Here are some of the secrets of the New York subway that its workers like to keep to themselves.

The subways of New York run for more than 600 miles over and under the city. Each day of the week, more than five-and-a-half million people commute using the subway system from all over the five boroughs. Born of the merger of several subway systems, the Metropolitan Transit Authority has a few secrets that it keeps hidden from those commuters.

4. People got free rides in weird ways

Back when people used tokens to pay for travel, some discovered interesting ways to get around for free. In one, a person would stick a wrapper from gum or a scrap of paper in the token slot and then suck the token out after someone tried to use it. They’d also sometimes use Connecticut Turnpike’s cheaper tokens to get a cut-price ride.

3. A kid stole a train

Lots of youngsters love trains, but perhaps not to the extent that Keron Thomas did. When he was 16, he stole himself an A train. In 1993 he took off on a ride along the tracks for longer than three hours. He’d spent a lot of time studying manuals on how to drive it, and it has to be said, he did a decent job. No one ended up hurt in the incident.

2. A Nobel Prize-winner experimented underground

Austrian Victor Hess, who’d scooped the Nobel Prize in 1936 for discovering cosmic radiation came to America during World War II. And, naturally, he wanted to experiment with radiation. So he made Washington Heights’ 191st Street station, the system’s deepest, his laboratory. There he measured radiation levels in the granite between the station and Fort Tyron Park 180 feet above.

Image: Gary Hershorn/Corbis via Getty Images

1. Colored globes have meanings

It may look as though the colored globes are decorating the entrances that they top. But when they were put in during the 1980s, they represented a system based on traffic lights: green for stations with a booth for tokens open all day and night; yellow for stations with a part-time booth; red for stations that were exit only. Now they are a bit more straightforward: green for open, red for exit only.