My commute is 25 km one-way. (just under 16 miles)
In the mornings, my husband and I drive together. At night, because I work later, and he has to pick the kids up from daycare, he drives alone, and I take the bus, which is $4.18 one-way (I use a Presto card, so I know exactly how much I spend on transit).
While the distance would be bike-able for an avid cyclist, I'm not willing to do it because it would cut into the very limited time I can spend with the kids (i.e., I would get home at least a half hour later), and then I wouldn't be able to get dinner on the table in time.
On paper, there is likely no justification for choosing to live so far from work. With the amount I spent on my home, I could probably find a livable space very close to work. My office is in a very desirable neighbourhood (which is expensive though, so what I could afford in this area would be pretty tiny and possibly in need of very expensive repair).
My justification is entirely psychological - I love living in the country, being surrounded by trees and nature and having privacy around me.
Our monthly transportation-related costs (including gas, insurance, and my bus fares and any parking costs) seem to be averaging around $400. We put a lot of kilometres on the car; partially due to the commute, but also due to my husband's twice-weekly hockey (the rinks change but usually are between 20 and 30 km away; he's been playing with the same guys for 10 years though and I'm certainly not going to ask him to stop and find a closer arena), and the fact that we often visit family out of town (the last three months have us going to Toronto twice and Pembroke twice).
When I think about it, it does seem a bit high, considering the vehicle is efficient and paid off. Of the money we've spent over the last three months, $831 has been on fuel, so I guess that works out to an average of about $63/week on gas (again though, including road trips).
I'm trying to be more mindful of car trips though. Fewer trips to the store = fewer kilometres on the car in general.