You can also have friends block off sections of public roads either with their cars, yellow tape, etc. and then race. Have some sort of radio communication so all entrances and exits have guys as lookouts.
Just remember with public roads there is no "racing line" in mind....they are designed to handle a certain amount of speed and traffic...therefore you will be taking unconventional lines and with no practice, your braking zones are going to be all based on feel (additional note on bottom). Also, a word about passing. Most public roads have little or no passing corners, especially if the cars are set up equally. Be prepared for some very hairy turns, especially if you are going 2-3 wide in the straight.
Oh and a little note on how cops are able to catch most street racers is based on the fact that:
1. they have radios
2. they know the area, streets, braking zones, road conditions, directions, etc.
3. some are fairly decent drivers
Therefore, always plan an escape route. Map it out, pre-run it in the day time. Mark out your braking zones, practice (you don't have to go all out). Make sure you know what direction you are going and any surrounding surface streets. You notice that more emphasis is based on your escape than the actual race. This is assuming you are racing friends for fun...not a competition (for money) venture...and any run in with the LE would be highly detrimental.