RADIOLUMINESCENT LANE DELINEATORS FOR WET-NIGHT VISIBILITY

A theoretical and experimental program was undertaken to evaluate the feasibility of using radioluminescent light sources (with hydrogen-3 or krypton-85) as roadway lane markers. Simulated markers using ultraviolet light stimulation and a ribbed coverplate to counteract Fresnel losses were built and matched to the luminance of actual radioluminescent materials. The radioactivity required to fabricate a comparable single marker is estimated to be 240 curies of hydrogen-3. The luminance when viewed at 1.5 deg, is approximately 1.2 scotopic footlambert (4.1 scotopic cd/sq m). Subjective visibility tests of simulated radioluminescent markers using observers in an instrument test vehicle established the visibility of a dry marker as 350 ft (107 m) and of a wet marker as 275 ft (84 m). These values are greater than the visibility distance for a paint stripe or used retroreflector but are less than the values for a new retroreflector. Radioluminescent markers using hydrogen-3 are therefore sufficiently bright but costs ($1.00 per curie) are high and there is a potential for radiation overexposure in an accident situation at a stockpile or storage facility. /FHWA/