The haulage firm decreases transportation costs for purchase requests. At level 1 costs decrease from 15% to 14%, so it is likely that the costs decrease by 1% per level of the haulage firm.
Every upgrade of haulage firm also increases the boss range. It is not stated how much the boss range radius exactly increases per upgrade, but the increase is approximately 5 - 10 metres.
At level 5 it allows the automatic collection of all lost freight in boss range and has a % chance of automatically collecting lost freight within the normal interaction range.