Abstract
The effects of weather and illumination on a freeway ramp driver's decision to accept or reject a mainstream gap has been studied by a photogrammetric technique. The photo coordinates of the vehicle on each photograph were measured and transformed into ground coordinates used to calculate vehicle length, spacing, and speed. About 3400 vehicle trajectories were computed and filed in a data bank for subsequent analysis. Although no precise information is available as to the overall error derived from the operator, reduction system, and transformation methods, analysis of the trajectory data indicates the error in the computed position of a vehicle for any given frame averages about plus or minus 2.5 feet. /author/