Rebuilding San Francisco´s transit system

SAN FRANCISCO is situated on the northern extremity of a peninsula, surrounded on three sides by water. Its population of 800,000 is confined within a rectangular area of 43 square miles. It is one of the hilliest cities in the United States, with land elevations varying between sea level and 930 feet. North of Market Street and the diagonal line bisecting the city, the streets are laid out in a substantially north-south, east-west grid pattern; see Fig. 1. South of this line the street pattern is made up either of smaller grids, oriented in many different directions, or of contour streets in and around the hillier sections.