As I have shared before, I drive a hybrid hatchback, a 2015 Toyota Prius. To reduce my carbon footprint, I try to walk or scoot for many of my shorter trips, and I also check bus schedules for medium trips, like to a coffee shop in another neighborhood. It can be very frustrating, even living Downtown, when the estimated trip time for driving is 12 minutes and taking the bus may be 40 minutes with transfers.
In an unabashedly self-serving endeavor, I asked the internet, what is the carbon impact of driving anyway compared to the humble bus?
There are four popular powertrains for buses on the road today: diesel, diesel-electric hybrid, natural gas, and battery electric. According to the Union of Concerned Scientists, the carbon-equivalent emissions of these powertrains on a standard bus are 2,680 grams CO2e per mile for diesel, 2,212 for diesel-electric hybrid, 2,364 for natural gas, and 1,289 for battery electric in Minnesota, with our electricity generation mix. The national average for battery electric is 1,078 grams CO2e per mile.
My Toyota Prius over the past 30,000 miles or so has run at a fuel efficiency of 45 miles per gallon. When we convert this to emissions per mile with the EPA standard of 8,887 grams of CO2 per gallon of gasoline, we get about 197 grams CO2e per mile.
If we divide the bus emissions by the hybrid hatchback emissions, we can see that buses are not always more emissions-efficient. For diesel, it takes 13.6 riders to reach equivalency. For diesel-electric hybrid, it’s 11.2 riders. For natural gas, it’s 12.0 riders. And for battery electric, it’s 6.5 riders.
This basic analysis does not take into account route efficiency, where passenger cars are taking the more direct route than bus transfers. It also does not take into account the carbon footprint of having a driver. It is hard to calculate the carbon footprint of the average bus driver or rideshare driver, so if your Uber driver drives a Chevy Volt, it’s no guarantee that this has a smaller carbon impact than taking the bus.
These numbers do point to the future. Carbon emissions are tied to budget costs, and electric vehicles have lower running costs generally than diesel or gasoline motor equivalents. Maybe in the future, it will turn out that taking an Uber pool on a driverless electric van is the most cost-efficient and carbon-efficient transportation option for most short trips. However, where there is higher demand for corridor service, larger form factors are still optimal.
What are your wheels? What is your favorite bus route? Share your hot takes and cold servings in the comments.