At the last Company, I charged normal Hourly Rate for Travel Time when one-way distance exceeded 30 Miles.
Fuel and PerDiem (plus other out-of pocket expenses) were reimbursed according to job number and pay period (pay check / time card).
Sometimes PerDiem allotments were issued on a check and given to the traveling person prior to out of town work (central or northern California travel). This included Motel and personal expenses (excluing fuel) anticipated for the period of travel (per day).
What was not used got reimbursed to the company, what was paid out by the employee got reimbursed by the company.
Receipts were included with time cards to verify expenses.
Since this was working very well and made too much sense, it of course had to be ended!
The key clown involved with this great idea was the same joker responsible for numerous other dumb things (like writing a book on "What NOT to do as a Prog. Mgr."!).
This became known as "Curtis' Brainchild #100".
Man I am sooooooooooo glad to be away from that bonehead!