what does it cost to operate a road tractor just the tractor?
their is no general answer to that because their are to many factors
As said above way to many factors. Depending on what you are pulling, the terrain will dictate fuel usages. Fuel prices, operator wages, workmens comp etc will also vary greatly.
Rather than cost per hour it may be wiser to look at cost per mile.
here is a help sheet / cost /mile calculator to figure out what it costs to run a truck http://www.truckershelper.com/operationscost.php