I am going to reply in different postings to your different replies/situations, but to Colleen;
to be clear, {what the employee does after the work day starts does not enter into this part of the question} ?your people are provided a vehicle to transport them from home to the same office, where they do all their paperwork, and begin and end each day's work? ?they start and stop work the same time and place every day, and from that place they provide an accounting of the time worked?
the % of that vehicles miles/expense used in that commute vs overall miles/expense, is an expense to the company, and a taxable benefit to the employee, in my opinion, otherwise (non taxable vehicles) would be a regular benefit in very many jobs, as a fine way to avoid federal taxes in the USA.
I think it may be a gross over-simplification to say it makes any difference if "the customer is not being billed for travel time". It seems to me that it does make a difference at "whose convenience" it is at.
The fact there is no external customer to bill, or the labor is "flat rated", or "extended warranty" does not make any difference, where the diff is, is in: is the employee expected to be at a location because it is where the employee wants to be, or because there is some "business reason" that the employer expects the employee to be at a particular location. In other words, does the employer pay for that same thing at some other hour of the day?
If Colleen includes travel in the calculations for flat rate charged for that work, and that work is done somewhere other than her shop, then she IS being paid for the travel, even if not separately broken out in the billing.
A second thing to think about, (again, IANL but I have worked all through this question a few times, from different angles, to try and figure a 'best practice') if this is -in fact- a benefit to the employee (and no greater benefit to the company, equal to a maid service paying for their taxi fare to the office) it may very well be a _taxable_ benefit, requiring considerable record keeping to separate the value of the truck and related expenses to/from the % of use as a benefit given the employee. ["Check with -your- tax attorney/CPA?] Along with the alternative of the company being liable for the expense of the techs tools in a break-in, [?ask -your- insurance agent to put it in writing?] if they are required or optioned to leave their trucks in the shop over night, as opposed to the tech's home owners insurance covering the tools while in his driveway.
You may also find, as one of the first steps down that road, (which will be an inventory of the techs tools which seems to run about 6 man hours per tech on company non billed/training time), what the replacement value of the techs tools are, which should engender an appreciation of how much a 'partner' in the business the techs really are, and how much of an investment they have made. I am not surprised if the replacement value exceeds 5 figures per tech.