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46 being used at airports in snowplowing operations and its accumulations that can cover up painted markings, the laser potential utility is unclear. lines could convey the location, layout, color, and importance of these markings (76, 77). Enhanced vision systems typically use imaging sensors to penetrate weather phenomena such as darkness, fog, haze, rain, ADDRESSABLE MESSAGE BOARDS or snow; the resulting enhanced scene, a sensor image, is pre- sented on a head-up display (72). The display is normally A 2002 demonstration project installed addressable electronic projected onto the windshield or through a separate display. signs that could display programmed advisory messages on The use of head-up displays in snow removal vehicles may an LED display at taxiway/runway intersections or other areas be an issue, however, as their use demands an undue amount of interest. Its intent is to supplement standard hold position of attention and makes them prone to such adverse effects as signs, address problematic areas on an airport, or convey SA distortion, luminance contrast differences, dark adaptation information to ground operators (76). inhibition, and object misrepresentation (73, 74). IN-GROUND LIGHT EMITTING DIODE MICROWAVE MOTION SENSORS The in-ground LED is a commercial transportation-grade Microwave motion sensors consist of microwave transmit- LED light strip encased in a linear strip of clear plastic and ters located at the hold lines of runways or wherever vehicles placed along hold lines. The intent of the in-ground LED need to be monitored. The transmitters can selectively detect light strips is to accentuate runway and taxiway signage and incoming or outgoing traffic and send a signal to an enunci- markings (i.e., hold-short lines) that may become obscured ator located in the ATCT or elsewhere. A receiver device in during low light and low visibility weather conditions (76). a vehicle could play a prerecorded voice warning, or transmit Although functional in low visibility situations, it is not clear an audio or light warning to the driver in response to each of how they would function in snow removal situations. the signals sent by the microwave transmitters. The microwave transmitters are impervious to weather conditions (75, 76). RUNWAY GUARD LIGHTS GROUND MARKER SYSTEM Runway guard lights (RGL) are currently required by the FAA for airports that have an approved SMGCS plan for conduct- A ground marker system is designed to transmit locally a voice ing operations during low visibility conditions or at airports message to the cockpit of an airplane or the cabin of a vehicle that have an operational need. The RGLs enhance the standard to alert the operator of his or her position on the airport sur- visual cues, signs, and markings used to mark the location of face. The system is activated when an aircraft or vehicle is the holding position. Because RGLs are an international stan- detected by inductive loops in the pavement. An in-cab vehicle dard and are visible in both day and night operations, RGLs warning system using wireless communication supported by provide added surface safety during all weather conditions. dedicated short-range communications is also being investi- gated. Dedicated short-range communications is the technol- ENHANCED RUNWAY LEAD-ON LIGHTS ogy used on toll highways for recognizing vehicles. As applied to airports, dedicated short-range communications data can Effective February 1, 2007, Advisory Circular 150/5340-30C, be transmitted from a runway edge monitor or taxiway sensor Design and Installation Details for Airport Visual Aids, to a vehicle in-cab alerting system (rather than to the marker changed runway lead-on light standards to include a modi- system used for arriving aircraft) to warn the driver that it is not fied color pattern of taxiway centerline lead-on lights (78). safe to enter a runway or other airport surface (76). The modification requires alternating yellow and green lights from the hold-short line to and from the runway to indicate a runway environment. On the taxiway, the centerline lights LASER LIGHT HOLD LINES are green up to the hold-short line. A laser enhancement program functions by projecting a bright light across the first solid line of the hold position markings ENHANCED TAXIWAY SURFACE MARKINGS thereby emphasizing the hold position markings. The laser and optic assembly device straddles the end of a hold line and Advisory Circular 150/5340-1, Standards for Airport Mark- projects a line or shaped beam of laser light along the surface. ings, was issued in April 2005, requiring airfield markings When shown in adverse weather conditions such as rain, snow, standards to change to enhance markings effective June 30, or fog, it creates a low profile three-dimensional line that is 2008, for airports with 1.5 million or more annual passenger far more noticeable than traditional low visibility lighting aids. enplanements (79). In August 2007, FAA initiated an indus- The technology has the capability to project lines in red and trywide call to action that recommended all 14 CFR Part 139 yellow laser illuminations. In areas that are subject to snow airports install enhanced taxiway and hold-short markings,