Putting Safety Solutions to The Test
In an FHWA study, researchers evaluated the impacts of various countermeasures on real-world driving on rural roads.
Of the 8.7 million lane-miles of roads in the United States, more than 6 million are rural. Almost 71 percent of the lane-miles of rural roads are owned and operated by local entities, making the sharing of highway safety information with local officials and the public critical to improving safety on rural roads nationwide.
Rural areas face a number of distinct safety challenges. Rural crashes are more likely to involve vehicles traveling at higher speeds than urban crashes. Victims of fatal crashes in rural areas are more likely to be unbelted than their urban counterparts, and it often takes first responders longer to arrive at the scene of a rural crash, leaving victims waiting longer for medical attention. Outdated roadway designs and roadside hazards such as utility poles, sharp-edged pavement dropoffs, and trees close to the roadway also are major contributors to the severity of crashes in rural areas.
According to the latest data from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System (FARS), the fatality rate for rural crashes is statistically higher than that of urban crashes. Specifically, NHTSA reports that from 2010 to 2012, 48,852 people were killed in rural motor vehicle crashes (an average of 16,284 per year), accounting for 54 percent of motor vehicle fatalities that occurred on both urban and rural roads.
To address these challenges, the U.S. Department of Transportation launched the Rural Safety Initiative in 2008 as a comprehensive way to help State and local leaders raise awareness of highway safety issues and implement solutions in rural areas more quickly. As part of this initiative, the Federal Highway Administration launched the Rural Safety Innovation Program in February 2008 as a one-time opportunity for rural communities to compete for project funding to address safety problems. The program encouraged rural communities to develop creative, locally crafted solutions to their roadway safety problems, document their efforts and outcomes, and share the results with other communities across the country.
In August 2008, USDOT awarded $14.7 million to 14 States, 3 counties, and 2 parishes under the Rural Safety Innovation Program. The funds were drawn from the Delta Region Transportation Development Program (the Delta Program) and USDOT’s Intelligent Transportation Systems (ITS) program.
What follows is an assessment of the effectiveness of nine highway safety improvement projects implemented in eight States as part of the Rural Safety Innovation Program under the Delta Program. The Delta Program supports transportation development efforts in Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. Also included is an indepth look at projects from two of those States: Mississippi and Missouri. The assessments help shed light on the types of analysis that are appropriate for evaluating the effectiveness of projects to improve highway safety on rural roads.
Assessing the Effectiveness Of Safety Improvements
Nine transportation agencies implemented safety improvement projects in eight States as part of the Delta Program. In general, the agencies identified high-risk locations such as curves and intersections for safety improvements based on crash data and local knowledge. They then selected and installed countermeasures that they believed would be effective and appropriate for systemic implementation.
FHWA’s research objective was to evaluate the effectiveness of these projects, but doing so depended upon the availability of data and the nature of the projects. The Arkansas State Highway and Transportation Department, for example, installed cable median barriers on various rural sections of several interstate highways to reduce the number and severity of crashes related to crossing over the median. The FHWA researchers could use available crash statistics to evaluate the effectiveness of the project.
“A statistical review of the number of crashes and fatalities or serious injuries that took place in past years revealed that installing cable median barriers is a promising crash countermeasure,” says Mojtaba Mohammadi, a traffic safety engineer at the Arkansas State Highway and Transportation Department. “A decreasing trend was observed in the number of fatalities and severe injuries from 2009 to 2012, the period when crash statistics were examined.”
After an initial assessment of all nine projects, the researchers selected three for detailed quantitative evaluations (Illinois, Louisiana, and Mississippi), and one for a simpler quantitative analysis (Arkansas), because it lacked a sufficient number of treatment sites and mileage. Two projects were more suited to a qualitative, rather than quantitative, analysis (Missouri and Tennessee), focusing on lessons learned by the agencies during implementation. The three remaining projects (two Louisiana parishes and one county in Mississippi) were excluded from the evaluation due to insufficient data or challenges in preparing the data for analysis.
Methodology for the Study
The researchers first contacted the nine State and local highway agencies involved to gain a detailed understanding of each project and discuss implementation of the safety countermeasures. The team also identified specific evaluation opportunities, discussed the availability of data for use in its analyses, and identified key contacts within each agency for data requests.
