The job: knowing the cost before the rate is agreed
How it is done today
In most small transport businesses, trip costing happens after the fact, if at all. Diesel is paid, tolls are paid, the driver is settled, and at month end the bank balance suggests whether it was a good month. Rates are quoted from what the market is doing and what was charged last time on that lane.
A trip calculator moves the arithmetic before the quote. It does not need to be precise to be useful. Getting fuel, tolls, allowances, empty running and a maintenance provision onto one row is enough to separate the lanes that pay from the ones that keep the trucks busy and the owner poor.