(Off Hwy Truck Frame) I saw this huge engine on this trailer at the truck stop at the Princeton, IL exit of I80. I couldn’t get a straight-on shot because of the semi parked on the other side and there is a fence directly behind me on this side. The trailer has 3 sets of 3 axles and each axle has 2 duals. There are some hydraulic cylinders between the rear trucks that appeared to be used for steering. Photo 7-2-00. Description of the yellow item from a Caterpillar engineer: What you are looking at is rigid frame, off highway truck. The cab, front wheels, rear axle, and bed have been removed. The circles in the back are where the final drives bolt to the differential. This is a small truck, probably about 100 ton.