Here is a quick share of an article regarding animal crossings and roads/highways:

I thought the article was interesting not just because it featured animal crossings but because the very same ideas and design interventions may be adopted for humans as well. Indeed, there will be cost implications but that is only because we have been accustomed to designs that favor car use more than the movement of people. Perhaps we should rethink how we design infrastructure such as our roadways for them to be favoring active transport and employing more nature or environment-friendly features.