The two CONUS rail clearance diagrams or envelopes of interest are the Association of American Railroads (AAR) Outline Diagram for Single Loads, without End Overhang on Open-top Cars, and the DOD Clearance Profile for the Strategic Rail Corridor Network (STRACNET).
For generally unrestricted movement in North America, the height and width of a loaded railcar shall remain within the limitations of the
AAR clearance diagram or envelope. Loads wider than the flatcar, or combined load plus flatcar heights greater than 15 feet 1 inch above the top of the rails, are considered "dimensional loads." All involved railroad companies will perform clearance checks on "dimensional loads" for the entire distance of shipment before such shipments will begin. Clearance checks may delay rail transport because they are performed during normal working hours.
When railcars are requested from a railroad company on short notice, the railroad company will furnish what is readily available. Deck heights of flatcars can vary. For these reasons, unrestricted rail transport is based on a standard worst-case flatcar deck height of 51 inches. When unrestricted North American rail transport is a requirement, new items of equipment shall be designed such that the item outline is within the
AAR diagram or envelope when placed on a 51-inch-high flatcar.
The DOD STRACNET connects all major Army installations, depots and ports of embarkation. The
DOD STRACNET clearance profile accommodates 86% of DOD types of equipment and 99% of individual pieces of equipment in the DOD inventory. However, it's only valid for selected routes and sometimes only at severely restricted speeds.
Designing exclusively to the
DOD STRACNET profile may result in deployment delays.
Typical CONUS flatcar physical characteristics may be found in MIL-STD-1366 Transportability Criteria (1.58 MB). Data sheet on typical CONUS flatcar physical characteristics may be downloaded, US Flatcar Reference US Flatcar Reference (384 KB).
In addition to meeting CONUS rail clearance diagrams, the AAR requires that military vehicles that will be secured to flatcars for rail transport must also meet the rail impact test requirements outlined in MIL-STD-810, test method 526. This testing simulates "rail humping operations" that could occur during the life of the rail transport of the vehicle. If during rail impact testing a vehicle requires securement that deviates from the general rules or a specific figure in the AAR's Open Top Loading Rules (OTLRs), those testing results must be submitted to the AAR OTLR committee for review and possible generation of a new figure within the OTLRs. If you desire a copy of the Section 6 of the OTLRs that covers Military Equipment and Materiel please contact
Why nylon tiedowns are not acceptable for CONUS transport.