RAWLINS — The world’s largest operating steam locomotive, 600-ton Union Pacific Big Boy No. 4014, derailed Thursday afternoon as it entered the yard in Rawlins while on the return leg of its journey to celebrate No. 4014’s restoration and the 150th anniversary of the Golden Spike.

The Big Boy, 4-8-4 No. 844, and 12 passenger cars in UP’s heritage fleet are due in Laramie at 12:45 this afternoon, but there is no word as to whether the derailment and delay will affect Big Boy’s schedule.

Trains.com reported that driver axles Nos. 2 and 3 on the second engine of the articulated locomotive fell into the gauge as the engine entered the yard at the Washington Street underpass in Rawlins. The accident took place at about 2:15 p.m.

The engine was moving slowly when the drivers came off the rails. The front engine, front truck, rear truck, and driver axles Nos. 1 and 4 all remained on the rails. The UP steam crew worked with local track forces to fix the track under the engine and bring the locomotive’s 68-inch drivers back onto the rails, which they accomplished about 5:20 p.m.