Ballastless track (i.e. slab track) systems are used extensively in passenger rail applications for improved track stability, alignment control, vibration, and life cycle cost (LCC) benefits. These systems regularly rely on Direct Fixation (DF) fasteners to connect the rail to the structure. Field performance observations have indicated that even under similar track geometry and train operating conditions, the DF fasteners useful life varies widely. Meanwhile, a review of literature reveals that there is limited prior research to guide optimization of DF fastener designs for heavy rail transit. Therefore, researchers at the University of Illinois at Urbana-Champaign (UIUC) conducted a field investigation at three sites on a United States legacy heavy rail transit system to quantify wheel-rail interface loading demands and DF fastener response. Track response variance across similar track geometry was found. Wheel loads ranged between 2.7 to 18.2 kip (12.0 to 81.0 kN) and 0.9 to 12.4 kip (4.0 to 55.2 kN) for vertical and lateral loads, respectively. Lateral rail head displacements ranged between −0.05 to 0.16 inches (−1.27 to 4.06 mm) while dynamic lateral stiffness ranged from 42 to 62 kip/in. (7.3 to 10.8 kN/mm), indicating a low stiffness ratio for the DF fastener studied. Differences in behavior are attributed to dynamic vehicle-track interaction, the relationship between balanced and operating speeds, and differences in track gauge between sites. A comparison of vertical loading results with two additional heavy rail transit agencies shows Burr distributions that accurately represent the loading demands. Results from this study provide quantitative information that can be leveraged to improve heavy rail transit DF fastening system design and development of representative design validation testing protocols.

无轨道（即平板轨道）系统广泛用于客运铁路应用中，以提高轨道稳定性，对准控制，振动和生命周期成本（LCC）的好处。这些系统通常依靠直接固定（DF）紧固件将导轨连接到结构。现场性能观察表明，即使在类似的轨道几何形状和火车运行条件下，DF紧固件的使用寿命也会有很大差异。同时，对文献的回顾表明，在用于重型轨道交通的DF扣件设计优化的指导方面，现有研究很少。因此，伊利诺伊大学香槟分校（UIUC）的研究人员在美国传统重型轨道交通系统的三个站点进行了现场调查，以量化轮轨接口的载荷需求和DF紧固件的响应。发现了类似轨道几何形状的轨道响应方差。对于垂直和横向载荷，车轮载荷分别在2.7至18.2 kip（12.0至81.0 kN）和0.9至12.4 kip（4.0至55.2 kN）之间。轨头的横向位移范围为-0.05至0.16英寸（-1.27至4.06 mm），而动态侧向刚度范围为42至62 kip / in。（7.3至10.8 kN / mm），表明所研究的DF紧固件的刚度比低。行为上的差异归因于动态的车辆-轨道交互作用，平衡和运行速度之间的关系以及站点之间的轨距差异。将垂直荷载结果与另外两个重型铁路运输机构进行的比较显示，伯尔分布准确地代表了荷载需求。