The options available to designers for traffic barriers include deciding whether or not to include them in the design and, if they are included, deciding which type to choose. The purpose of the barrier, as stated in the AASHTO Green Book, is to “minimize the severity of potential accidents involving vehicles leaving the traveled way where the consequences of errant vehicles striking a barrier are less than leaving the roadway.” In addition to preventing collisions with fixed objects along the roadside, traffic barriers are themselves obstacles and have some degree of accident potential. The use of traffic barriers should consider these tradeoffs.
A wide variety of traffic barriers is available for installation along highways and streets, including both longitudinal barriers and crash cushions. Longitudinal barriers (such as guardrails and median barriers) are designed primarily to redirect errant vehicles and keep them from going beyond the edge of the roadway. Crash cushions primarily serve to decelerate errant vehicles to a complete stop (such as impact attenuators at freeway exit gore areas).
The design of the traffic barrier is an important detail that contributes to the overall look or theme of roadway design; therefore, in addition to safety, the selection of an appropriate barrier design should include aesthetic considerations. In addition, all traffic barriers should meet crash-testing guidelines for the type of roadway being designed. Crash-testing guidelines have different levels, depending on the facility and the type of vehicles that will use the facility. For example, on parkways with restricted truck traffic, many aesthetic barriers have been designed and crash tested. The criteria used for these types of barriers are less stringent than the criteria for facilities with truck traffic. Because aesthetic considerations are usually a factor on parkways, many of these barriers are designed to add to the visual quality of the road. Even for roads that are not parkways, however, there are still many barrier designs that meet the criteria for facilities with truck traffic. Given these options, designers must balance their decisions based on safety, cost, and aesthetics.
An in-depth discussion of the factors associated with the decision to install traffic barriers and guidance on the selection of a particular barrier design is presented in the AASHTO Roadside Design Guide. A concern among some States when selecting a barrier design is cost. Aesthetic barriers might have a higher upfront cost than standard steel barriers and may be more expensive to maintain. One solution to this concern is to be consistent in the type of aesthetic barrier used throughout a State. For instance, a State might want to limit the type of barriers used to only two, an inexpensive barrier for highways where aesthetics is not a major concern and an aesthetic type for highways where visual quality is important. In this way, States can cut back on the cost to maintain multiple barrier designs.
Weathering steel guardrails are an example of an inexpensive barrier that may be considered acceptable in certain surroundings. For many States, weathering steel has been a good solution, because its rustic color helps the guardrail blend into the environment. Weathering steel has, however, had durability problems in a few areas.
Source: Flexibility in Highway Design pp. 94-96
Published: 1997
