Take a look inside New York City's century-old subway system that more than 6 million riders use a day and that desperately needs an upgrade

New York City's subway system is one of the oldest metro systems in the world, and it's come a long way since its opening in 1904.

In the past 100+ years, ridership on New York City's subway system has grown to about six million daily riders, and commuters can now get on and off at 472 stations throughout the four boroughs of Manhattan, Brooklyn, Queens, and the Bronx.

But in one significant way, the Metropolitan Transportation Authority's (MTA) subway system has stood frozen in time, and it's causing major headaches for commuters.

The MTA reports that delays have more than doubled over the last five years, and, according to The New York Times, signal problems account for about 13% of all subway delays and are the second most common reason for weekday delays, after overcrowding.

Part of the problem is that the MTA subway system still operates using an antiquated signaling system called block signaling, which only allows MTA employees to see an imprecise location of where a train might be, and much of the technology that operates the trains is more than 100 years old.

While there is a plan in place to upgrade the signal system to a communications-based train control (CBTC) signaling system - a modern, computerized system that would reduce the space in between cars and allow trains to be stopped automatically - the upgrades can't come soon enough for many commuters.

And, unfortunately, due in large part to a lack of funding and the logistical nightmare it will cause to make these upgrades, at the rate things are going, New York City commuters may have to wait half a century to see the entire subway system upgraded, The New York Times reports.

Here's a look inside the outdated system that commuters will have to live with in the meantime:

Graham Rapier contributed to a previous version of this article.