Why Cities Need Trains: The Big Problem of Moving Millions

Imagine waking up one morning and looking out your window to see every single person in your city—all of them—trying to leave their homes at exactly the same time. Every single one. Moms and dads heading to work. Kids rushing to school. Grandparents visiting friends. Doctors going to hospitals. Pizza delivery drivers. Firefighters. Everyone, everywhere, all at once.

Now imagine trying to move all those people from where they live to where they need to be. It's like trying to pour an entire swimming pool of water through a garden hose. The hose wasn't built for that much water, and it's going to burst.

This is exactly what happens in big cities every single day.

A City the Size of Canada

Let's make this real with a number that might surprise you: Tokyo, the city we'll be exploring together in this book, has approximately 37 million people living in its metropolitan area. That's not a typo. Thirty-seven million.

To understand how enormous this number is, think about this: the entire country of Canada has about 38 million people. So imagine every single person in Canada—all of them, from the snowy mountains of British Columbia to the fishing villages of Newfoundland—all trying to get somewhere at the same time. That's Tokyo's transportation challenge, every single workday morning.

And it's not just Tokyo. New York City has about 20 million people in its metropolitan area. London has 14 million. São Paulo in Brazil has 22 million. Shanghai has 24 million. These cities, and dozens like them around the world, all face the same fundamental problem: how do you move millions of people from place to place quickly, safely, and reliably?

The answer, as you'll discover throughout this book, is something that has been around for almost 200 years: trains.

The Capacity Problem: Why Numbers Matter

Before we can understand why trains are so special, we need to understand a concept that transportation experts call "capacity." Capacity is simply the maximum number of people (or cars, or trains) that can pass through a certain point in a certain amount of time.

Think about a water pipe. A thin garden hose has a small capacity—it can only move a limited amount of water per minute. A big fire hose has a much larger capacity—it can move huge amounts of water very quickly. The same principle applies to transportation. A single bicycle lane has a small capacity. A busy highway has a larger capacity. A train system has the largest capacity of all.

Let's look at some real numbers that transportation engineers use every day. These numbers tell us how many passengers can move through a single lane of traffic in one hour:

| Mode of Transportation | Passengers per Hour per Lane | |----------------------|------------------------------| | Walking (wide sidewalk) | 8,000 | | Bicycle lane | 12,000 | | One car lane (with average 1.2 people per car) | 2,000 | | Bus lane | 8,000–10,000 | | Light rail (streetcar) | 10,000–15,000 | | Heavy rail (subway/train) | 80,000–120,000 |

These numbers are stunning when you really think about them. A single lane of subway track can move up to 120 times more people per hour than a single lane of car traffic. That's not a small improvement—it's a completely different order of magnitude.

Why Cars and Roads Can't Win the Numbers Game

Now, you might be thinking: "But cars can go anywhere! Roads go everywhere! Why can't we just build more roads?"

It's a great question, and transportation planners have spent decades trying to answer it with "more roads." Let's see what happens when cities try this approach.

In the 1960s, Houston, Texas, built the widest highway in the world at the time: the Katy Freeway. It had 23 lanes across (counting all the entrance and exit ramps). Transportation experts said it would solve Houston's traffic problems forever.

Today, the Katy Freeway is one of the most congested highways in the United States. The extra lanes didn't solve traffic—they encouraged more people to drive, and those people filled up the new lanes just as quickly as the old ones. This phenomenon is so well-documented that transportation scientists have a name for it: induced demand. When you build more roads, more people choose to drive, which fills up the new roads. The solution creates the problem it was trying to solve.

There's also a brutal mathematical reality that makes roads fundamentally unable to solve city transportation problems. Cars are big, and people need space.

A typical car is about 5 meters (16 feet) long. When cars are moving in traffic, they need to stay a safe distance apart—about 2-3 seconds of travel time worth of space. This means that in a single lane of highway moving at 60 km/h (about 37 mph), you can fit roughly 2,000 cars per hour. With an average of only 1.2 people per car, that's about 2,400 people per hour per lane.

Now let's think about space. One car in traffic, when you count all the space it needs (the car itself plus the gap in front and behind), takes up about 60 square meters of road. That's roughly the size of a small classroom.

But here's the thing: that car is probably carrying just one person. So for every person moving through that city, you need about 60 square meters of expensive, paved, maintained road. If you want to move 37 million people a day (Tokyo's challenge), and even if you assume that only half of them are traveling at once, that's 18.5 million people. At 60 square meters per person, you would need more than 1,100 square kilometers (425 square miles) of road space just for the cars. That's larger than the entire city of Tokyo itself—and that's not counting the roads people walk on, the buildings, the parks, or the places where people actually want to go.

The math simply doesn't work. Roads and cars cannot be scaled up to handle the population of a modern megacity.

Trains: The Mathematical Solution

So if roads can't solve this problem, what can? The answer is trains—and the key is understanding why they are so much more efficient.

The magic of trains comes down to three factors: they run on fixed tracks, they can be coupled together in long strings, and they move on paths that are separate from everything else.

Let's break each of these down.

Fixed tracks might not sound exciting, but they allow trains to be much more efficient than cars. When a train leaves a station, it doesn't have to worry about traffic, red lights, or pedestrians crossing the street. It follows its track like a river following its bed. This means trains can maintain consistent speeds without the constant stopping and starting that makes car travel so inefficient.

A subway train in Tokyo might stop at 10 stations on its route, but each stop only takes about 30 seconds (compared to a car waiting at a traffic light for 60-90 seconds, and then having to accelerate again). Over a journey of 10 kilometers (about 6 miles), those time savings add up dramatically.

Coupling cars together is the second secret. Imagine trying to move 1,000 people using cars. You'd need about 833 cars (assuming 1.2 people per car). That's a lot of cars, and you'd need 833 drivers, and they'd all need space on the road.

Now imagine a train doing the same job. A typical subway train in Tokyo carries about 1,000-1,500 passengers. One train. One driver (sometimes no driver at all—more on that later). And that train takes up about the same amount of space on the tracks as maybe 5-6 cars lined up together. Suddenly, moving 1,000 people requires a tiny fraction of the space that moving 1,000 people by car would require.

Here's another way to think about it: if you lined up all the cars needed to move the people on a single Tokyo train during rush hour, the traffic jam would stretch for about 15 kilometers (9 miles). The train moves that same 1,000 people in a space about the length of two football fields.

Separate pathways are the third advantage. Trains run on their own dedicated tracks that nothing else can use.