It was outlawed in 1955 following the crash in that year’s Le Mans 24 Hours that killed over 80 spectators along with Mercedes driver Pierre Levegh.
Time trials have been the only legal form of motor sport since 1955. Five world championship Swiss Grands Prix were held at the Bremgarten circuit from 1950-4, and many Grands Prix were also held in the pre-championship years.
There was one Swiss Grand Prix during the ban, but that was held in France at the Dijon circuit at a time when French involvement in Grand Prix racing was particularly high.
But there remain great obstacles to a Swiss Grand Prix being held in Switzerland. The environmental lobby is strong in the country (the lifting of the ban passed by 97 votes to 77) and finding the support to build a new track would be difficult.