Given the increased emphasis on transportation system operations, transportation agencies require effective operations performance measures. The purpose of the present research effort was to develop and explore the utility of a simple system operations performance measure that meets the following criteria: (a) it is measurable given current sensor deployment, (b) it is understandable to a wide range of individuals, (c) it is applicable on different functional classes of roadways, (d) it is scalable from the lane level up to a regional or statewide measure, and (e) it is independent of major assumptions or estimation techniques. The measure proposed and explored in this paper, the speed index, can be defined as the volume-weighted percentage of the speed limit at which a roadway location, zone, corridor, or even a region operated for a given time period. This measure was demonstrated to be effective in supporting numerous operations analysis activities, including an analysis of seasonal variations in traffic and an in-depth analysis of a single incident's impact on regional conditions. On the basis of the case study presented, it is concluded that the speed index is a viable measure that can be used to support state operations programs.