Transportation enters into practically every phase of city planning, and a thorough study of the present and prospective daily movements of people, motor vehicles, and goods must be undertaken before the other phases may be worked out in detail. The principal object of the street system, for example, is to provide for free movement of people and goods; parks and recreation facilities should be easily reached by those who use them. The zoning plan and the street plan are interdependent, for the traffic on streets varies materially with the use of land fronting on them. Certain parts of the city should be easily accessible to other parts, and to transportation terminals. The location of street railways, bus lines, railways, waterways, and their terminals is itself one of the most important planning problems.