Direct-fixation fastener systems of different designs and characteristics are used by transit agencies to secure rails to underlying structures. When adequately suited for the specific application, these fastener systems enhance track quality, improve passenger comfort, and reduce maintenance requirements by maintaining proper gage and alignment, controlling longitudinal rail movement, providing resilience, assuring electrical isolation, and attenuating noise and vibrations. However, experience has shown that direct-fixation tracks are not always trouble-free and that problems exist to varying degrees with some direct-fixation fastener systems and their applications.

Several analytical and experimental investigations have been conducted to understand the mechanisms involved in rail/vehicle interaction and to identify means for improving track-structure performance. These investigations indicated that fastener stiffness, vehicle suspension, track geometry, environmental factors, and operating conditions are among the items that affect track-structure performance. These studies, however, did not provide conclusive information to alleviate direct-fixation fastener problems. Thus, research was needed to provide a better understanding of the influence of track, vehicle, and operating characteristics on the performance of the direct-fixation track structure as an interactive system, and to develop guidelines with associated analytical methodologies to assist transit agencies in selecting the appropriate options for specific situations.

The objectives of this research were to (1) develop analytical methods to improve direct-fixation track-structure performance through the identification and use of compatible vehicle and track-structure characteristics and (2) provide guidelines that will assist transit agencies in evaluating and selecting direct-fixation fastener systems. The research was limited to the performance of direct-fixation track structure on light and heavy rail-transit systems.

Status: The design guidelines have been published as CRP-CD-3, "Performance of Direct-Fixation Track Software: Design Guidelines and Software."