Add alternative modes of transportation

[wrynearson]

Planes aren't the only way that people get around.

• [ ] 🚋 should be added in areas with good passenger rail coverage.
• [ ] 🚌 (long-distance) could be added.
• [ ] 🚗 (car-pooling) might make sense to add, but distances would be limited, and we don't want to promote driving if trains and bus options exist.

[nerik]

For trains in Europe, I can talk with Benjamin Tran Dinh and see if we can reuse some of his work.