Actually I'd say the biggest things about riding on the street as opposed to anywhere else are that:
1. There's traffic coming at you in the other lane
2. That traffic is sometimes unpredictable and probably distracted
3. If you haven't been on that road before you have no idea about the sand/gravel/dead moose/tractor/oil spill/pothole the size of Mongolia/minivan full of children having a toilet break that may be round a corner that you can't see clearly.
1. There's traffic coming at you in the other lane
2. That traffic is sometimes unpredictable and probably distracted
3. If you haven't been on that road before you have no idea about the sand/gravel/dead moose/tractor/oil spill/pothole the size of Mongolia/minivan full of children having a toilet break that may be round a corner that you can't see clearly.