The next step was to develop an evaluation plan for each project. The researchers planned to evaluate the differences in crash frequency and severity before and after specific countermeasures were installed under the Rural Safety Innovation Program. To estimate the safety effectiveness of these projects objectively, the researchers employed Empirical Bayes statistical method. This method makes use of before and after crash data and safety performance functions to estimate the safety effectiveness of a treatment, accounting for factors that change over time, such as traffic volume and weather. A safety performance function is an equation used to predict the average number of crashes per year at a location as a function of exposure and, in some cases, roadway or intersection characteristics (such as number of lanes, traffic control, and median type).
Countermeasures Evaluated Under the Rural Safety Innovation Program â€“ Project Evaluation
|Agency||Countermeasure||General Site Attributes||Type of Evaluation|
|Arkansas State Highway and Transportation Department||Cable median barrier on an interstate highway||Rural interstate||Simpler quantitative|
|Grant Parish, LA||Striping, rumble strips, raised pavement markers, flashing beacon warning signs, large arrow signs, chevrons, and other warning signsÂ||Rural two-lane roads||Not evaluated|
|Hinds County, MS||Signing, striping, and rumble strips||Rural two-lane roads||Not evaluated|
|Illinois Department of Transportation||Advance curve warning signs, speed plates, chevrons, and raised pavement markings||Horizontal curves on rural two-lane roads||Detailed quantitative|
|Louisiana Department of Transportation and Development||Signing and marking improvements at intersections||Intersections on rural roads||Detailed quantitative|
|Mississippi Department of Transportation||Centerline rumble strips and clear zone restoration||Rural two-lane roads||Detailed quantitative|
|Missouri Department of Transportation||Dynamic message signs on interstate highways||Rural interstates||Qualitative|
|Rapides Parish, LA||Striping, rumble strips, raised pavement markers, flashing beacon warning signs, large arrow signs, chevrons, and other warning signsÂ||Rural two-lane roads||Not evaluated|
|Tennessee Department of Transportation||Signing inventory/assessment system||Rural State highways||Qualitative|
Source: FHWAâ€™s Delta Region Transportation Development Program: Rural Safety Innovation Program Evaluation Final Report.
The researchers obtained data on crashes, traffic volumes, roadway characteristics, and countermeasures from project personnel, electronic databases, aerial mapping tools, and field visits. Using this data, the research team estimated the safety effectiveness of treatments installed under the Rural Safety Innovation Program by applying the following steps:
- Calculated predicted crash frequencies for the treatment sites for the period prior to installation, using existing safety performance functions found in the Highway Safety Manual and the “Safety Analyst” software tools, both of which were developed by the American Association of State Highway and Transportation Officials with the help of the Transportation Research Board and FHWA.
- Combined those figures with observed crashes during the period prior to installation using a weighted average to calculate an expected crash frequency for the treatment sites prior to installation.
- Calculated the expected crash frequency had the treatment not been applied by adjusting the expected crash frequency before installation for differences in duration and traffic volumes between the before and after periods.
- Compared the expected crash frequency had the treatment not been applied to the observed crash frequency after installation to assess the safety effectiveness of the treatment.
For projects that did not lend themselves to a detailed quantitative analysis using the Empirical Bayes method, the researchers either applied a simpler before and after comparison or qualitatively evaluated data from available reports and interviews with project personnel.
“Ideally we would like to have as much high-quality data as possible so we can conduct quantitative safety analyses using approaches like the Empirical Bayes method,” says Monique Evans, who is director of the Office of Safety Research and Development at FHWA’s Turner-Fairbank Highway Research Center. “However, in the absence of ideal data conditions, we can still learn a lot from some quantitative analyses that use limited data and from qualitative assessments.”
The researchers’ qualitative evaluations included analysis of lessons learned from projects in Tennessee and Missouri to develop a sign inventory system and install dynamic message signs and closed-circuit video, respectively. Researchers asked personnel involved in the projects whether the countermeasures improved safety and operations and helped them better manage incidents. They also asked questions about implementation: How did the agencies implement the countermeasures? Did they encounter any challenges?
Overall, many of the projects examined did improve safety on rural highways. Projects implemented by the Mississippi and Missouri departments of transportation highlight these outcomes and serve as examples of the research team’s quantitative and qualitative evaluations.
