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.

The description also states that it increases the "boss range" although I could see no detectable change at level 1.

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.