Semisequicentennial Transportation Conference Proceedings
May 1996, Iowa State University, Ames, Iowa
Roadside Safety Milestones
Wm. H. Wendling
P.O. Box 119,
Camdenton, Missouri 65020.
Motor vehicle fatality rates have been on a general decline over the past 25 years. In 1965 rates of 25 deaths per 100,000 population, and five per 100 million vehicle miles traveled, were occurring; 1992 rates were 15.4 deaths per 100,000 population and 1.8 per 100 million vehicle miles traveled. While the trends are noteworthy and encouraging, approximately 40,000 people are still being killed annually in motor vehicle crashes. Of this total approximately 30 percent result from single vehicle, run-off-the-road crashes.The vast majority of improvements in roadside safety have occurred since 1960. Prior to that time little attention was given to the roadside; run-off-the-road crashes were attributed to "the nut behind the wheel." This philosophy resulted in untreated guardrail end terminals, unyielding sign and luminaire supports, nontraversable roadsides and ditches, untreated culvert ends, etc. Unquestionably, improvements in roadside safety design have contributed significantly to the death rate decreases. Safety advancements have been through research and the development of cost effective crashworthy hardware; improved geometric features; roadside recovery areas; improved guidelines for the design, selection, and maintenance of safety features; and general acceptance of the "forgiving roadside" philosophy.This paper is an overview of the research and progress made during the past 35-plus years and identifies key areas that need to be addressed in the near future. Selected research, references, and accomplishments thought to be fundamental to the advancement of roadside safety are identified. The emphasis is on research that has been associated with improvements in the safety of the roadside. Key words: roadside, research, safety, design, hardware.
The vast majority of improvements in roadside safety have occurred since 1960. Prior thereto little attention was given to safety of the roadside; run-off-the-road crashes were attributed to the "nut behind the wheel." This philosophy resulted in unyielding sign and luminaire supports, untreated guardrail ends (blunt ends), nontraversable ditches, untreated culvert ends, etc. This paper presents an overview of progress made during the past 35-plus years and identifies problems and key areas that need to be addressed in the near future. This paper is intended to include the formal transportation research oriented efforts that have impacted roadside safety. Some research efforts may not be documented in formal research papers. Some of these efforts are described in brief. An attempt is made in the first section to briefly describe selected publications, activities, events, etc., that have contributed to roadside safety since 1960. The master reference for the majority of this report is a 1994 paper by Dr. Hayes E. Ross, Jr. (1).
Kenneth A. Stonex, Roadside Design for Safety Highway Research Proceedings, Vol. 33, 1960. This paper identified common roadside hazards such as blunt guardrail ends, rigid supports for light poles and sign supports, trees, utility poles, steep side slopes, and unsafe ditch sections. Potential solutions to these problems were presented which were implemented. These were use of breakaway supports, burying the end of guardrail, clearing the roadside of unneeded obstacles, and flattening and rounding slopes and ditch sections.
Proposed Full Scale-Testing Procedures for Guardrails, Highway Research Board Circular 482, September 1962. This one-page circular included the first formalized set of guidelines for testing guardrails.
Highway Safety Act of 1966. This act strengthened state and local safety programs and for the first time placed the federal government in a leadership role to help guide and finance state safety activities.
Highway Design and Operational Practices Related to Highway Safety, 1967 (a report of the Special AASHO Traffic Safety Committee). The first of two "Yellow Books" addressing highway safety issues, this publication identified methods to mitigate roadside hazards. It was in this publication the 30-foot clear recovery area was identified.
Guardrail, Barriers, and Sign Supports, Highway Research Board 174, 1967. Included in this record were several papers dealing with testing and development of the W-beam barrier, development of new highway barriers, and development of guardrail warrants. The record reports established basic height and post spacing for W-beam guardrail still in use today. A paper by J.C. Glennon developed warrants for guardrails to shield embankments. These warrants are still in use today. A paper by M.D. Graham presented results of an extensive theoretical and experimental study through which new barrier designs were developed: strong beam/weak post guardrail, median barrier, bridge rail systems, and improvements in cable rail systems.
J.D. Michie and L.R. Calcote, Location, Selection, and Maintenance of Highway Guardrails and Median Barriers, NCHRP 54, 1969. This report provided recommended standards for consistency of practice related to warrants, design, and maintenance.
Highway Safety Act of 1970. This act established the National Highway Traffic Safety Administration (NHTSA).
U.S. Congressional hearings. Comprehensive hearings were held early in the 1970s on highway safety issues. These hearings concluded that substantial improvements could be made if the Federal Highway Administration took a more active role in highway safety. These hearings led to the safety advancements made with the Highway Safety Act of 1973.
Location, Selection, and Maintenance of Highway Traffic Barriers, NCHRP Report 118, 1971. This report updated and superseded NCHRP Report 54. It presented a synthesis of existing information on warrants, service requirements, and performance criteria for all traffic barrier systems, including longitudinal barriers and crash cushions.
