What is the test for forfeiture of a vehicle used in soliciting prostitution?

"We summarize: Vehicle Code section 21 precludes local regulation of `matters covered' by the Vehicle Code, absent express legislative authorization. The use of vehicles in soliciting prostitution is a matter that the Vehicle Code covers in section 22659.5, which establishes a five-year pilot program under which cities and counties may treat as a public nuisance any vehicle used in soliciting prostitution, but that pilot program does not allow for forfeiture of the vehicle. There being no express legislative authorization for any other form of local regulation of the matter covered by Vehicle Code section 22659.5, Vehicle Code section 21 precludes an ordinance like [Oakland's], which seeks to regulate vehicle use in soliciting prostitution by requiring forfeiture of the vehicle. Under Vehicle Code section 21, therefore, the City's ordinance is expressly preempted by state law." (O'Connell v. City of Stockton, supra, 41 Cal.4th at pp. 1073-1074, 63 Cal. Rptr.3d 67,162 P.3d 583.)