Mississippi Applies Centerline Rumble Strips
The Mississippi Department of Transportation (MDOT) received funding through the Rural Safety Innovation Program to implement two types of safety improvements along rural State highways. The first was installation of centerline rumble strips. The second was restoration of a clear zone, which included removing roadside objects, regrading side slopes, and installing cable barriers along about 5 miles (8 kilometers) of roadway. These improvements focused on reducing the number and severity of lane departure crashes.
MDOT installed approximately 350 miles (563 kilometers) of centerline rumble strips under the program. Many of the target locations already had shoulder rumble strips that had themselves, in most cases, been installed within 1–2 years of deploying the new centerline rumble strips.
Analysis. Because the project to restore the clear zone covered only a few miles of roadway, the researchers decided to focus their evaluation on the effectiveness of installing the centerline rumble strips. They evaluated locations, referred to as treatment sites, where MDOT had installed centerline rumble strips on routes that also had shoulder rumble strips. In addition, the research team analyzed data for nontreatment sites: stretches of rural two-lane highway that had geometrics and traffic volumes similar to the treatment sites but had no rumble strips of any kind during the entire analysis period.
Statistics Before and After Countermeasures Implemented in Mississippi
|Site No.||Number Of Segments Per Site||Total Site LengthÂ (mi)||Before Period||After Period|
|Number Of Years||Average AADT||Total Crashes*||Fatal And All Injury Crashes||Fatal And Serious Injury Crashes||Number Of Years||Average AADT||Total Crashes||Fatal And All Injury Crashes||Fatal And Serious Injury Crashes|
*Crash types include only single vehicle run-off-road crashes (right or left), sideswipe-opposite direction crashes, and head-on crashes.
Source: FHWA’s Delta Region Transportation Development Program: Rural Safety Innovation Program Evaluation Final Report.
Next the researchers compared data from years prior to the installation of either the shoulder or centerline rumble strips against data from years after the installation of the centerline rumble strips. Crash data were generally available from 2005 to 2012; the team excluded from analysis crashes that occurred during the treatment installation year or years.
The researchers calculated the annual average daily traffic (AADT) for each site and year as the average of the AADTs of the segments within each site-year. The team then averaged these AADTs over the before and after years, respectively, for each site.
Comparing before-and-after crash data from 11 treatment sites and 8 nontreatment sites, along with Safety Analyst’s safety performance functions for rural two-lane roads, the researchers applied the Empirical Bayes method to estimate the safety effectiveness of applying both centerline and shoulder rumble strips in reducing the target collision types. The target types included single vehicle run-off-road crashes (right or left side of the road), sideswipe-opposite direction crashes, and head-on crashes. The researchers performed separate analyses for total crashes, fatal and all injury crashes, and fatal and serious injury crashes.
Safety Effectiveness of Countermeasures in Mississippi
|Crash* Type (Severity)||Number of Treatment Sites||Total Site Length (mi)||Safety Effectiveness (%)||Standard Error Of Treatment Effect (%)||Significance|
|Total||11||80.1||-35.0||10.5||Significant at 95% confidence level|
|Fatal and All Injury||11||80.1||-39.6||12.3||Significant at 95% confidence level|
|Fatal and Serious Injury||11||80.1||12.3||39.4||Not significant at 90% confidence level|
*Crash types include only single vehicle run-off-road crashes (right or left), sideswipe-opposite direction crashes, and head-on crashes.
Source: FHWAâ€™s Delta Region Transportation Development Program: Rural Safety Innovation Program Evaluation Final Report.
Results. The safety effectiveness estimates, which showed a 35-percent reduction in total crashes and a 39.6-percent reduction in fatal and all injury crashes, were statistically significant at a 95-percent confidence level. The estimate for fatal and serious injury crashes, however, showed a 12.3-percent increase that was not statistically significant at a 90-percent confidence level and had a standard error of 39.4 percent. The high standard error of that treatment, which caused a statistically insignificant result for fatal and serious injury crashes, was due to the low number of fatal and serious injury crashes observed at the treatment sites: Only 13 fatal and serious injury crashes occurred in the years prior to the treatment, and 10 fatal and serious injury crashes occurred in the period after treatment.
Conclusions. The dual application of centerline and shoulder rumble strips on rural two-lane roads resulted in a decrease in single vehicle run-off-road, sideswipe-opposite direction, and head-on crashes. The treatment also resulted in a 35-percent reduction (standard error of 10.5 percent) in total target crashes and a nearly 40-percent reduction (standard error of 12.3 percent) in fatal and all injury crashes.
