No, it's not a heat-induced hallucination: that really is a newer model C train rumbling down the tracks. But it's part of an annual summer subway switcheroo.

Here's how it works. Most months of the year, R32s ply the C line. Built in 1964, they're the oldest cars in the city's subway fleet. While those 222 cars are the workhorses of the MTA, summer temperatures tend to stress them out.

"What we want to do is really show the R32s some love by not running them entirely underground where their A/C units tend to take a beating," said MTA spokesman Kevin Ortiz, who pointed out the C line runs entirely underground. So the MTA takes some newer trains (the R160 model) from the J line, and moves the R32s to both the A line and the J line, which get to experience the outdoors.

So what normally plies the C line three seasons of the year:

(Fan Railer via Wikimedia commons)

is replaced by this:

(Adam Moreira via Wikimedia commons)

But don't get too used to it: when temperatures drop, the R32s will be pressed back into service on the C line. And you'll be seeing them for the foreseeable future: MTA says C trains won't get upgraded until 2017. As Gothamist put it in back in 2011, "we get to keep our vintage C train fleet for six more glorious years."