It is possible to specify route costs as a per-distance rate for each road type, by using the Road Costs dialog box. This is displayed by pressing Set Costs on the Road Parameters dialog box, or by pressing the Set Road Costs button on the Costs and Rate Tables dialog box. Note that the road costs are only used if the Type of rate table is set to Costs By Road Type. The dialog box looks like this:
Cost Units specifies the current cost units. These are "per" the current distance units (miles in the above example).
The default costs are all "1.00". To edit a road's cost, click on the cost's cell and type in a new value or use the spin buttons that will appear.