Public Transit vs Driving Calculator

Enter the one-way distance and days a week. The calculator doubles the distance and assumes 52 weeks, so 20 miles for five days is 10,400 miles a year. Reduce the days if you take holidays or work from home.

Enter the fare per ride and choose bus or rail. The fare is doubled for the return trip. If you buy a monthly pass, divide its price by the rides you actually take and enter that. At $3.00 a ride, rail costs $1,560 a year.

Enter your car's MPG, the gas price and the operating cost per mile: the maintenance, tyres and wear that rise with mileage. At 24 mpg and $3.50, fuel is about 14.6 cents a mile; adding $0.10 brings driving to $2,557, and rail saves $997 a year, or about $83 a month.

Read the emissions lines. The car emits 370 g per mile and rail 77 g, so the switch avoids 3.05 tonnes a year. Check the operating-cost input before trusting the saving: with it set to zero (fuel only), the same car costs $1,517 a year and rail becomes $43 more expensive than driving. The per-mile running cost, not the fuel, is what makes rail the cheaper option here.

Round-trip miles = one-way miles × 2. Annual miles = round-trip miles × days a week × 52. Days are capped at seven.

Annual transit cost = fare × 2 × days a week × 52.

Car cost a mile = gas price ÷ MPG + operating cost a mile. Annual driving cost = round-trip miles × days × 52 × car cost a mile. Annual savings = driving − transit, and monthly savings = annual savings ÷ 12.

Car emissions (g CO2 a mile) = 8,887 ÷ MPG. The 8,887 grams of CO2 per gallon of gasoline is the US Environmental Protection Agency's figure. The car is treated as carrying one person.

Transit emissions (g CO2 a passenger-mile): bus 431, rail 77. These are 0.95 lb and 0.17 lb converted to grams, the 2019 averages for transit buses and rail transit in the Congressional Budget Office report *Emissions of Carbon Dioxide in the Transportation Sector* (December 2022). Per passenger-kilometre they are about 268 g for bus and 48 g for rail, against 230 g for a 24 mpg car with one occupant.

CO2 avoided (tonnes a year) = (car g a mile − transit g a mile) × annual miles ÷ 1,000,000, floored at zero. When transit emits more than the car, the calculator shows 0.00 rather than a negative number.

Take a longer rural commute: 35 miles each way, five days a week, a $4.00 bus fare, against a more efficient 32 mpg car at $3.50 gas and $0.10 a mile.

On cost the bus wins comfortably. Transit is $2,080 a year; driving 18,200 miles costs $3,811, so the bus saves $1,731, about $144 a month. Longer commutes magnify the per-mile cost of driving while a flat fare stays flat.

On emissions the bus loses. The 32 mpg car emits 278 g a mile, well under the bus average of 431 g, so the calculator reports 0.00 tonnes avoided. At the average figure, riding the bus would add roughly 2.79 tonnes a year compared with driving alone.

Set against the urban rail example, the pattern is clear. Rail at 77 g beats any gasoline car on emissions. A car would need about 115 mpg to match it. The average bus only beats a car driven alone that gets less than about 20.6 mpg. Cost and emissions can point in opposite directions, and the calculator shows both rather than assuming transit wins each time.

A bus or train burns nearly the same fuel whether it carries five people or fifty, so its per-passenger figure is its total emissions divided by the riders on board. The CBO report makes the point with its own numbers: transit buses averaged 0.95 lb per passenger-mile in 2019, largely because they often ran well below capacity, while intercity buses (similar vehicles running fuller) averaged 0.15 lb, lower than rail transit. Double the riders on a bus and its per-passenger figure halves.

The car side has an occupancy assumption too. This calculator divides by one driver. CBO's average for personal vehicles, which reflects typical occupancy, was 0.47 lb (about 213 g) per passenger-mile. To model a two-person carpool, enter double your MPG: a 24 mpg car becomes 48, its per-person figure drops to 185 g, and the 20-mile rail commute still avoids 1.12 tonnes a year per person.

So the honest comparison is local. A crowded peak-hour bus can beat almost any car, an empty off-peak one can lose to a hybrid, and electric rail on a clean grid can do better than the national average. The averages here are a starting point, not a verdict on your route.

Included: fuel, and whatever you enter as a per-mile operating cost (maintenance, tyres, and mileage-related wear and depreciation).

Not included: insurance, registration, loan interest, parking, tolls, and the depreciation a car suffers with age even when parked. For a household that keeps the car regardless, leaving these out is correct, because switching commute mode doesn't remove them. For a household deciding whether it needs a second car at all, they are usually the biggest numbers, and the real saving from transit is larger than shown. Parking alone can outweigh the fuel on a downtown commute.

The emissions factors are national averages for 2019 and ignore your system's ridership, fleet and power source. The car figure is tailpipe CO2 from gasoline only: no upstream fuel production, no manufacturing, and no electric vehicles, which need a grid-intensity calculation instead. Time, reliability and the walk or drive to the station are not modelled, and they often decide the question more than cost does.

For a different way to cut commute emissions and cost, the ebike vs. car savings calculator covers short-to-moderate distances where neither transit nor driving is the obvious answer, and the eco commute & WFH calculator prices the trips you don't take at all on remote-work days. For an unassisted bike, the bike commute carbon and calorie calculator adds the calories burned to the emissions avoided. To see your car's baseline cost per mile in more detail before filling in the operating-cost input, use the fuel cost calculator. For the freight side of transport, the food miles calculator applies the same mode-matters-more-than-distance logic to shipping.