Drive to Tibet

Expect by air and train to Tibet, in fact you can drive there by yourself that you will found more interesting, but it may more different and harder than rail to Tibet or air.
Route 1:From Nepal.
Many travelers book overland tours via the Friendship Highway that runs from Lhasa to Kathmandu. The 920km (570 miles) trip is spectacular although don't expect a shower along the way. It takes three to five days with stops at sights along the way.
Route 2:From Golmud.
The terrain is desolate so it's not recommended unless you happen to find yourself in Golmud, wishing to be in Lhasa. If this is the case, you may have a better time on the train.
Route 3:From Chengdu.
For this route,private tour is allowable. You may find a travel agency or ask help for Tibet travel guide in Chengdu to arrange you a private tour with at least driver, guide & travel Tibet permit.