Actually that is a different bias you raise, Contrary Mary - the order of the options. People tend to pick the choices nearest the start of a list when they read the list themselves on paper or a computer screen.

Opinion Polls: Getting the results you want, from yes minister is sort of related.
youtube link

The core problem with the poll is that no-one knows if there is a practical solution to the parking/traffic problem for a one off event.

A traffic solution has not been offered by anyone, so why have it as a separate option?