From Milan: take the A4 motorway towards Torino, take the exit for A32 towards Bardonecchia.
From Turin: take the A32 motorway Torino -Bardonecchia take the exit for Bardonecchia or SS no 24 and 335 from Valle di Susa which ends at Bardonecchia.
From Lyon: take the A43 motorway towards the Frejus Tunnel, the first exit after you leave the tunnel is Bardonecchia.
Bardonecchia sits on the international train line Rome - Paris. There are direct trains from Turin (1h), Milan (2h), Paris (4h15).
You can find out the train times on Trenitalia's website: www.trenitalia.it