OAKLAND, Calif. — The Bay Area Rapid Transit (BART) system has begun swapping out wooden railroad ties with plastic ones made out of recycled grocery bags, milk bottles and car tires. BART has replaced about 400 of its 38,000 wooden railroad ties with plastic ones so far, with plans to replace an additional 14,000 over the next decade.

The plastic ties are touted as stronger and more durable than wooden ties, lasting between 50-60 years as opposed to a wooden tie's lifespan of 15-40 years. BART is adding plastic ties, which can also be recycled at the end of their lives, as current ones wear out. Wooden ties that are taken out of the transit system, which covers the San Francisco Bay Area, are burned to make electricity through cogeneration.

The amount of plastic available to be recycled, though, could fall if researchers succeed in their work on biodegradable plastics. A Missouri University of Science and Technology team is working on creating plastics that can biodegrade in landfills within four months of disposal.

The research team is developing plastics for use in items such as bottles and drug delivery devices that would break down into substances that would be absorbed safely by living systems. They are focusing on bio-based, oil-based and natural polymers, especially renewable resources.

Along with making quickly-biodegrading plastics, the researchers aim to identify ways to make cheaper biodegradable plastics to spur widespread use and test the use of glycerol, a byproduct of making biodiesel, and polylatic acid, a renewable resource made from fermenting starch.