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.