As border communities grow and increase in economic integration, measurement of queuing delays for passenger vehicles at border crossings becomes more important. At the San Ysidro, California, Port of Entry, recent research has included development and testing of techniques for measuring queuing delays. These measurements were intended to be used as traveler information and for monitoring ... [Show full abstract] compliance with traffic management objectives. Techniques tested at San Ysidro involved indirect measurement of queue sizes and wait times. These measurements displayed problems with both accuracy and precision. Problems with accuracy appear to be related to data quality and probably can be overcome by better data collection methods. Problems with precision are an inherent feature of indirect measurement techniques and are the result of the variability of queue density and vehicle-processing rates about their mean values. Monitoring efforts are intended to track changes in delay over long periods of time and are relatively insensitive to the precision of the measurements. Traveler information services, however, depend on the ability to closely approximate the delays experienced by individual travelers and are thus highly sensitive to precision. Consequently, the emphasis on measuring queuing delays at border crossings should normally be on monitoring rather than on traveler information.