Safety Evaluation of Change in Posted Speed Limit from 65 to 70 mph on Rural Virginia Interstate System

2018 ◽  
Vol 2672 (38) ◽  
pp. 35-45
Author(s):  
Scott Himes ◽  
Frank Gross ◽  
Michael Nichols ◽  
Mena Lockwood
Keyword(s):  
Empirical Bayes ◽  
Safety Evaluation ◽  
Speed Limit ◽  
Department Of Transportation ◽  
Run Off ◽  
Adjustment Factors ◽  
Interstate System ◽  
Virginia Department ◽  
Crash Types ◽  
Disaggregate Analysis

Effective July 1, 2010, the Virginia Department of Transportation (VDOT) increased the maximum posted speed limit on interstates and similar facilities from 65 to 70 mph, if recommended following an engineering study. As a result, VDOT performed engineering studies on selected rural interstates posted at 65 mph. By November 2010, VDOT had increased the speed limit from 65 to 70 mph for approximately 670 centerline miles of select rural interstates. This paper presents the results of an empirical Bayes before–after study into the safety and operational effects of the speed limit increase. The analysis focused on total, injury, run-off-road, and truck-related crashes. Comparison segments were used to develop annual adjustment factors, account for regional differences, and identify underlying crash trends in the period before the speed limit increase. At the aggregate level, the results indicated no increase in any of the focus crash types after the increase. Focusing on sites without other changes, the increased speed limit did not increase or decrease any of the crash types. The disaggregate analysis provided further insight into the circumstances in which the change in posted speed limit had more and less pronounced impacts; specifically, that segment type (base or interchange) influenced safety: interchange segments observed statistically significant increases in total, run-off-road, and truck-related crashes. The disaggregate analysis also showed that roadway improvements may help to offset the safety impact of increasing the posted speed limit.

Evaluating the Safety Effects of Span Wire to Mast Arm Signal Conversion

2018 ◽  
Vol 2672 (30) ◽  
pp. 21-31 ◽  
Author(s):  
Zulqarnain H. Khattak ◽  
Michael D. Fontaine
Keyword(s):  
Road Safety ◽  
Empirical Bayes ◽  
Comprehensive Evaluation ◽  
Department Of Transportation ◽  
Crash Data ◽  
Signal Conversion ◽  
Modification Factor ◽  
Virginia Department ◽  
Crash Types ◽  
Safety Benefit

The mast arm signal mounting configuration has often been assumed to provide greater conspicuity and visibility than span wire installations, but the impacts of this countermeasure on road safety have not been well established quantitatively. This paper’s intent is to provide a comprehensive evaluation of safety effects of converting span wire installations to mast arm installations. An Empirical Bayes before–after safety analysis was conducted using crash data for 30 intersections collected from the Virginia Department of Transportation (VDOT). A crash type analysis was also conducted to observe changes in crash types. Based on the data available, no statistically significant improvement in safety was found. Average crash modification factor (CMF) values of 0.97 and 0.98 were observed for total and fatal and injury crashes, but these CMFs were not statistically significant. A reduction in the proportion of angle crashes was observed, but the change was not statistically significant and the overall distribution of crashes did not change significantly after converting signal configurations from span wire to mast arm. Although mast arm deployments may offer advantages in maintenance costs and aesthetics, there does not appear to be a substantial safety benefit to these conversions.

Empirical Bayes Before-After Study to Develop Crash Modification Factors and Functions for High Friction Surface Treatments on Curves and Ramps

2020 ◽  
Vol 2674 (12) ◽  
pp. 505-514 ◽  
Author(s):  
Craig Lyon ◽  
Bhagwant Persaud ◽  
David Merritt ◽  
Joseph Cheung
Keyword(s):  
Friction Surface ◽  
Empirical Bayes ◽  
Crash Frequency ◽  
Run Off ◽  
Innovative Methodology ◽  
Crash Modification Factors ◽  
Using Data ◽  
Benefit Cost ◽  
Crash Types ◽  
Disaggregate Analysis

The intent of the study was to fill a knowledge void by developing high quality crash modification factors (CMFs) and benefit/cost (B/C) ratios for high friction surface treatment (HFST). The state-of-the-art empirical Bayes (EB) before-after methodology was applied to evaluate the effects of this treatment on crashes of various types using data from West Virginia (curve sites), Pennsylvania (curve sites), Kentucky (curve and ramp sites), and Arkansas (ramp sites). The results for curve sites generally indicate substantial and highly significant safety benefits. This is especially so for the primary crash types targeted by HFST programs: run-off-road, wet road, and head-on side-swipe opposite direction crashes (HOSSOD). The results for ramp sites were inconsistent, with substantial benefits for all crashes and injury crashes for Kentucky, negligible effects for these crashes in Arkansas, and substantial and highly significant reductions in wet weather crashes in both states. A disaggregate analysis of the CMF results for curve sites indicated a logical and consistent relationship between CMFs and three variables: friction improvement, traffic volume, and expected crash frequency before treatment. These variables, and an innovative methodology, were used in developing crash modification functions (CMFunctions) that can be applied to determine where, and under what conditions, the treatment can be used most effectively. Such functions are typically not provided for the vast majority of treatments for which CMFs are available, so, in itself, developing them is a significant contribution of this research.

