State and local departments of transportation (DOTs) increasingly deploy road detectors, such as inductive loops, to monitor congestion on their road networks. As deployment increases, the operating and maintenance cost associated with these detector systems will become issues for many state DOTs. Agencies will need to decide where to add new detectors and which detectors should continue receiving maintenance, given their resource constraints. For data collected from these sensors to remain meaningful, traffic data quality should not be adversely affected in these decisions. The needed traffic data quality depends on the data's intended purposes. An empirical study was conducted to address the impact of sensor spacing along freeway corridors on the computation of performance measures such as travel time index. The scenario that has the smallest sensor spacing (greater density of sensors) is considered to capture actual traffic conditions most closely. If sensor spacing is increased, how will the quality o...