Traffic sign visibility at night is largely determined by sign luminance. Sign luminance, in turn, is determined by viewing geometry, retroreflective characteristics of the sign material, and headlamp illumination. Computer modeling of sign luminance has advanced to allow sign luminance to be predicted based on data sets of retroreflective material performance and headlamp luminous intensity matrices. This research project sought to assess the amount and variability of illumination provided to sign positions by a sample of Texas vehicles. The Texas Transportation Institute measured vehicle dimensions and headlamp illuminance at prespecified points representing typical sign locations. Data collection included 25 passenger cars and 21 light trucks and vans. Vehicles were measured without aiming, but after cleaning the headlamps. Each lamp was measured independently and total illuminance at sign locations was calculated. The project found that the vehicle dimensions specified in computer models encompassed the vehicles measured. The illumination values obtained were also in the range of those provided by the composite lamps in the existing computer models. Theoretical sign luminance values for different types of retroreflective sheeting were calculated using the median illumination values from the vehicles measured. The project confirms the validity of using computer models to predict sign luminance. It also confirmed current TxDOT retroreflective sheeting policy. It is recommended that TxDOT consistently aim the headlamps of vehicles used to perform nighttime sign inspections to assure consistency of sign appearance.Year Make Model Class 1 1988 Chevrolet 1500 LTV 2 1989 Nissan Pathfinder LTV 3 1990 Ford F-150 XFT LTV 4 1995 Chevrolet 3 ... LTV 9 1998 Dodge Durango LTV 10 1998 Toyota RAV 4 LTV ll 1999 Ford F-150 LTV 12 2000 Ford F -150 LTV 13 2000 Ford F-250 LTV ... LTV 21 2003 Kia Sedona LTV 22 1990 Pontiac Grand AM Sedan 23 1992 GM Satum Sedan 24 1995 Ford Mustang Sedan 25 1995anbsp;...
|Title||:||Headlamp illumination provided to sign positions by passenger vehicles|
|Author||:||Susan T. Chrysler, H. Gene Hawkins, Paul John Carlson, Texas. Dept. of Transportation, United States. Federal Highway Administration, Texas Transportation Institute|