Safety Evaluation of Alternative Audible Lane Departure Warning Treatments in Reducing Traffic Crashes: An Empirical Bayes Observational Before–After Study

2018 ◽  
Vol 2672 (21) ◽  
pp. 30-40 ◽  
Author(s):  
Lingtao Wu ◽  
Srinivas R. Geedipally ◽  
Adam M. Pike
Keyword(s):  
Empirical Bayes ◽  
Safety Evaluation ◽  
Highway Safety ◽  
Warning Systems ◽  
Lane Departure Warning ◽  
Crash Data ◽  
Pavement Markings ◽  
Lane Departure ◽  
Run Off ◽  
Single Vehicle

Roadway departure crashes are a major contributor to traffic fatalities and injury. Rumble strips have been shown to be an effective countermeasure in reducing roadway departure crashes. However, some roadway situations, for instance, inadequate shoulder width or roadway surface depth, have limited the application of conventional milled or rolled in rumble strips. Alternative audible lane departure warning systems, including profile (audible) pavement markings and preformed rumble bars, are increasingly used to overcome the limitations that exist with the milled rumble strips. So far, the safety effectiveness of these alternative audible lane departure warning systems has not been extensively assessed. The main purpose of this paper is to examine the safety effect of installing profile pavement markings and preformed rumble bars. Specifically, this study developed crash modification factors for these treatments that quantify the effectiveness in reducing single-vehicle-run-off-road (SVROR) and opposite-direction (OD) crashes. Traffic, roadway, and crash data at the treated sites on 189 miles of rural two-lane highways in Texas were analyzed using an empirical Bayes (EB) before–after analysis method. Safety performance functions from the Highway Safety Manual and Texas Highway Safety Design Workbook were used in the EB analysis. The results revealed a 21.3% reduction in all SVROR and OD crashes, and 32.5% to 39.9% reduction in fatal and injury SVROR and OD crashes after installing profile pavement marking and preformed rumble bars.

scholarly journals Safety evaluation of roundabouts at freeway ramp terminals and HSM calibration

2017 ◽  
Author(s):  
◽  
Jacob A. Berry
Keyword(s):  
Empirical Bayes ◽  
Safety Evaluation ◽  
Crash Severity ◽  
Site Specific ◽  
Crash Data ◽  
Highway Safety Manual ◽  
Time Period ◽  
Using Data ◽  
Crash Types ◽  
Project Level

Although the conventional understanding is that roundabouts have the potential to improve safety at intersections, particularly by reducing more severe crash types, there is limited knowledge on their safety impacts when utilized as part of an interchange system. This research utilizes multiple years of crash, traffic, and geometric data across a variety of roundabout interchange sites in Missouri to develop a two-level Empirical Bayes (EB) safety analysis at the project (entire interchange) and site-specific (ramp terminal only) levels. The results were then aggregated for both single-lane and dual-lane roundabout terminals. The project-level results for single-lane sites showed a decrease in fatal/injury crashes (FI) by 20.3 percent, property damage only (PDO) crashes by 26.0 percent and total crashes by 24.5 percent. The site-specific results for single-lane roundabout terminals indicated a reduction of FI crashes by 32.8 percent, PDO crashes by 23.1 percent, and total crashes by 24.4 percent. At the project-level, dual-lane roundabouts were shown to reduce FI crashes by 2.3 percent while increasing PDO and total crashes by 16.9 percent and 12.2 percent, respectively. The dual-lane site-specific results indicated an increase in FI crashes by 34.7 percent, PDO crashes by 53.9 percent, and total crashes by 50.0 percent at the ramp terminal specifically. This analysis directly compares observed crash data after roundabout implementation to the expected number of crashes over that time period if the roundabout were never constructed. Therefore, this indicates that single-lane roundabouts performed significantly better than their original configurations, while the dual-lane roundabout terminals were shown to be less-suitable for certain applications. Additionally, it was found that a high proportion of the roundabout crashes occurred at the exit ramp approach legs; this was illustrated in the collision diagrams and crash type distributions that were produced for the common observed crashes at both single and dual-lane roundabout terminals. As a separate part of this thesis research, an improved calibration of the Highway Safety Manual safety performance functions of four facility types was performed using data from 2012-2014 to calibrate for local Missouri conditions. Crash severity and crash type distributions were also developed for each facility type.

