Previous research in Canada, Finland, Sweden and the United States has indicated that daytime running lights (DRLs) - vehicle lights that are on during daylight hours - can reduce the frequency of daytime multiple-vehicle crashes. In this study, over 2, 000 passenger cars, vans, and pickup trucks in three fleets were modified to operate with DRLs. An inexpensive relay was installed on these vehicles to automatically turn on their front parking lights and rear tail lights with vehicle ignition. In addition, bulbs with substantially higher intensity minor filaments were installed in the front parking lights. The crash experience of these vehicles was compared to similar but unmodified vehicles in the fleets. Overall, the proportion of multiple-vehicle crashes relevant to DRLs that occurred during daytime hours was seven percent lower for the vehicles equipped with DRLs.