Index | Table of contents | Technical Report | Executive Summary | Background | Rear Window Defrogger and Wiper Information | State Crash Data | Analysis Databases | Analysis Method | Hypotheses | Conclusions | Appendix A
Background
FMVSS 103 requires all passenger cars, multipurpose passenger vehicles, trucks and buses manufactured on or after January 1, 1968, to have windshield defrosting and defogging systems. However, rear window defrosting and defogging systems, hereafter referred to as rear window defoggers, are not required. Rear window defoggers became available as optional or standard equipment in most cars during the 1970's or 1980's and are popular with consumers. Rear window defoggers allow the driver to see through the rear window under adverse weather conditions. Clear vision is especially important when the driver wants to back up or change lanes.
FMVSS 104 requires all passenger cars, multipurpose passenger vehicles, trucks and buses manufactured on or after January 1, 1968, to have windshield wiping and washing systems. Similar to rear window defoggers, rear-window wiping and washing systems are not required. Rear window wipers have been installed on a smaller group of vehicles for even better vision.
This study assesses the effectiveness of rear window defoggers in reducing crashes in which a driver is backing up, changing lanes, or performing other tasks that would be facilitated by vision through the rear window. Typically, studies to assess the effectiveness of a vehicle safety standard consist of an analysis of crash data that compare the experience of vehicles that meet the safety standard to those that do not meet the standard. For most evaluation studies, we can identify exactly what vehicles were equipped with a safety technology, and which ones were not, based on the model year (e.g., before/after a standard’s effective date, or before/after a date when the technology became standard equipment) or dedicated VIN characters (e.g., air bags), or specific mention in the crash data (e.g., child safety seats). However, rear-window defoggers and wipers have never been required safety equipment and were offered as optional equipment, for many years, on quite a few make-models. The presence of rear-window defoggers and wipers generally cannot be deduced from the first 12 characters of the VIN, and it is rarely (if ever) mentioned on crash data files. Therefore, it is necessary to obtain information on the proportion of vehicles with rear-window defoggers or wipers from another source.