We add together all vehicle costs for the year for all vehicles  including fuel, maintenance, depreciation, leases, etc. everything vehicle related. Divide that by the number of vehicles, divided by the number of working days in the year (approx 255), divided by our average hours worked per day for the typical driver (We use 10 hours). This gives an hourly rate per driver to cost to the jobs.

As we post hours to the job, every hour that the driver has on the job automatically gets this amount added to the job costing. We use the same number for estimating. It is easy with computerized job costing. If you aren't computerized you could try using a daily or weekly rate

We have seen different ways of allocatiing vehicle and other equipment costs to projects.  One common way to is to create rates including ownership and operating costs and apply them by the hour or some other measure of time.  The number of hours and the distribution of those hours often mirror that of the foreman or operator.  Some will cap the hours for the vehicle by day, week, or month, others might not.

Still others, will apply ownership and operating costs by the mile.  For operators that are on fixed projects the distribution might not be too complicated, however, for operators that move from project to project it may be more difficult to record the allocation properly, but it can be done.

We use  fuel cards which provide reporting for each week by driver id.  We allocate the fuel costs based on hours worked. Not perfect, but we think its reasonable.  We used to have drivers code every fuel receipt.  That was very time consuming and certainly not a perfect match of costs to jobs either.