Clients often don’t want to pay for many things that you have to do to help them. Traveling is a classic issue, but it can also include research, reporting, and so on. Thing is, there is a way for both sides to be happy if you use the “magic” of the billable hour.
It’s not always called this, but a billable hour is a unit of measurement often used in professional services billing, nominally to record and charge the time spent working on a particular client’s problem, for the purpose of constructing a bill.
If I wanted to mistify it further, I’d call them “value-illustrating” hours: the part of work that the client is able to trust, respect, or recognize as necessary building blocks for the value they expect.
If I wanted to clear it up, I’d call them “load-bearing” hours: the part of work that needs to carry enough “weight” of the client’s expectations to enable the whole of your work to be adequately compensated.
Not everything you need to charge for needs to be on the bill explicitly. If you need to do 160 hours of work to do a project but the client is likely to approve just 100 of them, make sure your offer leaves out the undesirable hours but is also 60% higher and everybody gets to feel like a winner.
As long as you and your client are happy with the deal, no law says that what the bill says they paid for and what you feel compensated for have to be an exact match.