If we assume an average speed of 30mph, that's at least 120 miles weekly, which at $0.50 per mile (the cost of car ownership according to the IRS) is $60/week. Over 50 work weeks, that's $3,000 annually (after taxes) in commuting costs.

There's also an opportunity cost -- if we assume a wage of $15/hr, then 4/hrs week * 50 weeks is 200 hours annually, or $3,000/hr annually.

So the "average" commute in the US costs $6,000.