Via Salis is the name of the first PPP (Public Private Partnership) project in the Czech Republic. The newly built section of the D4 motorway will offer travel on a road that meets all the criteria of safety and comfort and modern technological parameters. While the motorway itself will run along a new route, the link between Příbram to Písek follows one of the oldest trade routes in the country. It is part of the so-called Salt Trail, also known as the Golden or Passau Trail.