The route we followed is part of a popular tour circuit for backpackers and other tourist. It typically originates in either Uyuni or San Pedro and takes in the great Salar de Uyuni, Laguna Colorado, Laguna Verde, and other sites like Arbol de Piedre, Desierto de Dali and the Eduardo Avaroa Andean Fauna National Reserve.
From what we could see on the ground, and have read (or more accurately have not read) on the websites of other vehicle based travelers these trails are only traveled by the Toyota Landcruisers of the tour companies each packed with 5-6 guests and a driver (a bit squeezy), or the occasional mining vehicle. We have read no accounts from travelers in their own vehicle on this route. If you find such an account can you let me know.
Like much of our time in South America the decision to take this particular route was a last minute thing. We had spent about a month gradually making our way north from the Mendoza area through Northern Argentina towards the Bolivian border with the intent of crossing into Bolivia at La Quiaca/Villazon and thereafter heading to Uyuni via Tupiza. We had been traveling and gaining altitude slowly in order to be acclimatized by the time we arrived in Uyuni at 4000+m. After a few days in Tilcara checking up on those Landcruiser tours and some time to examine the tour route on Google Earth we decided we would try to drive our own vehicle from San Pedro to Uyuni.