There’s bad news for travelers and the climate in the latest policy brief from DePaul University’s Chaddick Institute for Metropolitan Development.

First the bad news: the pandemic discount on airline and Amtrak tickets has evaporated. Now more bad news: people are avoiding the smoky skies by choking the highways with private cars.

“Air and rail fares purchased three days in advance have risen sharply since late January, increasing by more $40 on one-way trips,” according to the report, titled Spring Surprise. “These changes are pushing more travelers onto the highways, primarily in private cars, but also onto intercity buses.”

If there’s good news in the report, for both travelers and the climate, it’s that those intercity bus fares continue to fall in price, which gives climate-conscious travelers a cheap and somewhat cleaner alternative to the private auto.

“Intercity bus fares, conversely, have mostly held steady and now average less than half that of train fares and only about a fifth that of airfares,” write the authors, Chaddick Director Joseph Schwieterman and Program Manager Crystal Bell.

Domestic airline flights emit the most greenhouse gas emissions per passenger by far, according to the UK Department for Business Energy and Industrial Strategy. The private automobile comes in second. Intercity buses emit less than half as much pollution as passenger aircraft and just over half as much as private autos.

The top climate performer is the train, which emits only about 16 percent as much as an airliner over the same distance. International rail in Europe emits just over 2 percent.

The Chaddick Institute authors simulated the behavior of travelers by searching on multiple booking platforms to find the best option on 19 popular routes in the United States. They found that the airlines and Amtrak are rapidly moving away from pandemic-related discounts for travel distances between 150 and 500 miles.

Fares across modes have increased in price since the pandemic eased, with the exception of bus fares purchased well in advance, according to the report:

“Bus tickets largely held steady, inching upward from $37 to $39 each way. However, most tickets bought farther in advance fell sharply.”

Car rental proved to be the most difficult and expensive option analyzed in the study:

“Median car rental prices (excluding fuel, insurance, and tolls) tend to be higher than airfares—if cars were even available, which was not the case on more than a third of the routes evaluated in late May.”