The Shape of the 1980S: Demographic, Economic, and Travel Characteristics
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Transportation Research Record 807 27 reductions in use through price alone. In the REFERENCES aggregate, these effects are likely to cancel out and result in growth in VMT of 40-50 percent higher 1. Highway Travel Forecasts. FHWA, Nov. 1974. than during the 1975-1995 period. 2. N.S. Erlbaum, D.T. Hartgen, G.S. Cohen. NYS Other important demographic and economic factors Gasoline Use: Impact of Supply Restrictions and could significantly change these projections. Embargoes, New York State Department of Trans Trends toward greater automobile ownership per portation, Albany, Prelim. Res. Rept. 142, Aug. household but declining household size could add as 1978. mu,ch as 23 percent to travel projections over the 3. D.T. Hartgen and N.S. Erlbaum. Long-Range same period i decreasing urbanization could add Forecasts of Transportation Energy Consumption another 9 percent. But double-digit inflation, in New York State (Rev. Ed.). New York State higher unemployment rates, and periodic energy Department of Transportation, Albany, Prelim. supply shortages could more than cancel out these Res. Rept. 158, April 1980. effects. The net direction of all of these factors 4. Annual Automotive Fuel Economy Progress Report is difficult to determine, but on the whole, our to Congress. U.S. Department of Transportation, assessment is that, in spite of higher prices, the April 1980. likelihood of a stagnant economy, and possible 5. Charles Rivers Associates, Inc. Methods for supply shortages, travel is likely to grow, albeit Analyzing Fuel Supply Limitations on Passenger at a slower rate than in the 1960s and 1970s. Travel. NCHRP, Rept. 229, 1980, 132 pp. Gasoline use (already down since 1979) is likely to 6. D.T. Hartgen, A.J. Neveu, J.M. Brunso, continue to fall slowly. J.S. Banas, and J. Miller. Changes in Travel in U.S. energy policy, which so far has focused on Response to the 1979 Energy Crisis. New York new car efficiency and price decontrol, is generally State Department of Transportation, Albany, correctly placed. Specific actions to reduce trans Prelim. Res. Rept. 170, Dec. 1979. portation demand (and hence energy use) through 7. D.T. Hartgen and A.J. Neveu. The 1979 Energy modal diversion or decreased travel have been his Crisis: Who Conserved How Much? l.!l Considera torically cost-ineffective and will probably remain tions in Transportation Energy Contingency so. Such actions may be justifiable for other Planning, TRB, Special Rept. 191, 1980, pp. reasons, however. 157-165. In general, more attention needs to be placed on 8. C.E. Meyers. NYS Transportation Energy Data. such factors than nas been the case previously. New York State Department of Transportation, Projections of travel made in the 1970s are not Albany, Rept. No. 4, Nov. 1980. likely to include most, if any, of these concerns, 9. G.S. Cohen and M.A. Kocis. Components of Change particularly car efficiency, price rises, and infla in Urban Travel. TRB, Transportation Research tion. Some of this work can be done with existing Record 775, 1980, pp. 42-47. tools, but most of it cannot. New methods are 10. K.-W.P. Koeppel. Trends in Automobile Ownership needed that are sensitive to the joint interaction Patterns, 1973-1977. TRB, Transportation Re of these variables. Such methods need not be com search Record 723, 1979, pp. 1-6. plicated: In fact, simplicity and ease of use are 11. G. Shunk and C. Loxley. An Analysis of the highly desirable attributes. We hope that this Automobile: Modeling the Long Run Determinants ~aper contributes to that effort. of the Demand for Automobiles. Wharton Economic Forecasting Associates, Inc., Philadelphia, Feb. ACKNOWLEDGMENT 1977. 12. D.P. Sharp. Projections of Automobile Ownership I wish to express thanks and appreciation to those and Use Based on Household Life-Style Factors. members of the New York State Department of Trans Univ. of Pittsburgh, Ph.D. Dissertation, 1978. portation who provided input to this document. By its nature this document is preliminary. Errors of interpretation, fact, or omissions remain with me. I also wish to recognize the assistance of Karen Publication of this paper sponsored by Committee on Passenger Travel Demand Rapp and Diana Davis in preparing this manuscript. Forecasting. The Shape of the 1980s: Demographic, Economic, and Travel Characteristics FRANK SPIELBERG, EDWARD WEINER, AND ULRICH ERNST Forecasts of economic and demographic conditions are the base for all forecasts determinants of travel demand. For the past 25 of travel demand. During the 1970s many changes were observed in the demo· years, metropolitan planning organizations through graphics of the nation. This paper reviews the trends in pertinent demographic out the world have conducted surveys of travel, per measures and projects the directions of these measures through the 1980s. The formed analyses, and estimated models of travel objective is to determine how transportation demand is likely to change. demand, distribution, and mode choice. The projec tions of future conditions forecast by these models Transportation analysis is based on the premise that have been used to guide decisions on investments in demographic, social, and economic factors are major new and improved transportation facilities. 