I've only been studying Russian for about a year (and slowly at that), so I'm probably misunderstanding a lot.
From what I understand, though, идти and ехать are both unidirectional verbs of motion and basically mean "to go." However, идти implies walking and ехать implies some other form of transportation. I understand that it's more nuanced than that, because my professor has said that you can still use идти if you're driving a short distance in the context of your everyday life and it's not very important to specify that you drove.
I'm basically wondering about the history of this type of distinction (walking vs. other) and whether/how it has changed over time in the language. It seems like technology changes (more forms of transportation now than before, maybe less walking?) would have some sort of effect on the usage of идти/ехать and similar pairs like ходить/ездить.