Evaluation of New Guardrail Terminal, Highway Research Board Record 386, 1972. This paper provided information on the development of the Breakaway Cable Terminal (BCT) for W-beam guardrail. The BCT design with subsequent modifications became the most widely used end treatment for W-beam guardrail in the U.S. Other end treatments developed since have utilized the breakaway cable feature of the BCT.
Highway Design and Operational Practices Related to Highway Safety, 1974 (second edition of the report to the AASHTO Select Committee on Highway Safety). This new edition presented both new knowledge and new priorities for highway safety efforts. It incorporated results of research and field experience in the areas of design and operations.
Recommended Procedures for Vehicle Crash Testing of Highway Appurtenances, NCHRP 153, 1974. Report updated the one-page guidelines of the HRB Circular 482 and provided recommendations relative to the testing and evaluation of longitudinal barriers, crash cushions, and breakaway features.
Guide for Selecting, Locating, and Designing Traffic Barriers, AASHTO, 1977. This publication by AASHTO comprehensively addressed the subject of traffic barriers. Its purpose was to summarize the current state of the knowledge and to present specific guidelines that established conditions that warrant barriers; the type of barriers available; their strength, safety and maintenance characteristics; selection procedures; and how the barrier should be installed, dimensionally or geometrically. Also presented were cost effectiveness analysis procedures and barrier design methodologies.
General Computer Program for Analysis of Automobile Barriers, Highway Research Board Record 343, 1971. A paper in this record by G.H. Powell describes the Barrier VII program. Wide use of this program has been made, and continues to be made, in analysis of numerous longitudinal barrier systems. It has proved to be a valuable tool when used properly and within its limits.
Examples of other efforts in 1970 to improve the safety of our roadsides include the development of new crash cushion designs, truck mounted attenuators, and bridge rails for heavy vehicles.
The Rural Mailbox: A Little Known Hazard, Transportation Research Record 769, 1980. This paper focused national attention on the problem of hazardous mailbox installations and presented safe designs. Subsequent research has resulted in vastly improved rural mailbox design.
Recommended Procedures for the Safety Performance Evaluation of Highway Appurtenances, NCHRP 230, 1981. This report updated and superseded NCHRP Report 153 and TRB Circular 191. It incorporated new procedures, updated the evaluation criteria (introduced the flail space model), and updated procedures with available technology and practices.
Safety Treatment of Drainage Structures, Transportation Research Record 868, 1982. This report includes results of a study in which safety treatments to transverse and parallel drainage structures were developed. Results have been used throughout the United States.
Roadside Design Guide, AASHTO Task Force for Roadside Safety, 1988. This guide updated and superseded the 1977 AASHTO Guide for Selecting, Locating and Designing Traffic Barriers. The updated version addressed roadside safety and economics, roadside topography and drainage structures, sign and luminaire supports, and safety appurtenances for work zones.
Development of new end treatments occurred in the 1980's. These included the Safety End Treatment (SENTRE), the Transition End Treatment (TREND), the Vehicle Attenuating Terminal (VAT) and its second generation (CAT), and the ET-2000, as well as modifications to the turned down and Breakaway Cable Terminal (BCT).
Recommended Procedures for the Safety Performance Evaluation of Highway Features, NCHRP 350, 1993. This report updated and superseded NCHRP 230. Key changes included guidelines for evaluating a wider range of features, adoption of the 2000K (I-ton) pickup truck to represent the upper end of the passenger vehicle spectrum, provisions for testing to a wider range of levels from which different service levels system may be developed, provisions for optional test methods for side impact testing, and adoption of the SI units of measure. In response to Section 1073 of the 1991 Intermodal Surface Transportation Efficiency Act (ISTEA) that required the Secretary of Transportation to issue a final rule implementing revised guidelines and standards for acceptable roadside barriers and other appurtenances, for the first time FHWA has officially adopted a crash performance standard, NCHRP 350.
Single Slope Concrete Median Barrier, Transportation Research Record 1302, 1991. The record describes development of a new type of concrete median barrier incorporating a single slope configuration. The barrier shape improved impact performance, especially for the small vehicle, in comparison to the New Jersey configuration. A second advantage of this barrier is that if designed correctly it would not require resetting each time the adjoining surface is overlaid.
Geometric Design, Roadside Safety Features, Roadside Hardware Monitoring, and Scenic Tours, Transportation Research Record 1500, 1995. This publication contains 10 reports related to roadside hardware and roadside safety and 13 other reports pertaining to safety design of roadways.
Major accomplishments have been made over the past 35-plus years in roadside safety design. The majority of the improvements are attributed to improvements in "roadside hardware." Following is a summary of the principle improvements.
