King K Mak

Crashworthiness of roadside features across vehicle platforms

Each year more than 14,000 persons are killed and 1 million persons are injured as a result of roadside crashes. Recent estimates of the annual societal costs associated with these roadside crashes amounted to

Roadside Safety Analysis Program: A Cost-Effectiveness Analysis Procedure

80 billion. Clearly, there is a need for further understanding of the roadside safety problem. The impact performances of roadside safety features are typically evaluated through full-scale crash testing with two vehicles selected from the extremes of the passenger vehicle fleet in terms of weight and size. The implicit assumption is that if a roadside safety feature successfully passes the test requirements for vehicles at the extremes for the fleet, the feature will perform satisfactorily for all other vehicles in between. Many vehicle parameters could influence performance during impacts, and this assumption may or may not be valid. The safety performances of roadside features for various passenger car platforms and light-truck subclasses were evaluated. The study approach consists of evaluations of the frequency and severity of roadside crashes for these generic platforms and subclasses by using recent crash data from the Fatal Accident Reporting System, the General Estimates System, and the Highway Safety Information System.

Identification of Vehicular Impact Conditions Associated with Serious Ran-off-Road Crashes

Brief descriptions are provided of a new cost-effectiveness analysis program, known as the Roadside Safety Analysis Program (RSAP), which was developed under NCHRP Project 22-9. RSAP is an improvement over existing cost-effectiveness analysis procedures for evaluation of roadside safety improvements, such as the procedures in the 1977 AASHTO barrier guide and the ROADSIDE program. RSAP improves on many of the algorithms in the procedures and provides a user-friendly interface to facilitate use. The program has undergone extensive testing and validation, including evaluation by an independent reviewer. It is anticipated that RSAP will be available to the public through the McTrans Center at the University of Florida.

CRASH TESTING AND EVALUATION OF WORK ZONE BARRICADES

This report quantifies the characteristics of ran-off-road crashes and identifies appropriate impact conditions for use in full-scale crash testing. Many of the decisions related to design guidelines and policies can benefit from better information on the impact conditions of ran-off-road crashes. The report will be of particular interest to personnel responsible for the design of roadside safety features.

Assessment of NCHRP Report 350 Test conditions

Proper traffic control and delineation are critical to achieving safety in work zones. However, the work zone traffic control devices themselves may pose a safety hazard to vehicle occupants or work crews when impacted by errant vehicles. Thus, there was a need to research the safety performance of work zone traffic control devices to ensure that they perform satisfactorily and meet NCHRP Report 350 guidelines. Several research studies sponsored by the Texas Department of Transportation evaluated the impact performance of various work zone traffic control devices, such as temporary and portable sign supports, plastic drums, sign substrates for use with plastic drums, traffic cones, and vertical panels. Specifically addressed are the studies on barricades. Standard wooden barricade construction was found to be unacceptable due to a demonstrated potential for intrusion of fractured members into the occupant compartment. In response to deficiencies identified in the wooden barricade tests, several alternate barricade designs were developed and successfully tested.

CRITICAL IMPACT POINTS FOR TRANSITIONS AND TERMINALS

The appropriateness of test conditions specified in NCHRP Report 350 was assessed. The assessment focused on the basic Test Level 3 and addressed two areas of interest: the effects of higher speed limit on impact speed and the appropriateness of 25° for the impact angle. The following conclusions and recommendations were drawn on the basis of the results of the analysis: (a) the current test impact speed of 100 km/h (62.2 mph) should be maintained, (b) the current impact angle of 25° for Test 11 of length-of-need sections of permanent longitudinal barriers should be maintained, (c) the test impact angle should be reduced from 25° to 20° for Test 11 of length-of-need sections of temporary longitudinal barriers, and (d) the test impact angle should be reduced from 25° to 20° for Test 21 of barrier transition sections. However, the selection of impact conditions is more a policy decision than a technical issue to be resolved in the update of NCHRP Report 350 guidelines.

