The highway is the backbone of the country's land connection, and the only real alternative you have if you are going from north to south (and vice-versa).
Until now, this might seem perfectly normal to you, until you grasp the fact that Chile also has one of the world's highest rate of fatal automobile accidents.
Therefore, your main objective when driving on the highway is to simply... survive.
Below are a couple of guidelines on how to do this:
a) Watch out for roadkill. Apparently, the native dogs consider the highway to be their graveyard, although the same can be said for cats, mice, humans, birds...
b) Watch out for potholes... sometimes it is just best to drive into the more shallow ones to avoid the big craters.
c) Disregard all "Men at Work" indications...
d) Officially, the speed limit is 100 km/h, but only if there are policemen in the area
e) Treat all vehicles as if they are wild animals... the average Chilean driver is unpredictable and seldom knows how to indicate properly
f) Avoid truck convoys at any cost
g) Personally, I haven't driven in the Atamaca desert, but bear in mind that extreme heat causes the Chilean drivers to make the dumbest manouevres.
h) Despite whatever claims you hear that most of the highway has two lanes in either direction, in reality it doesn't, so be very patient when it comes to overtaking.