Though these results seem promising, more quantifiable analysis is needed to determine the safety effectiveness of individual treatments installed in combination. Multiplying the crash modification factor (CMF)--a multiplicative factor used to compute the expected number of crashes that might occur after implementing a given countermeasure at a specific site--of individual countermeasures to estimate the combined CMF could overestimate the effectiveness of countermeasure combinations.
Missouri Uses Dynamic Message Signs and Closed-Circuit Video
In 2005, the Missouri Department of Transportation (MoDOT) began its Smooth Roads Initiative, which included improvements to many thousands of miles of the State’s most heavily traveled roadways. To help manage the many construction projects, MoDOT used 40 portable changeable message signs to share information with motorists traveling along three rural highways, including rural interstates.
Recognizing the benefits of the signs, MoDOT decided to seek a more permanent solution for providing realtime information to the traveling public. The agency began a program of installing dynamic message signs and closed-circuit television cameras around the State. In case of an incident, MoDOT can use the cameras to verify the location and severity of the crash and help reduce emergency response times. The agency can employ the signs to warn motorists and direct them to bypass routes when incidents block major roads.
MoDOT received funding from the Rural Safety Innovation Program to install 6 dynamic message signs, upgrade fiber-optic connectivity between the signs, and install 13 closed-circuit TV cameras to relay information to the traffic management center in St. Louis. The agency installed the signs and cameras along I–57, I–55, and U.S. 60. Crews placed the signs upstream from key decision points so that drivers have ample time to change their travel plans based on the information.
The signs display messages 24 hours a day, 7 days a week. Messages may include information about crashes and other traffic-related incidents, work zones, detours, AMBER alerts, weather and pavement conditions, and other emergency information. When no such messages are needed, the signs display public service announcements related to highway safety, such as reminding motorists to buckle up or not to text and drive.
The cameras offer a continuous source of realtime surveillance of the transportation system, enabling MoDOT staff to monitor traffic and weather conditions, assess the impacts of crashes and construction on traffic flow, and manage incidents.
“The installation of closed-circuit TV cameras in rural parts of the State has significantly increased MoDOT’s ability to quickly assess and respond to events as necessary,” says Jon Nelson, a traffic management and operations engineer with MoDOT. “Benefits range from active monitoring of traffic backups to remote assessments of road conditions during inclement weather.”
The rural dynamic message signs have improved the agency’s communications with motorists too. Nelson continues, “The signs allow MoDOT to reach motorists with realtime, relevant traveler information. The signs can improve safety by providing advance warning of slowed or stopped traffic resulting from an incident or roadwork. They can also provide information that motorists may find helpful, such as detour routes or expected adverse weather conditions.”
Results. MoDOT hired researchers at the University of Missouri in Columbia, MO, to conduct a formal evaluation of some of the signs deployed along the target roadways. Their evaluation drew from the results of three studies. The first surveyed motorists in person at two truck stops in the study region. Motorists were asked about sign visibility, message clarity and accuracy, the perceived effect of the signs on safety, and whether the driver took action (such as slowing down or changing his or her route) based on the sign’s message. Overall, the surveyed motorists seemed to be very satisfied with MoDOT’s use of dynamic message signs in rural areas, and 94 percent said they took the action suggested by the signs.
In the second study, MoDOT conducted field observations to assess the effectiveness of the dynamic message signs in alerting drivers of an upcoming work zone. MoDOT observed speed changes at two construction work zones on I–55. One site consisted of a permanent sign upstream of the work zone, and the other site consisted of a portable sign upstream of the work zone. The researchers observed average speed decreases of 3.64 miles per hour, mi/h (5.86 kilometers per hour, km/h) and 1.25 mi/h (2.01 km/h) at the first and second sites. The research team found the speed reductions to be statistically significant, indicating that the dynamic message signs had positive effects on safety.
The third study evaluated the effectiveness of the signs in detouring traffic around a full freeway closure. MoDOT surveyed motorists in the affected area to determine if they were aware of the closure and detour, and to what extent they relied on the dynamic message signs to obtain traveler information. Overall, motorists said they were satisfied with the information provided through the signs, trusted the accuracy and sufficiency of the detour information, and followed the recommendations the signs provided. About 41 percent (45 out of 109) of the respondents were aware of the bridge closure solely because they saw a dynamic message sign and not through other means such as a radio or newspaper announcement. In addition, the researchers noted a significant increase in traffic flow on the detour route during closure days, along with a corresponding decrease in traffic on the normal route.
