speed limits has been an area of significant research. Since the repeal of the National Maximum Speed Law in 1995, states have full autonomy in establishing maximum statutory speed limits. Since 2001, at least 25 states have increased their maximum limits to speeds as high as 85 mph. This study examines changes in rural interstate fatalities from 2001 to 2016 in consideration of such increases. Speed limit policy data include the maximum speed limit for each state–year combination, as well as the proportion of rural interstate mileage posted at each speed limit in each state. Random parameter negative binomial models are estimated to control for unobserved heterogeneity, as well as time-invariant effects unique to each state. The results show that increasing the mileage of rural interstates posted at 70, 75, or 80 mph by 1% is associated with fatality increases of 0.2%, 0.5%, and 0.6%, respectively. These increases are more pronounced than when considering only the maximum statutory limits in each state. The study also examines the influence between these higher limits and the frequency of fatal crashes involving speeding and driver distraction. At the highest limits of 75 and 80 mph, the increases among these subsets of crashes are greater than the increases in total fatalities. Ultimately, this study provides important empirical evidence in support of continuing speed limit policy discussions, in addition to identifying salient analytical concerns that should be considered as a part of longitudinal analyses of state-level fatality data.

scholarly journals Estimation of Optimal Speed Limits for Urban Roads Using Traffic Information Big Data

2021 ◽  
Vol 11 (12) ◽  
pp. 5710
Author(s):  
Hyungkyu Kim ◽  
Doyoung Jung
Keyword(s):  
Traffic Safety ◽  
Safety Information ◽  
Traffic Information ◽  
Maximum Speed ◽  
Speed Limit ◽  
Speed Limits ◽  
The Road ◽  
Optimal Speed ◽  
Road Users ◽  
Adjustment Factors

The use of an inconsistent speed limit determination method can cause low speed limit compliance. Therefore, we developed an objective methodology based on engineering judgment considering the traffic accident rate in road sections, the degree of roadside development, and the geometric characteristics of road sections in urban roads. The scope of this study is one-way roads with two or more lanes in cities, and appropriate sections were selected among all roads in Seoul. These roads have speed limits of the statutory maximum speed of 80 km/h or lower and are characterized by various speeds according to the function of the road, the roadside development, and traffic conditions. The optimal speed limits of urban roads were estimated by applying the characteristics of variables as adjustment factors based on the statutory maximum speed limit. As a result of investigating and testing various influence variables, the function of roads, the existence of median, the level of curbside parking, the number of roadside access points, and the number of traffic breaks were selected as optional variables that influence the operating speed. The speed limit of one-way roads with two or more lanes in Seoul was approximately 10 km/h lower than the current speed limit. The existing speed limits of the roads were applied uniformly considering only the functional road class. However, considering the road environment, the speed limit should be applied differently for each road. In the future, if the collection scope and real-time collection of road environment information can be determined, the GIS visualization of traffic safety information will be possible for all road sections and the safety of road users can be ensured.

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