Like the answer to Paint the Earth, the answer to the first part of this question is pretty straightforward to look up.
But what if it weren’t? Can we figure out the answer from things we already know? Let’s look at a few ways of estimating it.
First of all, how wide is a street? I’ve never seen one of those flashing crosswalk countdowns signs start with less than 10 seconds; if people walk at a meter per second, most roads are probably at least 10 meters wide.
via xkcd
