In this paper, we present the challenges in gathering network traffic information from an emergency response network, discuss the non-invasive traffic sensing and analyzing infrastructure that we created and used for a real-world application, and present some of the performance observations made using our infrastructure. Network performance measurement and analysis is a challenging task for a large-scale emergency response network. We developed an infrastructure for non-invasive traffic monitoring that requires neither modifications to nor knowledge about the production emergency response network. Our non-invasive network measurement infrastructure was used for real-world emergency response drills such as the Golden Eagle drill conducted at California State University, San Marcos in May 2010. Performance observations obtained from our system show that non-invasive traffic monitoring is a scalable, efficient, and viable method for large-scale network monitoring and performance measurement. © 2011 IEEE.