Conclusions. MoDOT generally found motorists to be very appreciative of information the agency is able to provide thanks to the dynamic message signs and closed-circuit TV cameras. Further, agency officials believe these safety measures are cost effective. To date, the maintenance costs have been minimal, while the range of benefits is substantial, including continued system surveillance, provision of valuable information to travelers, monitoring of traffic incidents and work zones in real time, and verifying weather and pavement conditions.
“The rural dynamic message signs allow us to communicate directly with motorists in the immediate vicinity of a work zone, incident, or other traffic condition,” says Nelson. “Often . . . it is the most efficient and effective way for us to get critical traveler information to our customers so they can respond accordingly. If we’re unable to provide customers with critical information about an event through traditional communication means, there’s always that last opportunity to reach them via a dynamic message sign.”
MoDOT also discovered that coordinating with the six electric cooperatives operating in the study region was crucial to the success of the project. Each had its own policies and procedures for providing power to the signs and cameras, and response times varied from one electric company to the next. Without the cooperation of these electric companies, project work was subject to snags.
MoDOT officials also reported that the agency has installed additional dynamic message signs and closed-circuit TV cameras since the completion of the project in order to fill gaps in its existing traffic monitoring system. Although these deployments were not a direct result of the Rural Safety Innovation Program, its success created additional support and justification for the subsequent installations.
Future Considerations In Evaluating Safety Effectiveness
Quantifying the safety effectiveness of specific countermeasures and presenting lessons learned offers benefits to other highway agencies by providing important information to help their States make funding decisions about future safety improvements.
Future research should focus on safety treatments that are not yet in widespread use or for which the information on safety effectiveness is limited. The lack of consistent, accurate data documenting the implementation of safety treatments, when and where they occurred, and before-and-after crash rates at those locations make this type of research challenging.
Highway agencies typically do not keep records identifying the locations of safety improvements and their installation dates. In many cases, maintenance crews install safety improvements without documenting them as such. Crews record the improvements in maintenance or construction documents without labeling them as safety improvements or formatting the information in a way that is conducive for safety-improvement evaluations. FHWA is working with States to improve their documentation of safety improvements.
In addition, data on traffic volumes showing exposure levels is critical in performing safety evaluations, along with accurately assigning crash data to specific locations as part of the electronic databases that link to roadway inventories and traffic volume data.
To eliminate many of the challenges in performing evaluations of safety treatments, State and local highway agencies should consider improving the quality of data linking crashes to roadway inventory, traffic volume, and safety treatments. FHWA’s Office of Safety is developing a program to assist State and local agencies in improving and expanding their inventories of roadway data. Known as the Roadway Data Extraction Technical Assistance Program, it will provide the agencies with better data for safety analysis and other purposes.
“The [program] will assist States in identifying, extracting, and recording model inventories of roadway elements from commonly available existing sources of data, such as State roadway photo logs and street view maps from Bing® and Google EarthTM mapping services,” says Robert Pollack, a transportation specialist at FHWA. “A data extraction tool is in pilot testing and is expected to be available by summer 2015.”
Darren Torbic, Ph.D., is a principal traffic engineer for MRIGlobal. He conducts research in highway safety, geometric design, traffic engineering, and bicycle and pedestrian transportation research. Torbic holds three degrees (B.S., M.Eng., and Ph.D.) in civil engineering from the Pennsylvania State University and a B.S. in physics from Westminster College.
John Campbell, Ph.D., is a research leader at Battelle Memorial Institute, where he leads a team that provides a human-centered approach to the development and evaluation of transportation programs, products, and systems. He has a master’s degree in human factors and earned a Ph.D. in cognitive psychology from Claremont Graduate University.
Roya Amjadi is a civil engineer at FHWA’s Turner-Fairbank Highway Research Center in McLean, VA. She manages the Development of Crash Modification Factors program. She has a bachelor’s degree in mechanical engineering and a master’s degree in civil engineering from Cleveland State University.
For more information, contact Roya Amjadi at 202–493–3383 or email@example.com or see the Delta Region Transportation Development Program: Rural Safety Innovation Program Evaluation Final Report (FHWA-SA-14-029) at http://safety.fhwa.dot.gov/local_rural/delta/rsip_finalrpt052114.pdf.