It wasn't so long ago--the mid-1990s--that the northern Chilean desert had almost no coastal roads, and visiting port cities such as Iquique required an hour's detour or more from the Panamerican highway, which followed the interior rail routes established during the 19th-century nitrate boom. When I took the then unpaved road from Iquique south to Antofagasta in 1992, I met no other vehicles on a stunning Pacific shoreline route that's now the main paved highway connecting the north and south.
Things continue to change, though. A friend in La Serena has informed me that a new coastal road, from the port of Huasco north to Parque Nacional Llanos de Challe to Bahía Inglesa, is now open for traffic. I took the first part of this road, in the Norte Chico region about 700 km north of Santiago, a few years ago but could not continue beyond the village of Carrizal Bajo and had to backtrack east to the Panamericana in order to continue to Copiapó and Bahía Inglesa. Later this year I'll check out the new route.
Rarely visited, the vicinity of Llanos de Challe is one of the best places to see the "Desierto Florido," when sporadic spring rains cause ephemeral wildflower blooms that carpet the desert floor. This most often happens in September, but the rains are sporadic and geographically unpredictable. When it happens, though, Santiago travel agencies put together bus tours on short notice, and the new road is likely to make the flowering desert more accessible.