Subway cars go through lots of maintenance before they reach a point where they would be retired. It isn't a decision that is reached casually since most subway systems remain "short" on operating stock. Even when they get the money to buy new cars there are usually lots of delays in production of new ones. \n
When they reach the point of loosing structural integrity it would be prohibitively costly to fix them. Stripped down, the shells are a good basis for building artificial reefs. Some construction/demolition material (concrete chunks with rebar) can also be used to build reefs. You can't just take take anything an dump it in the water (i.e., explosive demolition results in oil products and many toxic materials). \n
There are several big ticket pollution sources to worry about more than this. First is plastic--whether bags (which look like jellyfish to many predators like turtles) to the plastic connectors for 6 packs (which can entangle or constrict) these are everywhere in the ocean, though they tend to collect in certain areas due to ocean currents. Second is sewage, whether discharged by costal cities or by ships at sea (there are really weak controls over what a ship can dump at sea and what pretreatment of the waste has to be made--something to consider the next time you see a cruise line commercial). Third is industrial pollution, whether acid rain from smoke stacks or even just the fertilizer (mostly petroleum products) we use on lawns and farms, and the run of from the wastes created by feedlots (hog farms being one notorious source in the mid-Atlantic states).
The artificial reefs provide a habitat for fish and help moderate some of the shore erosion.
Of course if we could stop littering and dumping into rivers.....
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Subway cars go through lots of maintenance before they reach a point where they would be retired. It isn't a decision that is reached casually since most subway systems remain "short" on operating stock. Even when they get the money to buy new cars there are usually lots of delays in production of new ones. \n When they reach the point of loosing structural integrity it would be prohibitively costly to fix them. Stripped down, the shells are a good basis for building artificial reefs. Some construction/demolition material (concrete chunks with rebar) can also be used to build reefs. You can't just take take anything an dump it in the water (i.e., explosive demolition results in oil products and many toxic materials). \n There are several big ticket pollution sources to worry about more than this. First is plastic--whether bags (which look like jellyfish to many predators like turtles) to the plastic connectors for 6 packs (which can entangle or constrict) these are everywhere in the ocean, though they tend to collect in certain areas due to ocean currents. Second is sewage, whether discharged by costal cities or by ships at sea (there are really weak controls over what a ship can dump at sea and what pretreatment of the waste has to be made--something to consider the next time you see a cruise line commercial). Third is industrial pollution, whether acid rain from smoke stacks or even just the fertilizer (mostly petroleum products) we use on lawns and farms, and the run of from the wastes created by feedlots (hog farms being one notorious source in the mid-Atlantic states). The artificial reefs provide a habitat for fish and help moderate some of the shore erosion. Of course if we could stop littering and dumping into rivers.....