Go Metro, Go Green, Save the Planet: an Expo Line test train in the Northvale Trench in Cheviot Hills. Photo by Steve Hymon/Metro.

Sure, that headline is a self-serving message. But hey, I work in PR for a major transit agency.

Here’s the thing: it’s actually a message that a lot of people should be shouting on Earth Day and, quite frankly, every day.

Why? As I’ve written time and again on the Metro blog, studies have shown that generally speaking taking transit results in fewer greenhouse gas emissions than driving alone.

The reason for this is that buses and trains can carry a lot more people more efficiently than the average car in the U.S. If you really want to fight climate change, then get on a crowded bus or train — the more people on board, the more efficient it is.

I’ll go a step further: if you want to fight climate change, support spending on more transit in big cities.

Fun fact #1: more than one-third of the United States’ population lives in the 20 largest metro areas in the country.

Fun fact #2: many of those metro areas suffer from bad traffic. “Traffic Gridlock Sets New Records for Traveler Misery,” proclaimed the Texas Transportation Institute’s annual congestion report last year.

Fun fact #3: the transportation sector — i.e. driving — is responsible for 26 percent of the nation’s greenhouse gas emissions.

Given these realities, maybe it’s not a horrible idea to invest more dollars in transit serving big metro areas — where there exists the possibility of prying people out of cars that otherwise may be idling in traffic. Sure, cars are getting more fuel efficient, but so will transit — especially rail that runs on electricity — as more renewable power supplies come online.

While federal spending on transit has inched upward in recent times, the $3.5 billion allotment for new transit projects in 2016 is kind of small potatoes compared to the entire federal budget (see this cool but depressing chart). Unless the U.S. has a massive back to the farm movement, chances are we’re only going to become even more urbanized.

Which is another reason that building transit in cities makes sense.

Finally, a few words for my colleagues in the transit industry: let’s not be shy about marketing transit as part of the battle against climate change. We’ve beaten the old marketing tropes to death about traffic, the expense of car ownership and parking.

It’s time to do something different, and do something important. Like saving the planet.

Related: Here’s Metro’s most recent annual sustainability report, which covers the agency’s many efforts to use resources — including fuel and electricity — more efficiently.