Solo, also known as autocrossing, is an automotive competition in which cars are sent one at a time - hence the word "solo" - to negotiate a course composed of slaloms, Chicago boxes, hairpin turns and fast sweepers defined by traffic pylons. Finishing position is based upon elapsed time to complete the course, with the lowest time winning. Vehicle agility and handling are emphasized rather than brute power or top speed. The top speed encountered is normally less than legal highway speeds.
Practically anyone with any vehicle is allowed to enter a Solo event. There are separate classes for men and women plus a novice class for new-to-the-sport competitors. An entrant must have a valid drivers license and be at least 18 years of age (or have a SCCA minor release form signed by both parents or guardians). The vehicles must pass a safety inspection and be equipped with seat belts. Visitors are permitted free of charge to view the action, although no seating or other facilities are provided for watching.
The course is typically set up in a large parking lot using traffic cones to define the course. Any reasonably large paved surface may be used as long as it is relatively free of curbs, light poles, and major surface imperfections. Each competitor is allowed the same number of runs through the course in an attempt to achieve the lowest recorded time. The elapsed time will be adjusted for hitting a course pylon. The penalty is two seconds for each cone knocked down or out of it's marked box.
The competition classes are split into four general groups which allow increasing amounts of modifications. The four groups are Stock, Street Prepared, Prepared, and Modified. Each of these groups are further subdivided into classes based upon theoretical and/or actual performance.
In the Stock classification, which typically contains over half of the competing vehicles, very few modifications are allowed. Street Prepared vehicles are street legal cars with extensive bolt-on performance modifications. Prepared classes contain production cars which have been extensively modified and are used only for racing. The Modified classes contain purpose-built race cars, usually single seat specials.