The load history that railroad tank cars experience has a significant variable amplitude characteristic. Although previous efforts have been directed toward understanding baseline fatigue crack growth behavior of TC-128B steel as a function of material lot, orientation, and environment, little is known regarding how load interaction impacts crack growth behavior in a typical tank car steel. Load interaction occurs when the variable amplitude character of the loading results in crack growth that differs as a function of load history effects in the wake of the crack. The focus of this testing effort was to determine empirically how TC- 128B behaves under these types of simplified loading conditions. The data provided in this report links the constant amplitudeloading regime to the more complex variable amplitude-loading regime that tank cars experience during in-service use. The data can also be used as modeling guidelines to better understand the role of variable amplitude loading on TC-128B.