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Roadways 45 Chapter 2C contains provisions for warning signs which are typically diamond shaped. Warn- ing signs, as defined by the MUTCD, give notice to road users of a situation that might not be readily apparent. Section 2A.16 provides guidance for sign location in terms of distance from the edge of the road and sign height. 3.5 Sign Structures and Illumination 3.5.1 Sign Structures Road signs can be ground mounted on the roadside or mounted overhead on sign structures. In general, signs should be located on the right side of the roadway (MUTCD Section 2A.16) so that they do the following: Are outside the clear zone unless placed on a breakaway support (see Section 3.5.2), Optimize nighttime visibility, Minimize the effects of mud splatter and debris, Do not obscure each other, Do not obscure the sight distance to approaching vehicles on the major street for drivers who are stopped on minor-street approaches, and Are not hidden from view. For added emphasis, supplemental signs may be added to the left side of the roadway. The MUTCD offers guidance on when overhead sign mounting may be justified (Section 2A.17). The following conditions (not in priority order) may be considered in an engineering study to determine if overhead signs would be beneficial: Traffic volume at or near capacity; Complex interchange design; Three or more lanes in each direction; Restricted sight distance; Closely spaced interchanges; Multi-lane exits; Large percentage of trucks; Street lighting background; High-speed traffic; Consistency of sign message location through a series of interchanges; Insufficient space for ground-mounted signs; Junction of two freeways; and Left exit ramps. For airport applications, it is recommended that overhead signs be used for lane assignment on approach to terminal buildings, particularly for multi-lane facilities, and at any other loca- tions where lane assignment is considered critical for safe and efficient roadway operations. AASHTO offers guidance on sign support materials, types, design, and wind load ratings for large and small signs14,15. These supports should be designed and located in a manner that main- tains a safe roadside environment for all roadway users, and does not distract from the primary purpose of the signs which is to guide, warn and regulate traffic. For these reasons, architectural features and graphic treatments on sign structures (such as banners or other messaging) should be limited and carefully placed if used.

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46 Wayfinding and Signing Guidelines for Airport Terminals and Landside 3.5.2 Safety Considerations Sign structures should be mounted on breakaway supports or be shielded by guard rail. Road- way lighting luminaires should also be breakaway. The FHWA offers an informational guide to the various types of sign and lighting structures and supports16. Signs should be placed off the roadway to allow a roadside clear zone to prevent errant vehi- cles from striking sign structures. If such a clear zone can't be provided because of limited right of way, large sign structures, including static and CMS signs, may need to be protected with crash cushions or guardrails. Additional information can be found in the AASHTO Roadside Design Guide17. Any roadway work zone device, such as temporary signs, barricades, and barrels, must meet crash worthiness standards as well18,19. 3.5.3 Illumination The MUTCD requires roadway signs to be illuminated or to use retroreflective materials in order to provide proper nighttime visibility. Because of the high ambient light levels along road- ways in most major airports (from terminal buildings, parking garages, and landscaping) it may be necessary to use external or internal illumination to provide adequate nighttime visibility for roadway signs. At smaller airports or on the outlying areas of larger airports, with lower ambient light levels, high quality retroreflective materials may provide adequate visibility, particularly for ground-mounted signs. Nighttime testing on-site will be required to make these determinations. The Illuminating Engineering Society provides guidance on roadway sign lighting20. Other factors to consider when deciding between retroreflective materials and external or internal illu- mination are the following: Traffic volumes; Complexity of road geometries (i.e., retroreflective material typically works when used head-on, and is not ideal for curving roads); Obstructions of vehicle headlamps from one sign to the next due to closely spaced signs or landscape elements; and Need to emphasize decision points or critical information including terminal/airline listings. 3.5.3.1 Retroreflective Sign Sheeting Retroreflective sign sheeting materials return light from vehicle headlamps to the driver's eyes. Retroreflection is achieved either through microscopic glass beads with a thin metallic backing or through microprisms in a thin polycarbonate film. These materials vary in the daytime color appearance and in their nighttime brightness and efficiency with which they reflect the vehicle headlamps. The FHWA and most states require a minimum level of retroreflectivity for all road- way signs and provide a toolkit to ensure these values are met21. In some airports, the roadway horizontal and vertical geometry is such that considerable care must be taken by the designer in sign location and orientation to ensure that vehicle headlamps will adequately illuminate the sign along the necessary roadway sections. The use of high quality retroreflective sheeting in place of external illumination may also help airports reduce electricity and maintenance costs and reach sustainability goals. Elimination of external illumination also reduces light pollution. 3.5.3.2 External Sign Illumination Roadway lighting is addressed in a guide produced by AASHTO. This guide addresses sign lighting in different ambient lighting conditions. The guide recommends retaining external sign illumination in high ambient conditions. Most major airports would meet this condition22. Sign