Welcome to Subway 101, a new series in which we attempt to demystify the complex, enormous, and often-frustrating New York City subway system. First up: a guide to NYC Transit’s various subway cars.

Even the most oblivious straphangers knows that not all subway cars are built alike; the differences between the older and newer cars is quite obvious. But not everyone knows what, exactly, differentiates one dated car from another, or why so many types of subway car run throughout the transit system.

While the nitty-gritty details of subway car types may seem tedious, the quality of your commute often depends on it; the next time you’re stuck in a tunnel during yet another delay, the knowledge that you’re inside an R62 might improve the situation by a small amount.

The past

To understand where subway cars are now, it helps to understand their history. The earliest underground subway cars were wooden, previously used on the elevated lines. The change of material to steel was prompted by the 1918 Malbone Street Wreck, one of the deadliest train crashes in U.S. history, in which over 100 were fatally injured. Before it was controlled by a singular state agency, there were multiple private companies in charge—namely, the IRT, IND, and BMT—which ran many car models on the tracks over the course of the 20th century.

Some of the more memorable among them were the D-Type, or the Triplex trains, the short-lived Green Hornet, the blue and white BMT Bluebirds and Redbirds (one of which saw a second life as a rarely visited Queens tourist center before closing in 2015).

The New York Transit Museum, located in a disused subway station, is home to a fleet of vintage trains that the public can wander through. Every so often, these older models will run on the live tracks—during the holidays and for tours and baseball games—as the Nostalgia Train. The Frankenstein-d assortment of cars is usually composed of R1, R4, R6, R7A, and R9 models, all in the Arnine family—a fleet of similar cars manufactured for the IND lines in the 1930s to 1950 and used till the late ’70s.

There are also quite a lot of subway cars swimming with the fishes; many retired models are recycled by way of being sunk in the Atlantic, to form an artificial reef.

The current rolling stock

Excepting only a limited number of non-passenger cars, the modern R-model trains are used across the system today. The “R” number classification entered use in 1948, when the first batch was purchased for the IND. There are 15 different models running in the MTA’s current fleet of passenger trains, their numbers ranging from 32 (the oldest cars in the system, dating back to the 1960s) up to 188.

The observant straphanger will notice that the rolling stock that runs along the lettered lines (formerly the BMT/IND and officially known as the B Division), are significantly wider and longer, at 10 feet wide, than the numbered line trains. Those were once part of the IRT and are now known as the A Division; they’re roughly 8 feet wide.

Those paying attention will also realize that the car models can be grouped into three main aesthetic categories: There are newer cars with blue seating and brighter lighting; these began with the R142s, which run on the 2, 4 and 5 lines and were built starting in 1999. There are slightly older cars with multi-colored seats and jaundiced lighting, with their model numbers all under 100. And then there are the old R32s, with their corrugated exterior, most commonly found along the A, C, J and Z lines. (A fun fact about the R32s: Along with the second oldest models, the R42s, they’re singular in their dated seat layout.)

For train aficionados, there are a slew of ways to recognize not only the obviously different subway models, but also the minutiae that differentiates, say, a R142 and a R142A. The r/nycrail subreddit abounds with discussion of these nuances; many railfans can even recognize the differences between models based on the sounds they make when they roll into stations and open and close their doors. An entire YouTube subculture has been developed around it.

While a casual observer won’t get to the railfan level of knowledge overnight, here are some ways you can spot different subway car models, courtesy of a trivia r/nycrail mod:

The front LED sign of the R142 (2, 4, 5) is more recessed than the one on the R142As and the R188s (4, 7).

The car numbers of the R68 (B, D, N, W) are in the 2000s, while the R68A (A, B) have car numbers in the 5000s. They also use different fonts for the numbers (Akzidenz-Grotesk for the R68s, Helvetica for the R68As).

The front/rear cars (A cars) of the R188 (7) have CBTC equipment near the cab, taking up what was empty space on the R142/As.

R143s have tri-color LED displays inside, while R160s will either have an art poster or a full color LCD display in its place.

This one might be obvious, but the destination display of R142s turns off between text transitions, while the R142A doesn’t.

The exterior door lights on R160Bs have plastic caps that stick out of their metal enclosure, while the R160A doesn’t.

The R179 is slightly boxier than the R143 and R160s.

For further reading, the Wikipedia pages for subway rolling stock are known to be exceptionally thorough and accurate—thanks, in part, to two truly dedicated and knowledgeable teenaged Queens straphangers who have together edited hundreds of pages.

The future

While the subway’s decayed and aging signal system has deservedly been more in the spotlight lately, the MTA often appears more focused on modernizing its rolling stock.

Open-gangway cars are the way of the future: In late January, the MTA announced its formal approval of the R211 model cars, “535 state-of-the-art, next-generation” subway trains to replace older models on the lettered lines and the Staten Island Railway. Of these, only 20 will actually be open gangway, (the rest the familiar “closed-end” variety) and constitute a pilot program. These new poop trains will hit the tracks starting in 2020, but prototypes have been making highly anticipated debuts since December.