NCHRP Report 350 testing of W-beam slotted-rail terminal

Guidelines for evaluating the safety performance of roadside safety features generally recommend that a worst case or critical impact point (CIP) be selected for crash testing. NCHRP Report 350 presents families of curves that can be used to determine the CIP for a transition section. However, these curves have been observed to overestimate the stiffness of a transition system and provide CIP values closer to the more rigid system of the transition (e.g., bridge rail end) than appropriate. New CIP selection curves for transitions are presented. A procedure is provided to aid in determining the CIP for transition sections with multiple rail elements or variations in post strength and post spacing. Various existing and theoretical transitions systems with wide-ranging combinations of beam and post strengths were used to validate the curves. The newly developed CIP relationships for transitions are recommended in lieu of the existing relationships contained in NCHRP Report 350. To facilitate the development of guidelines for the selection of a CIP for terminals, a new definition is proposed. The proposed definition for the CIP is the point along the terminal at which vehicle behavior transitions from gating to redirection. A methodology for determining the CIP using computer simulation techniques is investigated. The data clearly demonstrate that the selection of a single default impact location for all terminal configurations may not provide the CIP for many designs.

ASSESSMENT OF NCHRP REPORT 350 TEST VEHICLES

Two slotted-rail terminal (SRT) designs, one for use on roadways with speed limits of 72.4 km/hr (45 mi/hr) or less and the other for high-speed facilities, were previously developed and successfully crash-tested in accordance with guidelines set forth in NCHRP Report 230. Those SRT designs have been approved by FHWA for use on federal-aid projects. However, FHWA has since adopted NCHRP Report 350 as the official guidelines for safety performance evaluation of roadside features and required that all roadside features to be used on the National Highway System be crash-tested in accordance with the NCHRP Report 350 guidelines by 1998. It is therefore necessary to modify and retest the SRT designs in accordance with NCHRP Report 350 guidelines. The modified SRT design has successfully met the guidelines set forth in NCHRP Report 350 for Test Level 3 conditions, that is, 100-km/hr (62.2 mi/hr) and the results of the crash testing. The modified SRT design has been approved by FHWA for use on the national highway system.

TRANSITIONS FROM GUARDRAIL TO BRIDGE RAIL THAT MEET SAFETY PERFORMANCE REQUIREMENTS

The appropriateness of test vehicles specified in NCHRP Report 350 was assessed, including (a) whether the 2000-kg, three-quarter-ton pickup truck should continue to be used as a test vehicle, and if not, what replacement vehicle would be appropriate; (b) whether the 820-kg passenger car should continue to be used as a test vehicle, and if not, what replacement vehicle would be appropriate; and (c) whether another test vehicle should be added to the matrix—for example, an intermediate-sized passenger car. From the analysis, the following conclusions and recommendations were drawn: (a) The three-quarter-ton pickup truck appears to be a good surrogate for the light truck subclasses. The recommendation is to keep the 2000-kg, three-quarter-ton pickup truck as one of the design test vehicles in the update of the guidelines for NCHRP Report 350. (b) A potential problem is the availability of three-quarter-ton pickup trucks with standard cabs. An alternative design test vehicle may be an intermediate-sized sport utility vehicle, (c) The availability of the 820-kg passenger car design test vehicle will be a problem within the next few years. The recommendation is to keep the current test vehicle as long as it is still readily available, or until the NCHRP Report 350 guidelines are updated, and to increase the curb weight to a level consistent with the curb weights of the two smallest passenger cars with reasonably high sales volume. (d) The addition of a third design vehicle—for example, a 1500-kg intermediate-sized passenger car—to ensure that a roadside feature performs satisfactorily across the entire vehicle spectrum is highly desirable but cost-prohibitive. The addition of an intermediate-sized design test vehicle is therefore not recommended except in situations in which there is a perceived concern that the device may not function properly when impacted by an intermediate-sized vehicle.

Wyoming Road Closure Gate

Three guardrail-to-bridge rail transitions were developed and subjected to full-scale crash tests. The transitions were (a) a nested W-beam with W-beam rub rail that transitioned from a W-beam guardrail to a vertical concrete parapet bridge rail, (b) a nested thrie-beam that transitioned from a W-beam guardrail to a tubular steel bridge rail, and (c) a tubular steel transition that transitioned from a weak-post box-beam guardrail to a tubular steel bridge rail. The nested W-beam and the tubular steel transitions were tested and met NCHRP Report 350 Test Level (TL)-3 requirements. The nested thrie-beam transition was tested and met TL-4 requirements.