28 Transportation Research Record 807 Transportation planners have devoted extensive Figure 1. Family income distribution (in 1978 dollars). effort to ensuring that their models were statisti cally valid, replicated base-year conditions, and produced reasonable forecasts for future years. However, the validity of the forecasts of travel produced by any of these models can only be as good as the forecasts of the basic parameters on which the models depend {e.g., population and workers). Ul w Projections of these factors have most often not :::; been the responsibility of the transportation pro ~ fessional; rather, they are most often developed by ~ ..J other staff members and used with only cursory re <..J view as inputs for the transportation forecasts. ... 0 Fawcett and Downes (!) showed that the projec .... z tions of travel obtained by use of the carefully de w u veloped models are far more sensitive to changes in a: the values of the social and demographic parameters it than to misspecification of the model or slight variation in the model coefficients. During the past decade, significant changes have occurred in many of the social and demographic char acteristics of the U.S. population. As we enter the 1980s, it is useful to identify these national trends in factors related to transportation and to 1960 1965 1970 1975 1979 1985 1990 examine some conjectures as to their likely effect. APPROACH down [Figure 1 {_£)]. Since 1975, there has been an To obtain a picture of trends in 1980s, a wide range increase in the percentage shares of the two higher of existing forecasts and analyses was reviewed. income categories. Changes in the lower-income Evaluations were made of the most reasonable fore brackets were almost negligible. Trends over the casts based on the methodology used, consistency last two decades and current economic prospects sug with other information, historical trends, and fore gest that the income distribution will change little casts of other factors. during the 1980s. The percentage share of the high Travel information was developed by tabulating est income group is likely to increase slightly. data from the 1977 national personal transportation Smaller upward shifts should affect the other cate survey (NPTS). These data were stratified by house gories. But, overall, the experience of the 1970s hold size and location. Average weekday trip rates appears a better-suited model than the rapid gains by mode were calculated for each cell. of the 1960s. The income distribution forecast for the 1980s shows that close to 40 percent of u. S. Economy families will have incomes below $15 000. These families are apt to be severely affected by real in At the base of any projection of travel, explicit or creases in fuel costs. implicit assumptions are made about the economic conditions of the area under study. Projections of Total Population economic growth and its characteristics typically The total population of the United States will grow are no more than attempts to explore the implica at a modest rate during the 1980s. In the second tions of a particular set of assumptions about vari half of the 1970s, the average annual growth rate ous key factors. Changes in population, labor was 0. 73 percent--a full percentage point below the force, productivity, hours worked, tax policies, and rate for the late 1950s. Current census projections exports are the forces that determine changes in the for 1990 imply average annual growth rates between gross national product (GNP), personal income, and 0.6 and 1.3 percent, depending on assumptions about investments. fertility trends. Most experts expect that fertil The period from 1950 through 1973 {during which ity will rise slightly from its current low to the time the data used for most U.S. travel models were replacement level {the level at which the population collected) was a time of steadily increasing af would exactly replace itself in the absence of net fluence combined with steadily decreasing costs for immigration). At that level the U.S. population is automobile travel. Continuous increases in per projected to grow at a rate of 0.9 percent/year, capita travel were observed in almost all groups in from 220.5 million in 1979 to 243.4 million in 1990. the U.S. population. The direction of economic trends has been less clear in the last half of the Population Change decade. The rate of increase in the GNP has been reduced, and for individual households, the primary Of the three components of change in the total popu issue has been how to increase or maintain real in lation {live births, deaths, and net immigration in come in the face of significant inflation.