All I remember about them from 10-15 years ago is that at that time they were rumored to be very difficult to sanction (by SCCA), and only a few were still grandfathered in at that time. I just checked the current rules online and the 2001 rulebook that I have here and neither mentions anything about a street solo.

They do include the following phrase, however:
"Except on permanent circuits such as kart tracks, the inner and outer limits of turns and corners should be marked by course markers; displacement of which results in time penalties. Corner limits must never be marked by curbs, buildings, poles, trees, soft shoulders or other hazards likely to cause damage to a car or likely to cause a car to overturn."

My old rule book talks about Solo I events and says something about top quality unpaved surfaces being okay for Solo I time trials, but the entire Solo I program has shifted to the Club Racing department and the new Solo rules have even done away with the "Solo I" and "Solo II" designations, with just the former "Solo II" being represented as "Solo".

Of course, Buddha's probably not looking to sanction under SCCA. Most independent clubs use K&K Insurance, and their guidelines are pretty loosely defined for autocross:
http://drivefast.org/wp/Misc/Safety_...quirements.pdf

I don't know if K&K has separate guidelines for rallycross or what they would think of a "street autocross". I know we once did a track event insured by them and they had some very strict guidelines differentiating a "driver's ed" event from a "racing" event, and the insurance for a race was much steeper. Insurance cost is based on the level of risk involved.

Might be worth a phone call to get with K&K and see what they have to say about what you should look for in a potential site for the kind of event you want to do.