$6/hr sounds a bit low; actual costs are probably higher.
The IRS standard mileage rate (the amount you can deduct from your taxes for each mile driven) is $0.58/mi (https://www.irs.gov/tax-professionals/standard-mileage-rates)
$6/hr operating costs means the driver is driving a max of ~10mi/hour, if costs to operate are in line with IRS guidelines.