## How We Calculate Our Numbers

The Car-Free Diet calculator is designed to provide a general picture of how replacing one or more driving trips each week with biking, walking, transit or telework can help you spend less money, burn more calories, and reduce the amount of carbon dioxide you emit into the atmosphere. It is NOT meant to produce scientifically accurate calculations. The numbers provided are rough estimates only and may be different from your actual numbers — they do, however, reflect overarching, general truths about how going car free can affect your life.

### Money

- We calculate your cost of driving a car by adding together the following amounts:
- The average cost of car ownership, maintenance and tire purchases (47¢/mile for a medium-sized sedan driving 12,000 miles a year - pacebus.com/sub/vanpool/cost_of_driving.asp)
- The price of gas per gallon you enter, divided by the miles per gallon fuel efficiency of the car you enter (according to the Environmental Protection Agency)
- Any amounts you enter for tolls or parking

We calculate your costs for using car-free transportation options using the following sources:

- Bike — average cost of bicycle, accessories, clothing, shoes and maintenance ($350/year - from BicycleUniverse.info), divided by the average number of miles biked (3000 miles/year — from the Transportation Research Board)
- Walk — average cost of clothing, shoes and miscellaneous items ($120/year), divided by the average number of miles walked (1500 miles — from the Mayo Clinic)
- Telework — average cost of teleworking is $0 (typical telework programs cost nothing to employees — teleworkva.org)
- Transit — EITHER the amount you enter when asked "If you rode transit, how much would this trip cost?" OR the average cost of a transit trip in Arlington ($3.25 — commuterpage.com) if you check "I don't know"

### Environment

We calculate how many pounds of carbon dioxide (CO2) emissions your car produces by using the following formula:

- The number of pounds of CO2 emitted while burning one gallon of gasoline (19.564 lbs — from the U.S. Department of Energy), divided by the miles per gallon fuel efficiency of the car you enter (advertised estimates are from the Environmental Protection Agency)

We calculate the CO2 emissions for car-free transportation options using the following sources:

- Bike, Walk & Telework — no CO2 emissions other than from exhaling (see below)
- Transit — the number of pounds of CO2 emitted while burning one gallon of gasoline (19.564 lbs — from the U.S. Department of Energy), divided by the miles per gallon fuel efficiency of an average bus (10 mpg — from the Journal of Public Transportation — PDF, Adobe Reader required) divided by the average number of bus passengers at any given time (10 passengers — from the Journal of Public Transportation — PDF, Adobe Reader required)

Because human beings emit a small amount of carbon dioxide while exhaling, we also add this amount (0.00002 lbs/minute/lb of body weight while walking or biking, 0.00001 lbs/minute/lb of body weight while driving, riding transit or teleworking — *citation needed*) to each mode of transportation's total.

### Health

- We calculate how many calories you burn while driving your car using the following:
- 0.012 calories burned/minute/lb of body weight (coolnurse.com)
- We calculate how many calories you burn while taking car-free transportation options using the following:
- Bike — 0.061 calories burned/minute/lb of body weight (while biking at 12 mph — nutristrategy.com)
- Walk — 0.042 calories burned/minute/lb of body weight (while walking at 4 mph — nutristrategy.com)
- Telework — 0.008 calories burned/minute/lb of body weight (while sitting — coolnurse.com)
- Transit — 0.042 calories burned/minute/lb of body weight (while walking an estimated 0.5 miles to/from transit — nutristrategy.com) plus 0.008 calories burned/minute/lb of body weight (while sitting during the ride — coolnurse.com)

Because the number of calories burned is calculated per minute (not per mile, like cost and CO2 emissions), we use travel time to determine this value. We use the travel time you enter to calculate the number of calories burned while driving. For car-free travel times, we use the following estimates:

- Bike — 5 minutes per mile
- Walk — 15 minutes per mile
- Telework — no travel time

Transit — same travel time as driving (we assume that transit in general is faster, but due to frequent stopping and starting, its overall travel time is similar to that of driving)

### Default Values

If you choose not to answer some calculator questions, we automatically use the following defaults:

- Body Weight: 140 lbs
- Vehicle Miles Per Gallon: 21 mpg
- Trip Distance: 9.5 mi
- Trip Time: 31 min
- Toll Costs: $0
- Parking Costs: $0
- Transit Trip Cost: $3.25