Are you driving? In the US the federal rate is now .55 cents per mile. http://www.irs.gov/uac/IRS-Announces...-Mileage-Rates
When I drive to my client's office, I charge .55 cents a mile plus my hourly rate. If I take the train, I charge the hourly rate only. My time is valuable, just like my skills. And if I'm spending my time getting to a client, it's time I'm not using to do work for other clients.
Either way, you might want to have this conversation with your client before you invoice them. If you guys aren't on the same page about this you could lose trust and credibility, which could equal less work in the future.
Hope this helps...