When an attempt to attach a shipment leg with a committed tractor or trailer equipment type to a load is made, the system will check that the resulting tariff/service/equipment type combination is a valid one.
Loads that might be combined on a trip are validated in a similar way. Not all loads on a trip have to have the same trailer equipment type, but the tariff/service combination for the carrier and service assigned to the trip must have all the tractor and trailer equipment types for all the loads on the trip defined for it. The only situation where all loads on the trip must have the same trailer equipment type is when the carrier assigned to the trip cannot perform non-live loading or unloading.