I think you may have slightly mixed up Fasnacht (a doughnut eaten on Shrove Tuesday) and Fastnacht, Tim. The Swabian-Alemannic Fastnacht festival encompasses Shrove Tuesday, but is much more than just that. Added to which, Shrove Tuesday 1939 was on February 21st.
The two restaurants named both seem to still be in existence, although the addresses given for the start points don't - or at least Google maps doesn't recognise them! - but other research I've done re Swiss addresses suggests this isn't unusual. Having looked at the restaurant locations, which seem to be on pretty flat ground, I'm leaning more towards the pedal car/soapbox/billycart option rather than toboggans.
To put that into context, the American Soapbox Derby had been going since 1934. It had certainly been covered by the European motoring press and at almost exactly this time in Britain the Scout Association was launching its own version. Rather than the straight courses and 'gravity racers' used in America these were pedal-powered and had to be capable of being steered. All for a maximum budget of fifty shillings. From reports I've found, the most successful ones incorporated bicycle gears - one was even said to have independent suspension on all four wheels!