Performance of Longitudinal Barriers on Curves and Super-Elevated Roadway Sections

<p><font size="3">Longitudinal barriers are roadside safety devices commonly used to shield errant vehicles from impacting hazards located alongside the traveled way. These barriers have been successfully designed in many different variations ranging from rigid concrete parapets to semi-rigid beam guardrail to relatively flexible wire rope barriers. Historically, the development and testing of longitudinal barriers has been done under the assumption that the barriers are installed in relatively straight sections parallel to the roadway. While the barriers designed under this assumption have performed well, their behavior when installed on curved roadways is largely unknown. However, despite this lack of understanding of their safety performance on curved roadways, longitudinal barriers are commonly installed on super-elevated curves to protect errant motorists.</font></p> <p><font size="3">Curved, high-speed roadways generally employ super-elevation in order to make the roadway curvature easier for vehicles to navigate. Several potential concerns arise when longitudinal barriers are installed on super-elevated, curved roadway sections. First, barriers on curved roadways effectively increase the angle of the vehicle with respect to the barrier during an impact due to their curvature. This increase in the impact angle can cause an increase in impact loading that may potentially exceed the capacity of barriers designed for impacts parallel to the roadway. Occupant risk measures such as Occupant Ridedown Acceleration (ORA) and Occupant Impact Velocity (OIV) may also increase in magnitude. In addition, the increase in impact angle may raise the potential for vehicle instability due to vehicle snag on posts or other barrier elements and may reduce the barrier's ability to capture and interlock the impacting vehicle, thus resulting in the potential for vehicle underride or override of the barrier. Finally, the super-elevation creates a sloped roadway condition adjacent to the longitudinal barrier that is not considered in standard longitudinal barrier design. This issue is often addressed in bridge rail installations by installing the barrier normal to the super-elevated road surface. However, installation of beam guardrail and wire rope barriers cannot reasonably follow the same recommendation due to the difficultly of driving or embedding the support posts at angles other than vertical. Thus, the orientation of these types of barriers with the road surface is normally significantly different from their design and tested configuration, and there is concern that the change in orientation could lead to vehicle instability. This issue is further complicated when the barrier is installed perpendicular to the road surface on the inside of the curve or lower side of the super elevation. Vehicles approaching from the upper portion of the super elevation may be "ramped" due to barrier orientation perpendicular to the road surface. Barriers may perform better on the lower edge of the super elevation if they are installed vertical.</font></p> <p><font size="3">A need exists to investigate the performance of longitudinal barriers on super-elevated, curved roadways in order to quantify their performance and provide guidelines for their safe application.</font></p> <p><font size="3">The objective of this research effort is to define performance limits for longitudinal barriers when installed on super-elevated, curved highways according to the safety criteria recommended in the Manual for Assessing Safety Hardware (MASH). These performance limits will then be used to generate guidelines for barrier placement on curves.</font></p> <p><font size="3">The first task is a literature search to identify all previous curved guardrail testing and to identify typical curve geometries and super elevations used by the state DOTs. This background material will provide a baseline for the analysis. In the second task, the researchers will simulate previous curved barrier tests using LS-DYNA to validate the performance of the model with respect to impacts with super-elevated curves and longitudinal barriers. Once the previous crash test simulations are validated, LS-DYNA will be used to simulate the performance of the longitudinal barriers on super-elevated curves. Four longitudinal barrier types should be investigated including conventional height and 31-in. high W-beam guardrail and safety shape and vertical-face concrete barriers. Simulation will be used to identify the critical curve radius and super-elevation that results in vehicle instability and poor safety performance for the various barrier types. It will also be used to identify critical vehicle types, 1100C or 2270P, for the barrier and super-elevated curve combinations. </font></p> <p><font size="3">In the third task, full-scale crash testing will be conducted on the barrier types and super-elevated curve combinations identified as critical in the computer simulation effort. The testing will be conducted under the Test Level 3 (TL-3) impact conditions of MASH. The results of the initial crash tests will be used to refine the simulation models and to aid in further refinement of the critical radius and super-elevation for each barrier type. For example, if the initial test of the critical radius and super-elevation fails, then the test data will be used to revise the model, and further simulation will determine a new, less severe combination of the critical radius and super-elevation. If the test passes, then the simulation will be used to determine a new, more severe combination of the critical radius and super-elevation. A second round of full-scale crash tests may then be conducted on longitudinal barriers installed at the refined super-elevated curve geometry. In the fourth task, the results of the testing and simulation will be used to develop performance limits for the longitudinal barriers installed on super-elevated curves. In addition, the knowledge gained from the evaluation and testing of longitudinal barriers on curved roadways will be used to make recommendations with regard to the end terminals and transitions on curves. Recommendations will also be made with regard to future research on longitudinal barriers on super-elevated, curved roadways in areas that were outside the scope of this problem statement, including TL-4 barriers and wire rope barriers. In the last task, a final report will be prepared: a summary report to document the analysis, testing, and performance limits generated during the research project.</font></p>


  • English


  • Status: Proposed
  • Contract Numbers:


  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  USA  20001
  • Project Managers:

    Harrigan, Edward

  • Start Date: 20100618
  • Source Data: RiP Project 26559

Subject/Index Terms

Filing Info

  • Accession Number: 01463899
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: 22-29
  • Files: TRB, RiP
  • Created Date: Jan 3 2013 2:32PM