If you drive from St Moritz to Lugano via Italy, beware that the roads in Italy can be quite congested qwith a lot f traffic, especially along Lake Como. Many years ago I drove from St Moritz to Lugano via Italy. I aimed to arrive for lunch, and I ended up getting to Lugano after 4pm. There was a car towing a boat driving like 10-20km/hr, and no one could overtake that car.
Please also be aware that the Italian drivers are very aggressive. Another day I drove from St Moritz to Tirano, and returned via Livigno. A car overtook me in a very narrow tunnel (one lane, 2 way traffic) in high speed.