The effects of an automated Speed Photo-radar Enforcement (SPE) system on the speed of vehicles in highway work zones were evaluated in this study. The SPE effects were also compared to other speed management treatments, including speed display trailers, police presence (with the patrol emergency lights on and off), and the combination of speed display trailer and police presence. Three datasets were collected in two work zones and the effects were studied at the location of the treatment and also at a location about 1.5 miles downstream in the work zone (spatial effects). The halo effects (temporal effects) of police presence and SPE, after they left the work zone, were also analyzed. Results are presented separately for cars and trucks in free-flow and in the general traffic stream in the median and shoulder lanes.