Traffic Information Service (TIS) is a Mode S data link application being developed for use by general aviation (GA) pilots. Its purpose is to provide a low-cost means of assisting the pilot in visual acquisition of nearby aircraft. The service provides two functions: traffic alerting and threat assessment. These functions are also performed by the Traffic Alert and Collision Avoidance System (TCAS). The purpose of this report is to evaluate the effectiveness and safety of TIS in relation to that of TCAS I. The analysis begins with a conceptual review of Andrews' statistical model of visual acquisition. Next, the surveillance systems and threat-detection logic of TIS and TCAS I are reviewed. Results of a Monte Carlo simulation that modeled the threat-assessment performance of TCAS I and TIS are also presented. The analysis supports the conclusion that, because of the high degree of similarity between TIS and TCAS I, TIS is a safe and effective means of assisting the pilot in visual acquisition of air traffic.