The New York City subway is one of the most iconic subway systems throughout the world. With parts of it going all the way back to 1869, this subway system has been transformed numerous times throughout its life.
To be fair, in 1869 there wasn't actually a subway built, but rather a transit system under broadway that only spanned about 100 meters. It wasn't until 1910 that the BMT Broadway Line was built and the subway somewhat resembled what we think of today.
As decades pass, subway cars get old. They are fixed as much as possible, but eventually fixing them becomes more expensive than replacing them, at which point the cars are discarded. Initially these cars were sent to the scrapyard, where they were stripped and melted down, but interestingly enough this is a very expensive procedure that costs New York City millions each year. At about the year 2000, the MTA figured out a much cheaper way to dispose of the cars, dump them into the Atlantic Ocean.
At first, this sounds like a horrible idea. These trains are loaded with toxic materials that will surely kill all the sea life around the dump site. The reality is much different, however. Before being dumped into the ocean, each car is fully stripped of all potentially hazardous materials. They remove the windows, doors, seats, equipment, liquids and everything which is recyclable. Only the steel carcass remains. The cars are then disinfected and loaded onto a barge, where they sail off the coast and are dumped into the sea.
Since its inception, the MTA claims to have dumped over 2500 subway cars, as well as busses, signs, benches and much more. All items are thoroughly stripped and cleaned, then dumped. They claim that since 2000 they have saved over $12 million, and created a wonderful home for various undersea wildlife.
There have been numerous artificial reefs created from New Jersey to Georgia, all teaming with wildlife. Experts have been monitoring the progress of life in these reefs very closely and claim that many have seen a 4 fold increase in fish and wildlife around that region. Fish seem to love it, congregating around these reefs. Divers, too, have a great time monitoring this newfound home.
In all, this seems to be a huge success for the MTA and for the wildlife around. However, it has only been in action for about 15 years, not nearly enough time to make any definitive claims. Over time, things will become clear and in the worst case these artificial reefs will need to removed. However, judging by what we can see today, this isn't likely going to be the case.