The Math and Mystery Behind Calculating How Much People Drive

Sadly, there currently isn't very good data on how much your average Bay Area or California resident drives each year. 

That's why TransForm is sponsoring AB 1135.  AB 1135 would require drivers to record their odometer reading every year when renewing their vehicle's registration.  This would allow California to finally be able to accurately track the amount of vehicle miles that Californians drive each year. 

In the meantime, we wanted to have a benchmark so that at the end of the Car-Free Challenge, we could compare how much Challengers drove with how much your average person drove.

The number we have chosen to use during the Challenge is 18 miles per day per participant, or 540 miles per month.  This is a conservative number.  Here's how we picked that number; plus another number of 32 miles per Bay Area driver per day that is sometimes used, too.

Claim: The average Bay Area resident drives 18 miles per day.

The Math:

85%* of total Bay Area vehicle miles traveled (VMT) / Bay Area population.

*15% is the widely accepted percentage of daily VMT that is commercial use that should not included in personal or individual driving totals.

Claim: The average Bay Area driver drives 32 miles per day.

The Math:

Total Bay Area vehicle miles traveled (VMT) / total licensed Bay Area residents.

Sources:

Bay Area VMT & Population: http://www.mtc.ca.gov/maps_and_data/datamart/stats/vmt.htm

Bay Area Driver Licenses: http://dmv.ca.gov/about/profile/dl_outs_by_county.pdf