Minimum amount of Base Stations

Let's consider a long, quiet country road with houses scattered very sparsely along it.
(Picture the road as a long line segment with an eastern endpoint and a western endpoint.)
Further lets suppose that despite the country setting, the residents of all these houses are
avid cell phone users. You want to place cell phone base stations at certain points along
the road, so that every house is within four miles of one of the base stations. Give an
efficient algorithm that achieves this goal using as few base stations as possible.