As a precursor to the present research, Hanowski et al. [FHWA Report no. FHWA-MC-98-029. Office of Motor Carriers, Federal Highway Administration, Washington, DC, 1998] conducted a series of focus groups in which local/short haul (L/SH) drivers provided their perspective on safety issues, including fatigue, in their industry. As a follow-up to the Hanowski et al. work, the effort presented here consisted of an on-road field study where in-service L/SH trucks were instrumented with data collection equipment. Two L/SH trucking companies and 42 L/SH drivers participated in this research. The analyses focused on determining if fatigue is an issue in L/SH operations. Of primary interest were critical incidents (near-crashes) where L/SH drivers were judged to be at fault. The results of the analyses indicated that fatigue was present immediately prior to driver involvement in at-fault critical incidents. Though it is difficult to determine with certainty why fatigue was present, the results suggest that drivers' off-hours behavior likely played a significant role in the fatigue experienced on the job. Another key finding of this research is that a small percentage of drivers were responsible for a majority of the critical incidents. This finding suggests that driver selection and monitoring could potentially improve safety in L/SH operations.