During the past decade, the international community has witnessed several attacks on forms of mass transportation such as train stations and subways. The Department of Homeland Security requested that we develop methods to assess the security of mass transit in order to mitigate the vulnerability of the nation's public transportation systems. We present a methodology to quantify the impact of imposing screening on mass transit, which considers both security and delays incurred on the traveling public. We demonstrate the approach through a case study, the Fairfield Metro Station in Fairfield, Connecticut. Our results indicate that rigorous aviation-style screening will slow the flow of passengers drastically. We also show how to use the approach to identify where faster screening technologies can improve passenger throughput while ensuring security. The approach can thus be used to identify areas where investments in technology improvement would most effectively enhance security and convenience.