Washington, DC to Boston

Between Washington, DC and Boston, 4.1 million passengers flew nonstop in 2025, on 46 thousand flights of about 383 miles and 1.1 hours in the air. The average passenger accounted for about 100 kg of CO2 from the fuel burned, from 67 kg on Spirit Airlines to 165 kg on PSA Airlines.

Washington to Boston has a train, and the figures aren't close: about 10 kg per passenger on Amtrak's Northeast Corridor, against 100 kg for the average passenger on the flight. That's ten times as much, and the EPA's default for a flight this length (49 kg) is only half the figure measured from the airlines' filings.

It's also the one of the 15 busiest routes that has got noticeably worse, from 92 kg in 2019 to 100 kg, up 8%. Regional jets are behind it. Republic, PSA and CommuteAir, with 50 to 74 seats a flight, carried 8% of the passengers in 2019 and carry 23% now, at 136, 165 and 131 kg.

100 kgCO2 per passenger, average
383 milesabout 1.1 hours in the air
4.1 millionpassengers in 2025
77%of seats filled

CO2 per passenger, airline by airline

Kilograms of CO2 per passenger, one way, 2025. Fuel burned only. Less is better.

Washington, DC to Boston by airline, 2025

Airline	Share of passengers	Flights (thousands)	Main aircraft	Seats per flight	Seats filled	kg CO2 per passenger
Southwest Airlines	37%	12.9	Boeing 737-700, Boeing 737-800	161	74%	75
Republic Airways	16%	11.4	Embraer 175	74	76%	136
JetBlue	12%	5.4	Airbus A220-300	114	80%	118
American Airlines	11%	4.6	Airbus A319, Boeing 737-800	130	79%	106
United Airlines	11%	3.1	Boeing 737-900ER, Boeing 737-800	172	86%	73
PSA Airlines	6%	4.4		68	79%	165
Spirit Airlines	2%	0.7	Airbus A320-200, Airbus A321	195	71%	67
CommuteAir	2%	1.8		50	83%	131

What explains the differences

It's number 11 of the 100 busiest city pairs by passengers, and number 95 for the lowest CO2 per mile flown (0.26 kg per passenger-mile, number 1 being the lowest). A typical route of 383 miles in this set comes out at about 76 kg, so this one is 32% above it.

The flights use more than one pair of airports: BOS to DCA (34%), BOS to BWI (20%), BOS to IAD (11%). The figures here cover all of them.

The airlines on this route differ by 148% per passenger. Spirit Airlines burned 951 gallons per flight and 139 passengers on each, and PSA Airlines 911 gallons and 54 passengers. The gap comes from how many passengers share each flight, not from fuel burned per flight. Spirit Airlines flew 71% full here against 79% for PSA Airlines.

For comparison, the EPA default factor for a flight of this length (0.129 kg per passenger-mile) would give 49 kg. The EPA figure is a national average for flights of that length. The measured figure for this route is 102% higher.

2019 compared with 2025

In 2019 the route carried 4.7 million passengers on 50 thousand flights. In 2025 it carried 4.1 million, down 14%, on 46 thousand flights, down 9%. The average flight had 116 seats then and 115 now, and 81% of them were filled against 77%.

CO2 per passenger was 92 kg in 2019 and 100 kg in 2025, up 8.4%. Fuel burned per flight was up 2.4% (895 gallons to 917) and passengers per flight were down 5.6% (95 to 89). The distance flown was about the same (381 miles then, 383 now).

Southwest Airlines led in both years, with 39% of passengers in 2019 and 37% in 2025. Republic Airways gained the most share, 4% to 16%. JetBlue lost the most, 20% to 12%. CommuteAir didn't have 1% of the passengers in 2019 and now carries 2%. Mesa Airlines no longer reaches 1% of passengers, having had 2% in 2019.

Airline by airline, United Airlines went from 76 kg to 73 kg per passenger (163 seats per flight to 172, main aircraft Boeing 737-900ER in both years); PSA Airlines went from 123 kg to 165 kg per passenger (61 seats per flight to 68, main aircraft unlisted aircraft in both years).

Washington, DC to Boston, 2019 and 2025

Measure	2019	2025
Passengers (thousands)	4,749	4,101
Flights (thousands)	50.2	45.9
Seats filled	81%	77%
Gallons of fuel per flight	895	917
kg CO2 per passenger	92	100

Kilograms of CO2 per passenger on the airlines that flew the route in both years. 2019 figures use that year's filings and estimated aircraft fuel rates, with type-average replacements for missing or outlying filings as described in the methodology. Less is better.

Washington, DC to Boston and back: time in the air

Flights from Boston to Washington, DC spent 74 minutes in the air on average in 2025, against 62 minutes from Washington, DC to Boston: 12 minutes longer, 20% more. That's the westbound direction, into the prevailing west-to-east winds, which at flight levels often blow at well over 50 miles an hour.

At this route's average burn of about 806 gallons per flight hour, those extra minutes cost about 164 gallons per flight, which is about 1.8 gallons or 18 kg of CO2 for each passenger on the slower direction. The route figure above averages both directions.

Time in the air by direction, 2025

Direction	Average minutes in the air	Flights
Boston to Washington, DC	74.3	22,896
Washington, DC to Boston	62.1	22,981

Fly or drive

Driving is about 448 miles by road, which we estimate as 1.17 times the straight-line distance. An average car emits about 133 kg of CO2 on the trip, at the EPA figure of 0.297 kg per vehicle-mile. Alone, that's 33% more than the 100 kg for a passenger on the flight.

With 2 people in the car, driving comes out lower per person than the flight (67 kg each, and 33 kg each for four). A larger SUV or pickup (0.394 kg per mile) would emit about 177 kg per vehicle.

A direct Amtrak train serves both cities. Using the EPA figure for the Northeast Corridor (0.023 kg per passenger-mile, mostly electric) and a rail distance about equal to the road distance, a train passenger would account for roughly 10 kg, 90% less than the flight.

CO2 per person, Washington, DC to Boston. Driving figures divide one car's emissions between the people in it. See flying vs driving for other trip lengths.

Flights are listed under the airline that operates them, so regional flying appears under the regional. How the CO2 and drive figures are worked out is in the methodology.

What to take from it

The mainline jets are the cheap end. Southwest at 75 kg and United at 73 kg fly planes of 161 and 172 seats. 'Boston' and 'Washington' are both a group of airports: 28% of the passengers use Providence or Manchester, and Baltimore takes 40%.

The flight out of Boston is 12 minutes slower than the one back, 20% longer. Passengers are 14% below 2019. A car with three people on the 448 miles of road comes to 44 kg each, 56% below the flight, and the train beats both.

Routes with shared cities or nearby CO2 per mile

Airports on this route: Ronald Reagan Washington National Airport, Baltimore/Washington International Thurgood Marshall Airport, Washington Dulles International Airport.

Airport and airline references

Source: US Bureau of Transportation Statistics (BTS), T-100 traffic and Schedule T-2 fuel filings; US EPA transport emission factors. See the methodology.

See all routes, or how the airlines compare overall on the airline pages.