Not making the client pay specifically and separate for travel. It should cost them more to have you come over to their office. That way incentives are aligned. That way they'll book all weeks meetings in one day, instead of having you come over to their office every day.
And ensuring travel hours, despite being paid, are not working hours. Working on a train or plane is fine, if you feel like it. But it should be your choice, a courtesy. Not something they can expect. "I'll get that report 9:30 tomorrow. Tomorrow? But you still have two hours of travelling. Yes. Which is why I cannot finish it tonight."
And ensuring travel hours, despite being paid, are not working hours. Working on a train or plane is fine, if you feel like it. But it should be your choice, a courtesy. Not something they can expect. "I'll get that report 9:30 tomorrow. Tomorrow? But you still have two hours of travelling. Yes. Which is why I cannot finish it tonight."