The reconstruction of collisions involving trailer side underride by passenger vehicles is complex and challenging. A detailed analysis of the passenger vehicle's post-impact damage is required to evaluate the collision phase and ultimately to determine its impact speed. The research of trailer side underride crashes currently available to the accident reconstructionist, however, is relatively limited.This paper presents the results of controlled underride crash testing performed on eighteen instrumented low profile and high profile passenger vehicles colliding with the sides of commercial trailers at speeds ranging from 15 to 39 miles per hour. The pre and post-collision geometries of each test vehicle were documented with three-dimensional measurements to accurately quantify the collision damages sustained and relate them to the vehicle's kinetic energy and impact speed. The vehicle and trailer interactions during the collision phase of the tests are discussed with emphasis on the implications for accident reconstruction. The test results indicate that there exists a correlation between the kinetic energy of the colliding vehicle and the volume of the resulting intrusion damage, or crush zone. Additional underride crash tests performed by other researchers are integrated into the data set and the overall results further support the correlation found in this study. This paper presents a new method to derive relatively accurate speed estimates of both low profile and high profile passenger vehicles involved in trailer side underride collisions.