This paper presents an overview of currently ongoing research by the National Highway Traffic Safety Administration (NHTSA) in the area of light vehicle (passenger cars and light trucks) Antilock Brake Systems (ABS). This paper serves as a lead-in to other papers that will be presented during this session.Several statistical crash data studies have found there to be little or no net safety benefit from the implementation of four-wheel ABS on passenger automobiles. Typically, these studies have found ABS to be associated with: 1. A statistically significant decrease in multi-vehicle crashes. 2. A statistically significant decrease in fatal pedestrian strikes. 3. A statistically significant increase in single-vehicle road departure crashes.The safety disbenefit due to the third finding approximately cancels the safety benefits from the first two findings.The third finding from the statistical crash data studies, the increase in fatal single-vehicle crashes associated with the implementation of ABS on passenger automobiles, is quite surprising. Prior to the widespread introduction of ABS, safety experts expected that adding ABS would decrease the frequency of single-vehicle crashes, not increase the frequency. Interestingly, such a decrease is exactly what was found by crash data studies that have looked at the effects of adding rear-wheel only ABS to light trucks.NHTSA wants to find out why the addition of ABS has been associated with an increase in the frequency of single-vehicle crashes for passenger automobiles. NHTSA hopes that once the reasons for this increase are known, countermeasures can be developed so that ABS will produce its expected overall safety benefit for passenger automobiles.A list of possible reasons why ABS is not producing its anticipated safety benefits is presented. The paper then gives a summary of the research tasks being performed to investigate each of these possible reasons.