Conventional speed studies can be used to evaluate the effects of various aspects of highway design and traffic control on the speeds at which drivers choose to travel. Typical parameters examined are mean speeds, 85th percentile speeds, and speed variation indicated by standard deviation or mode. More detailed studies have been conducted by using manual techniques and specialized equipment to generate vehicle-specific speed profiles. A useful technique, called vehicle tracing, allows data from common automatic traffic recorders to be used to generate such profiles automatically. The availability of these profiles opens new avenues of analysis that ultimately promote safer highway design and traffic-control practices. This technique is discussed, and its benefits are illustrated through a case study--an evaluation of optical speed bars, an innovative technique for slowing traffic in highway work zones.