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HELICOPTER AIR SERVICE PROGRAM 455

From these scattered studies it is estimated that about 14 per cent of all commuters from metropolitan area suburbs to the central business district travel distances from 15 to 18 miles or over and that the average distance of all suburb-to-central business district commuters is between 10 to 12 miles. It must be stressed, however, that these are extremely rough approximations.

Considering length-of-trip characteristics alone, one may conclude that there is a significant potential for applications of vertical-life aircraft in commutation travel as a substantial number of people commute to work over distances where helicopter operations are feasible. In evaluating the VTOL market potential, however, it is necessary to consider, among others, the problem of consolidating traffic at suburban terminals in sufficient volume to support a frequency of scheduled service and the critical factor of lower-cost transportation provided by surface transportation, including readily-available private automobile.

Although trip lengths have been found to increase as the diameter of an urbanized area increases it is doubtful that the magnitude of this increase will significantly alter today's average—especially in the case of commutation trips as indicated by the following quotation:

[[block quote]] "The journey to work does not necessarily increase in length as the metropolitan area expands. As cities evolve, there is a pressure to minimize travel distances by reorientation of land uses as suburban areas tend to become self-sufficient." 1

The average suburban-to-downtown commuter will probably travel no more than 14 miles each way in 1975. This represents about a 15 per cent increase over 1960 estimates. The reason for this increase can be traced largely to expected improvements in transportation facilities, especially highway. For it has been noted that work trips in terms of time spent commuting tend to remain relatively constant. That is, a person is willing to spend only a certain amount of time traveling to and from work. If transportation facilities improve in terms of their speed characteristics then an individual can live farther out from his work without spending additional time commuting. Another force that will pick up average commutation distances is the expectation that higher-income commuters (generally living in outlying suburbs) will account for a larger per cent of the suburb-to-downtown commutation group. It is predicted that there will be approximately 1.1 million persons in the United States who will be commuting 18 miles or more in 1975. This is equivalent to 16 per cent of suburban commuters versus 14 per cent in 1960.

Mode of Travel

The private automobile is the dominant mode for journey-to-work travel in US metropolitan areas. 66.7 per cent of all commuters in the standard metropolitan statistical area (SMSA) used private automobiles or carpools and 18.7 per cent used public transportation (Table IV-2). Outside the central city, in the suburbs or fringe areas, 76.6 per cent used private automobiles and only 8.7 per cent used public transportation. In cities of over one million, however, the per cent using public transportation was 11.7 per cent; the per cent using automobiles was still high, 75.5 per cent. Even within the central city, supposedly the stronghold of public transportation, only 27.8 per cent used that form of commutation. In cities of over one million the percentage was 38.8 per cent, however.

The reasons for use of the private automobile in commutation travel are many. The basic factors—increased car ownership and residential land-use patterns—are interwoven with each supporting and, at the same time, dependent upon the other. The "move to the suburbs" which has been going on for decades has been made possible by the availability of the private automobile. In turn, the suburban area has been made increasingly dependent upon the automobile as the suburbs have grown away from existing rail and bus transportation systems. Land-use patterns have produced population densities so low that a substantial portion of the suburban area cannot not support bus transportation, despite its flexibility.

[[footnote]] 1 Future Highways and Urban Growth, Smith and Associates, New Haven, Connecticut, February 1961