Technology Digests / Bi-Level Autorack: Top Deck Loading Test

TD26-011

May 28, 2026
Authors
  • Stan Gurule
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Key Findings

  • Autorack top-only loading scenarios have raised performance questions. Modeling investigations for combined center-of-gravity (CG) loading scenarios are all at least 3 inches below the 98-inch AAR limit and most do not exceed 89 inches. For this test, the CG for the top-loaded car was 86.1 inches, and the CG for the fully loaded car was 83.9 inches.
  • All tested load scenarios met Chapter 11 requirements up to 65 mph. The full load and top load scenarios met requirements up to 70 mph.
  • Operating bi-level autoracks with cars only on the upper deck generally provided performance similar to other load scenarios. The exception was spiral entry where the top load performs more poorly than the other load scenarios yet still performed well within Chapter 11 criteria.
  • Additional guidance suggests monitoring CG limits, noting that future loading patterns exceeding 90 inches should undergo further research.

Bi-Level Autorack: Top Deck Loading Test

In November 2025, MxV Rail conducted autorack loading testing at the request of the Association of American Railroads (AAR) Mechanical Committee and in consultation with the AAR Research Committee. The AAR Equipment Engineering Committee (EEC) Autorack Loading Task Force has been investigating the performance of a top-only loading scenario of a bi-level autorack. This Technology Digest describes the MxV Rail team’s evaluation of the autorack in three load conditions (empty, top load, and full load). Cutaway image of tall vans on the upper deck. Source: Greenbrier The AAR Manual of Standards and Recommended Practices (MSRP) Section C-II, Chapter 11 provided the testing regimes including Dynamic Curve, Limiting Spiral, Pitch & Bounce, and Twist & Roll.1 This testing was performed under the AAR Strategic Research Initiatives (SRI) program and with cooperation and support from Greenbrier, TTX, and Ford Motor Company. INTRODUCTION  An EEC Autorack Loading Task Force…