Roadside and Median Barriers and Bridge Railings
Strong post (wood or steel) W-beam 6-foot-3-inch post spacing, 27-inch rail height for roadside applications. This is the most widely used roadside barrier. It replaced a similar system with 12-foot-6-inch post spacing with a rail height of 24 inches. A 30-inch height version is used with back-to-back W-beams for median barriers.
Concrete safety shaped barrier (commonly called the New Jersey barrier). The most widely used median and bridge rail barrier in the U.S. Precast barriers of its type are widely used in work zones.
Single slope concrete barrier. This recently developed system is gaining popularity.
Thrie beam roadside and median barriers. This system is widely used by some states for roadside and median barriers.
Bridge railings. Since adoption of performance criteria for bridge railings by AASHTO, considerable research has been done to ascertain the adequacy of existing railings and develop new rail systems to meet the criteria.
Turned down W-beam. Based on recommendations of engineers at the General Motors Proving Grounds, the turned down W-Beam was developed to reduce the severe hazard of the blunt end guardrail.
Breakaway cable terminal (BCT). This system was developed as an alternative to the turned down treatment. Its use grew during the 1970s and 1980s. Its performance was good when installed and maintained properly. Performance with small cars has been a problem.
Proprietary systems. Several new and innovative proprietary end treatments have been developed and are becoming widely used.
Steel drum crash cushions. This system is believed to be the first operational crash cushion.
Proprietary systems. Innovative proprietary crash cushions have been developed: sand filled barrels, water filled tubes, hex foam cartridges, steel and plastic tubes.
Embankments, ditches, driveways, and crossovers. These features have been improved through limited crash testing and computer simulation models.
Curbs. The use of curbs along high-speed roadways has been in disfavor for many years.
Breakaway supports. The breakaway feature was a key factor in making the "forgiving roadside" a reality.
Drainage structures. Safety treatment of transverse and parallel drainage structures, sloped ends, and grates are widely used.
Traffic devices. Safer traffic control devices have evolved over the past 20 years and include safe sign supports, channelizing devices, barricades, cones, drums, and vertical panels.
Truck-mounted attenuators. The expansion of maintenance and work zone activities prompted the development and use of TMAs.
Mailbox supports. Advancements in the safety of mailbox supports have been made over the past 20 years.
Emergency call box supports. Safe supports for traffic call boxes are now widely used.
Installation and Maintenance Procedures
The proper installation and maintenance of safety features remains a first-level concern. Installation and maintenance problems are in general proportional to the degree of design complexity. The highly desirable maintenance features in all highway hardware are those of simple design of readily available, standard parts. What can and will be done to improve the quality of installation and maintenance of safety features?
Many new and advanced materials are being introduced into the transportation industry: composites, high strength concrete, recycled rubber and plastics, etc. Which materials are suitable for use in roadside safety features? Can these materials be cost effective in roadside safety design? What studies are needed to define the necessary properties and characteristics of these materials?
The W-beam rail developed in the mid 1930s is widely used for rail elements in barrier systems. Will these elements satisfactorily meet NCHRP 350 performance requirements? Is there a cost effective rail shape that will provide improved field performance? Is it possible to improve our selection of barrier systems, considering performance, cost effectiveness, and design flexibility?
The ISTEA of 1991 recognized the trend toward increased vehicle fleet of sport and utility vehicles, vans, and pickups. In adopting NCHRP 350, the FHWA verified and accepted and mandated through the ISTEA highway safety features designed to accommodate these vehicles. Is the light truck the proper test vehicle? Does this vehicle address the future needs of roadside safety features? The crash performance standards have been evolving since the 1960s. What should be the future of NCHRP 350? Are the specified impact conditions correct for field performance for the vehicle mix?
Slopes and Ditches
Only limited research has been performed on the effects of slopes and ditch configuration as related to the severity of run-off-the-road crashes. What are the critical slopes as related to speed and crash severity? What are the critical effects of ditch configurations as related to critical slopes and crash severity?
Field Performance Evaluation Procedures
Field performance evaluation of roadside safety features have been encouraged over the past 35 years. During the 1970s when new roadside safety features were being implemented, formal evaluations were performed and documented. Little effort is being given today to evaluate the field performance of safety features. NCHRP 230 first presented guidelines for in-service performance evaluations. Chapter 7 of NCHRP 350 revisits the area. This document states, "The in service evaluation step is necessary as analytical and crash test experiments described in previous chapters only partially assess the efficacy of feature and more thorough and in-depth knowledge of the feature is needed." This statement is especially true as our vehicle fleet continues to change. Is it possible to include sufficient field performance evaluations of roadside safety features to recognize changes in performance and maintenance needs?
- H.E. Ross, Jr. Evolution of Approaches to Address the Roadside Safety Problems. Paper presented at Roadside Safety Workshop TRB A2A-04 Committee Meeting, Woods Hole, Massachusetts, August 1994.