As part of making our transportation system more multimodal, state departments of transportation (DOTs) and other transportation agencies are seeking new design solutions to address mobility and safety for all users in low-speed urban and suburban environments. These environments often feature trees, poles, landscaping, medians, shared paths, and other design elements to improve livability and support increased walking and cycling. 

Where roadside safety barriers are desired in low-speed environments, low-profile barriers designed to address crash risks at lower speed conditions (MASH TL-2) are often favored because they are more compatible with the community context. Yet the space available for crashworthy end treatments for these barriers can be highly constrained in many urban and suburban locations because of closely spaced intersections and driveways, limited right-of-way, and the presence of street trees and other features. In addition, the presence of vertical curbs and adjacent sidewalks or multiuse paths restrict the use of a flared end treatment. Rural locations can have similar constraints and conditions, even without the presence of a curb. 

To balance the needs of all users, community priorities, and location constraints, a viable crashworthy end treatment for barriers in urban and suburban roadside environments needs to minimize:

• Length: short end treatments can be installed along roadways with longitudinal constraints including discontinuities for intersections, driveways, and crossings;
• Width: a narrow cross-section can reduce encroachment into vehicle travel lanes and adjacent pedestrian and multiuse paths; and
• Height: a shorter profile reduces impacts on sight distance and allows the end treatment to be used with low-profile barriers, guardrails, and typical concrete barriers/bridge traffic railings shapes.

To be feasible for implementation, an end treatment must also be cost effective to install and maintain, for new installations and retrofitting existing barriers. 

Research is needed to provide roadside safety design practitioners with a nonproprietary, crashworthy tangent end treatment for rigid barrier systems on low-speed roadways. 

OBJECTIVE

The objective of the research is to develop a nonproprietary, crashworthy tangent end treatment with the following characteristics:  

• Appropriate for urban and suburban environments;
• Of minimal required length, width, and height; 
• Can be transitioned to commonly used rigid barriers  (e.g., TL-2 low profile or TL-3 concrete barriers); and
• Can be placed on top of a 6” curb or placed where there is no curb in advance of the barrier.

RESEARCH PLAN

Anticipated tasks include: 

• Literature review to identify critical design elements, potential components, and to establish baseline for system;
• Review related current and expired patents to ensure a nonproprietary system is developed;
• Develop design concepts; 
• Perform computer simulations to develop and refine design concepts and prioritize which crash tests represent the most critical conditions;
• Present design concepts and prioritized crash tests for NCHRP approval during the interim deliverable review meeting;
• Refine the design; prepare and execute a full-scale crash testing plan to validate the proposed device to MASH TL-2 conditions, optimized to budget constraints; and 
• Provide computer simulation results as part of the engineering justification of crash worthiness for full-scale crash tests in the MASH TL-2 Terminal/Crash Cushion testing matrix that were not conducted as full-scale crash tests.

The final deliverables will include:  

• A report with the following:
  • Documentation of the research activities;
  • Key findings;
  • Design concepts developed;
  • Results of the computer simulations including interpretations with respect to crashworthiness;
  • Results of the crash tests including conclusions with respect to crashworthiness;
  • Design details for the crashworthy tangent end treatment;
  • Potential for uncurbed applications;
  • Guidelines on installation, maintenance, and repair of the end treatment;
  • Estimated installation and maintenance costs;
  • Design drawings of concepts for commonly needed transitions; and
  • Other topics identified during project.
• Downloadable detailed design drawings (.pdf, .dgn, and .dwg formats). 
• Downloadable crash test videos (.wmv or .mp4 format).
• Detailed drawings in the Task Force 13 Hardware Guide format.
• Presentation of the final design to a relevant audience (e.g., the AASHTO Technical Committee on Roadside Safety or the TRB Roadside Design Committee (AKD20)). 
• A stand-alone technical memorandum that identifies implementation pathways, key implementers of the results, and well-defined scopes of work for further dissemination and pilot implementation of the methods. The technical memorandum should provide adequate detail about how state DOTs and other transportation agencies can implement the results of NCHRP Project 22-52.  

STATUS: Research in progress