In the feature about the T’s badass antique trolleys this week, I quoted several railfans (definition: people who are obsessed with all things track-bound) discussing the irony of the longevity of the T’s oldest cars. Here’s the rub: the ancient PCCs on the Mattapan “high speed line,” which were built in 1945 and 1946, are still operating because they’re better and cheaper than anything else.

To think that the T would’ve been better off it hadn’t changed a thing since World War II sounds like misguided Luddite nostalgia, but it gets more convincing the more you learn about T history.

Historical epiphany number 1: The tunnels used to be cool

You know how Park Street Station is an airless tomb from June to August? Just like all the other underground T stations, which are also sweltering and breezeless in summer? Well, they’re not hot because of global warming or substandard building codes of generations past. The real reason the T is stuffy and hot is the fault of modern improvements, according to Gerry O’Regan, railfan and officer of the Boston Street Railway Association.

“Back before air conditioning was popular, the tunnels used to be nice and cool in the summer,” he says. “They used to be where you went to get cold in the summertime.”

Which makes sense, because they’re underground, a place where temperatures aren’t as extreme as they are on the surface. That’s why before refrigeration, people had root cellars. That’s why small animals in deserts (and people in Australia, while we’re at it) live in burrows and dugouts. Because of this, the T tunnels were designed with an average temperature of 50-60 degrees in mind, and kept breezy with a ventilation system of vents that let air from the tunnels into the cars.

So hot right nowSo what went wrong? Why are the once-cool tunnels now sweltering doldrums of death?

“It’s because the cars are air conditioned,” O’Regan says. “It heats the air discharged back into the tunnels, and works as a heat pump. It’s hot in summer because air conditioning is on. And the electronics in the cars and tunnels give off heat, too, which means that additional heat gets pumped back into subway. And there’s nowhere it can go.”

We’re hot because of the A/C? Holy ironic unintended consequences, Batman!

The only way to get the cool tunnels back, O’Regan says, isn’t to install more air conditioning, as people and the T seem to think. Instead, we should just trash the whole A/C system and go back to the root cellar model. “It’s called ventilation instead of air-conditioning,” he says.

Stay tuned: more lessons from antiquity to come.