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Locations which would benefit from the installation of supplemental advance warning devices typically exhibit safety and/or operational problems. Establishing the need for supplemental devices, therefore, requires identifying the problem locations and performing a safety and/or operational analysis. Deficient locations can be identified by a traffic safety management system, citizen complaints, employee observations, and by safety […]

Designing a warning device that provides a clear, unambiguous message to the motorist can be a difficult task. The difficulty is due in part to the concern of the engineer to act in a “reasonable and prudent” manner. Increasing motorist safety and minimizing lia­bility require that the device provide a readily understood and unambiguous message. […]

Estimates by the FHWA indicate that there are an average of 15 signs per mile on the nation’s 3.8 million miles of streets and roadways [6]. The resultant 57 million traffic signs represent a huge investment in materials, labor, equipment, and maintenance costs. While this is a significant investment, improvements using standard traffic control signing […]

While the advantages of uniformity far outweigh the disadvantages, there are some undesirable effects when complete uniformity is maintained. One of the principal disad­vantages is that strict uniformity may result in the failure to adopt an improved device or procedure simply because it is not in common use. In addition, total uniformity would require the […]

PART 1 SIGNING Brian L. Bowman, Ph. D., PE. Professor of Civil Engineering Auburn University Auburn, Alabama Part 1 of this chapter presents a comprehensive review of the design, construction, and maintenance of highway signs. Both single — and multiple-mounted sign supports are addressed, with an emphasis on highway safety. Breakaway supports with various types […]

For proper performance, crash cushions should be placed on level terrain with a clear path between the roadway and the attenuator so the vehicle can strike at normal height, with the suspension system in a neutral state. Avoid curbs or slopes in front of the device. Install the attenuator on a smooth surface (usually concrete) […]

Selection of the most appropriate crash cushion depends on site characteristics, perfor­mance of the systems, maintenance characteristics, and life-cycle cost. Both the geometrical conditions encountered and the space requirements for the different systems vary widely. Obstacles greater than 16 ft (5 m) wide can be shielded by systems such as arrays of sand-filled barrels, or […]

Crash cushions are impact attenuators developed to prevent errant vehicles from impacting fixed obstacles. The crash cushion should either decelerate the vehicle to a safe stop, such as in a head-on hit, or redirect it safely away from the obstacle, in the case of a side hit. Crash cushions are typically used where fixed objects […]

Barrier terminals and crash cushions are developed to gradually decelerate an impact­ing vehicle to a stop or to suitably redirect it. Otherwise, untreated ends of barriers and fixed objects can cause severe accidents. A crashworthy end treatment is essential if a barrier terminates within the clear zone or other area where it is likely to […]

Most of the principles previously discussed for median transitions (Art. 6.9.3) apply here as well. Transition designs should gradually stiffen the approach system to avoid vehicle pocketing, snagging, or penetration. Some considerations of importance follow. The concepts are appropriate for both new construction and retrofits. • The splice between the rail of the approach barrier […]