Question about item (truck) size/spacing?

In CT, it seems as though trucks register with the same length. So the spacing between 2 bobtails would be the same as the spacing between two trucks with containers if I used a spacing value of 1 and "item size" as my spacing rule. Is there a way to somehow change the spacing on a conveyor based on the itemtype? Or give an item type a unique length when it enters the conveyor?

The size of an item (the truck in this case) is shown as a yellow box when you click on it. The 3d shape of the truck only takes up part of the entire size of the truck. I assume this is for better visualization with chassis and containers, turning on network nodes, and various other reasons in the yard.

As you noticed, this presents a problem on roads in the gate. You can use triggers to change the size of the truck before it enters a road. You have to also change the offsets so that the 3d shape is the correct size as well. Attached is a model that shows how to do this. The code is OnExit of GateQueue9. There is also code OnExit of GateRoad9 that sets the size back to what it originally was. You should do this before sending the truck to the yard.

Thanks, Phil, for your solution. I wasn't sure which shape factors to change, but you nailed it.