Material sciences is a difficult field. People spend years researching one small area just to shelve their research as not viable, too cost prohibitive, or impractical for large scale manufacturing.

I haven't seen any research into durable biodegradable materials that could hold the weight of vehicles unfortunately, so I think investment will be hard to come by. Though I don't disagree with the premise that something that can degrade over time, but also not harm the environment would be an ideal solution to the problem. I imagine if such a thing were created it would be able to be applied to many other industries, not just transportation.