Safety Evaluation of the SafetyEdge Treatment for Pavement Edge Drop-Offs on Two-Lane Rural Roads

2018 ◽  
Vol 2672 (30) ◽  
pp. 1-8
Author(s):  
Craig Lyon ◽  
Bhagwant Persaud ◽  
Eric Donnell
Keyword(s):  
Empirical Bayes ◽  
Safety Evaluation ◽  
Cost Effective ◽  
Rural Highways ◽  
The Road ◽  
Run Off ◽  
Lane Width ◽  
Traffic Volumes ◽  
Pre Treatment ◽  
Edge Drop

This study estimated crash modification factors (CMFs) for the SafetyEdge paving technique that is applied for the treatment of pavement edge drop-offs on two-lane rural highways. An empirical Bayes observational before-after evaluation based on installation data in Iowa, North Carolina, Ohio, Pennsylvania, and Florida found that the SafetyEdge treatment was associated with statistically significant reductions in fatal and injury (FI), run-off-the-road (ROR), opposite-direction (head-on and sideswipe), and drop-off-related crashes. The ROR CMF was also statistically significant for both horizontal curved and tangent sections. A disaggregate analysis examined the variation of the CMF for ROR with factors such as the travel lane width, traffic volume, presence of a horizontal curve, posted speed limit, and the pre-treatment ROR crash frequency. The results of that analysis indicated, for example, that the SafetyEdge paving technique appears to have a greater ROR safety benefit on two-lane rural roadway segments with average annual daily traffic volumes greater than 3,000 vehicles per day, relative to roadway segments with lower traffic volumes. A crash modification function (CMFunction) was calibrated with expected pre-treatment ROR crashes as the independent variable to simultaneously capture the relationship of the CMF for ROR crashes to multiple factors. An economic analysis found that the treatment is highly cost-effective.

Bridge Substructure Repairs with Self-Consolidating Concrete and Galvanic Anodes

2018 ◽  
Vol 2672 (27) ◽  
pp. 56-64
Author(s):  
H. Celik Ozyildirim ◽  
Stephen R. Sharp
Keyword(s):  
Chloride Content ◽  
Visual Observation ◽  
Department Of Transportation ◽  
Corrosion Activity ◽  
Self Consolidating Concrete ◽  
Reinforced Concrete Bridge ◽  
Form Pressure ◽  
Virginia Department ◽  
Narrow Area ◽  
Chloride Contaminated

Historically, the Virginia Department of Transportation (VDOT) has repaired chloride-contaminated reinforced concrete bridge substructure elements that contain vertical and overhead sections with either shotcrete or a conventional A3 (3,000 psi) or A4 (4,000 psi) concrete. This study investigated using self-consolidating concrete (SCC), which has a high flow rate, bonds well, has low permeability, and provides smooth surfaces, as another option. The study also explored the use of galvanic anodes to control corrosion activity in SCC repairs. In VDOT’s Lynchburg and Staunton Districts, SCC repairs were made with and without the use of galvanic anodes. This provided a means for determining the benefit of using the anodes. The needed repair areas were determined by visual observation and sounding. After 7 years of service, SCC repair areas with and without anodes did not exhibit corrosion activity; small vertical cracks were evident in the SCC but did not affect performance. The anodes can provide protection to the steel immediately adjacent to the repair areas. However, unrepaired concrete areas away from the patched area with anodes now require additional repairs. SCC can be successfully placed; however, attention should be paid to form pressure and slump loss. Selection of repair areas should be based on corrosion-related measurements such as half-cell or chloride content, rather than sounding. Progression of corrosion demonstrates the necessity of removing all chloride-contaminated concrete not just adjacent to, but also away from the reinforcement, as anodes in the repair area will provide protection only in a narrow area around the patch.

Performance of Virginia’s Early Foamed Warm Mix Asphalt Mixtures

2018 ◽  
Vol 2672 (28) ◽  
pp. 178-189 ◽  
Author(s):  
Stacey D. Diefenderfer
Keyword(s):  
Dynamic Modulus ◽  
Permanent Deformation ◽  
Warm Mix Asphalt ◽  
Department Of Transportation ◽  
High Dynamic ◽  
Repeated Load ◽  
And Performance ◽  
Virginia Department ◽  
Performance Grading ◽  
Air Void

The Virginia Department of Transportation began allowing the use of warm mix asphalt (WMA) in 2008. Although several WMA technologies were investigated prior to implementation, foamed WMA was not. This study evaluated the properties and performance of foamed WMA placed during the initial implementation of the technology to determine whether the technology had performed as expected. Six mixtures produced using plant foaming technologies and placed between 2008 and 2010 were identified and subjected to field coring and laboratory testing. Coring was performed in 2014, resulting in pavement ages from 4 to 6 years. Three comparable hot mix asphalt (HMA) mixtures were cored at 5 years for comparison. Cores were evaluated for air-void contents and permeability and were subjected to dynamic modulus, repeated load permanent deformation, and overlay testing. In addition, binder was extracted and recovered for performance grading. Similar properties were found for the WMA and HMA mixtures. One WMA mixture had high dynamic modulus and binder stiffness, but overlay testing did not indicate any tendency for premature cracking. All binders had aged between two and three performance grades above that specified at construction. WMA binders and one HMA binder aged two grades higher, and the remaining two HMA binders aged three grades higher, indicating a likely influence on aging of the reduced temperatures at which the early foamed mixtures were typically produced. Overall results indicated that foamed WMA and HMA mixtures should be expected to perform similarly.

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