While working on a somewhat related piece tonight, I started collecting a series of numbers regarding the last few decades’ worth of subway ridership that I wanted to share. These numbers tell a story of a city that’s growing and a transit agency that’s going to struggle to keep up. They tell the story of planners potentially caught off guard and economics and construction timelines that are impossible to sustain. The numbers leave many questions up in the air, and I’m not quite sure what the next few decades will bring.

Let’s start in September of 1996. Right before MetroCard discounts were announced, the average daily subway ridership was 3.684 million. Four years later, in September of 2000, daily subway ridership hit 4.745 million. Last October, average daily subway ridership reached 5.974 million. So in the span of 20 years, the MTA saw, on average, 2.3 million more entries per day or an increase of nearly 66 percent. That is, simply put, remarkable growth. On an annual basis, in 1992, overall ridership was below 1 billion; in 2015, that total topped 1.762 billion.

On the other hand, in the intervening twenty years, the MTA has opened a new station, and that new station has been open only since September. The agency is currently constructing three more with the first substantial addition to the subway map in a generation set to open within the next seven months (give or take a few), but this seems like a woefully inadequate response to a system that would have felt downright empty in the early 1990s as compared with our packed trains at most hours of the day.

This is, in a nutshell, the capacity crisis that has gained recent headlines. As I wrote last week, there are few immediate solutions and most transportation proposals seem to be bespoke ones driven by outside interests. The Brooklyn-Queens Streetcar, for instance, is going to do diddly-squat to help a Bronx commuter find a few square inches of space or a Q train rider at 7th Ave. fit into a Manhattan-bound subway at 8:30 a.m. Bike share solves some of the city’s last-mile problems, and despite my annoyance with the attention on ferries, they can help around the margins. But when a good year for the ferry system means 1.2 million riders over the course of 365 days (or 20 percent of today’s total subway ridership), we’re really comparing apples to oranges.

Today, we’re living with the consequences of both deferred maintenance and a lack of foresight. At some point in the 1930s, for a variety of historical and economic reasons, New York City simply stopped expanding its subway, and a few decades later, the city stopped investing in regular upkeep. Thus, when the state took over, it had a backlog of maintenance and no money for expansion. Today, the subway still needs money for maintenance, but the MTA can’t expand fast enough or cost-effectively enough to meet demand. (In 2007, when the Second Ave. Subway broke ground, annual ridership was 1.56 billion — over 200 million less than it is now.)

So what happens? I’ve been beating the drum for open gangways for a long time, and it’s a solution the MTA needs to explore and adopt as soon as possible. It’s also imperative to find a way to build faster and cheaper. Many options are simply fingers in the dike of a flood of riders, and without a commitment to a high-volume, cost-effective expansion effort, the subways are going to be this crowded for decades to come. And what happens if ridership growth continues on its upward trajectory? That may just be a question without an obvious answer.