As fall term comes to a close, many Penn students begin locking down travel plans. Some will return home, some will travel elsewhere, and others will remain on campus or in Philadelphia. But out of the many students flying, driving, or taking a train elsewhere, it's important to consider the sustainability of travel choices.

It's natural to prioritize cost and convenience before taking into consideration the carbon emissions of their travel. This makes sense: certain forms of transit are prohibitively expensive, especially if you're taking them every break. And for some trips, only one travel option makes sense—taking a train or a bus to San Francisco can be impractical. However, for the portion of Penn’s student body that hails from the Northeast, what route should you take if you're keeping sustainability in mind?  

Addressing travel emissions is a little more complicated than you might initially think. While carbon dioxide (CO2) emissions per gallon of aviation fuel are comparable to those of standard gasoline—charting at 21.10 pounds of CO2 per gallon and 19.60 pounds, respectively—this ignores the fact that airplanes waste most of their fuel on the runway and during takeoff, rendering these numbers misleading. Furthermore, air travel creates additional pollution that includes water vapor, black carbon, nitrous oxide, and sulphur oxide. These, in turn, contribute even more to the greenhouse effect

All of these factors combined make the environmental effect of air travel worse than that of driving, even with the increasing levels of efficiency in airplane engines and fuels. And with the cheap pricing of jet fuels internationally, air travel is expected to take up more and more of the transit market share.

But we also need to consider the purpose behind some of these flights. Excessive tourism can lead to soil erosion, increased pollution, natural habitat loss, strain on water resources, and increased pressure on endangered species. While ecotourism is a growing movement, the vast majority of leisure travel still operates under standard consumption practices that add up to around 8% of global carbon emissions every year. It's important to consider the impact these trips can have on the environment. 

Trains ultimately end up being more sustainable than both driving and air travel. Coach buses, too, rank highly when it comes to reducing emissions. While there is little in the way of fully carbon–neutral transit options—very few people can ride a zero–emissions yacht like Greta Thunberg, due to cost barriers—trains and buses provide the lowest emissions footprint compared to the other modes of transportation that are currently available.

So if heading back home to somewhere in New England or the Mid–Atlantic, try booking a Megabus this year. When planning on travelling elsewhere, consider looking into eco–tourism options, or maybe rethink the need for a vacation at all. The best way to lower the environmental impacts of air travel is, unsurprisingly, not flying in the first place.