If riots break out, if you are caught in a city, you are done.
There will be a mad rush to exit the cities, and highways will be clogged. This makes it easier for the perpetually aggrieved to “Reginald Denny” people en masse.
The emergency services will fold, quickly, especially after the first fire fighter is shot. The fire services will not respond and there won’t be enough cops to escort them AND keep merchants from being looted.
Enough cops get killed, and they too will walk off. Just like in Katrina, but nationwide. Every home that can be kicked in by the gangsta’s will be kicked in, and woe be to you if you ain’t down for da struggle.
Here is something else to consider. Many cities also have National Guard armories in them. The most organized and clear thinking will seize those, and even the most REMF outfit has automatic weapons.
There WILL be those who can organize those warring gangstas into a fighting force once they have a common enemy.
They also WILL come into the suburbs once the food in the city has run out. It will start as scouting forays and then mass movement. How far they move is dependent on the organization and strength of any resistance.
A lot of your scenario depends on what happens the next few years. If Obama gets back and fans the flames and cuts off funding for law and order, then things could happen relatively soon. OTOH, if we get milktoast as president, we could have a situation where black frustration builds quickly but is effectively dealt with (I hope).