Guide for Selecting, Location, and Designing Traffic Barriers
|Publication Date:||1 January 1977|
Purpose of Guide
Since the publication of NCHRP Report 11 8 (1) , additional research has been done in the traffic barrier area and additional inservice experience has been gained on existing traffic barrier systems. The purpose of this document is to summarize the current state of knowledge and to present specific design guidelines for highway traffic barriers. The guidelines establish the conditions which warrant barrier protection. 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 in the guide is a cost-effective selection procedure. This procedure is presented as an alternate to the more conventional selection procedures. In the conventional procedures. barrier need is usually based on an evaluation of the relative hazard of the barrier versus the hazard of the unprotected obstacle. The barrier is warranted if the obstacle is more hazardous to the motorist than the barrier itself. In the cost-effective procedure, need is based on an evaluation of the costs associated with the barrier versus the costs associated with the unprotected obstacle. Initial costs. maintenance costs, and accident costs are included in the evaluation. In addition to establishing need, the procedure can also be used to compare the cost-effectiveness of various barrier systems.
For the purpose of this guide all traffic barriers are classified as one of two basic types. namely, longitudinal barriers and crash cushions. Longitudinal barriers function primarily by redirecting errant vehicles. Crash cushions function primarily by decelerating errant vehicles to a stop. Roadside barriers (called guardrails, guiderails, guidefences, etc.), median barriers, and bridge rails are the three types of longitudinal barriers. Each of these types performs a particular function as does the crash cushion and these functions are delineated in this guide.
It has been said that a traffic barrier is like life insurance-it is good to have as long as it is not needed. Although this is an overstatement, it cannot be overemphasized that a traffic barrier is itself a hazard. Every effort should be made in the design stage to eliminate the need for traffic barriers. Existing highways should be upgraded when feasible to eliminate hazardous conditions that require barrier protection. A traffic barrier should be installed discriminately and only when it is unfeasible to remove the hazardous condition.