What is the main topic of this lecture?

Questions 17 to 20 are based on the following monologue about energy conservation. You now have 20 seconds to read Questions 17 to 20.
    For the past few weeks we’ve been discussing national energy conservation alternatives for the future. Today I’m going to talk about what one community is presently doing to conserve energy. The people of Davis, California have succeeded in cutting their energy consumption by one third since 1973. The first energy saving action that was taken in the early 70’s was the Legislation of Brick Building Codes. All new houses in Davis must have the proper heat insulation so that heat will not escape unnecessarily during the winter. New houses must also face north or south so that they will not be overheated by the sun in the summer. The law has had a definite effect. Since 1976 there has been a 50 percent savings in the amount of natural gas and electricity used in heating and air-conditioning.
    There were other energy saving features about Davis: buses partially supported by the city, transporting university students throughout the area. There are 24 miles of bicycles paths and today there are twice as many bicycles as cars in the city. By reducing the available parking space, the city council has succeeded in reducing the number of cars in the city every day. Another benefit of the reduced parking is the greater number of small cars. People are saving gas because they are preferring not to drive, or because they are driving fuel-economic cars. Davis, California has become an energy-saving model for other cities.
    Time is up for today. Next week we’ll return to our regular topic of national energy alternatives.