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Modal evolution of intercity travel demand: a Markovian analysis. Transpn res.
Z’ransgn Res.
Vol. 1, pp. i-viii.
Pergamon
TRANSPORTATION ENGLISH,
GERMAN,
Press 1967. Printed in Great Britain
RESEARCH
FRENCH
OF THE PAPERS
VOL. 1 No. 4
AND RUSSIAN
APPEARING
ABSTRACTS
IN THIS ISSUE
AARON J. GELLMAN: Implications for air carriers of the long-term transportation in the surface modes. Transpn Res. 1, 301-309.
prospects
for
cargo
For some years to come, the economic and service performance of cargo carriers operating in modes of transportation other than air will improve markedly. In general, such improvements will flow from intensive exploitation and evolutionary development of technology rather than through development of wholly new technologies. The most significant technological advances will relate to management and control technology. In addition, computer technology will be applied increasingly to enhance management’s knowledge of the economic and engineering nature of their operations. In turn, this will lead to significant pricing and service innovations. The net result of technological and managerial developments in the surface modes will be substantially improved transport service for the shipping (and traveling) public. Specifically, the real cost to the shipper of moving many categories of freight will be reduced and, perhaps more important, the level of service reliability in several of the surface modes will be greatly improved. In addition, as surface carrier managements become increasingly competitive across modal lines, they also will become more skilled in identifying competitive threats from new quarters and will take steps to minimize the harmful effects that such competition, if unchallenged, can have upon their own traffic volume and profits. ALAIN BIEBER : Modal Res. 1, 311-337.
evolution
of intercity
travel
demand:
a Markovian
analysis.
Transpn
Intercity travel demand is distributed between competing modes. In any market, the modal shares vary over time under the influence of technological changes in the status (cost, speed, frequency, comfort, etc.) of one or several modes. The class of historical models of modal evolution proposed in this paper considers the process of change as resulting from a system of intermodal migrations. Analytically, a sequence of vectors mt, whose components rnnt in an N-dimensional space define the level of activity of the N competing modes at time t, describes the market. Knowing the increment At between stages (t-l) and t in the global activity level of the market (all modes compounded), the evolution is simulated by a stationary Markovian multistage process (pO, P), obtaining an estimate fit of mt so that:
F?= Atp,+mt-lP
(1)
“Optimal” values of the parameters p,, (a row vector Nx 1) and P (a matrix of NX N transition probabilities) are obtained by minimizing over the time sequence a metric of the deviation vectors: d’ = m-r?. The metric used in this study is linear and calibration is made by linear programming. Knowledge of optimal parameters allows respectively the simulation and projection of past and future evolution through recursive use of expression (1). Several formulations of the problem are investigated by varying (i) criteria of goodness of fit between real and simulated modal volumes, and (ii) treatment of parameters pO. Particular attention is given to the asymptotic properties of these different formulations. The models are applied to the post-war evolution of the U.S. national market. Implications for the future of a simple perpetuation of past patterns of migration are discussed. Analytical uses of this approach are illustrated by completing, for each different formulation of the model, three calibrations: (i) on the complete calibration period; (ii) on the first half of this period, the “pre-jet” period; and (iii) on the second half of this period, the “post-jet” period. Corresponding simulations and projections provide, at the same time, a test of stationarity and an analytical appreciation of the impact of recent air technology on modal evolution.
Vol. 1, pp. i-viii.
Pergamon
TRANSPORTATION ENGLISH,
GERMAN,
Press 1967. Printed in Great Britain
RESEARCH
FRENCH
OF THE PAPERS
VOL. 1 No. 4
AND RUSSIAN
APPEARING
ABSTRACTS
IN THIS ISSUE
AARON J. GELLMAN: Implications for air carriers of the long-term transportation in the surface modes. Transpn Res. 1, 301-309.
prospects
for
cargo
For some years to come, the economic and service performance of cargo carriers operating in modes of transportation other than air will improve markedly. In general, such improvements will flow from intensive exploitation and evolutionary development of technology rather than through development of wholly new technologies. The most significant technological advances will relate to management and control technology. In addition, computer technology will be applied increasingly to enhance management’s knowledge of the economic and engineering nature of their operations. In turn, this will lead to significant pricing and service innovations. The net result of technological and managerial developments in the surface modes will be substantially improved transport service for the shipping (and traveling) public. Specifically, the real cost to the shipper of moving many categories of freight will be reduced and, perhaps more important, the level of service reliability in several of the surface modes will be greatly improved. In addition, as surface carrier managements become increasingly competitive across modal lines, they also will become more skilled in identifying competitive threats from new quarters and will take steps to minimize the harmful effects that such competition, if unchallenged, can have upon their own traffic volume and profits. ALAIN BIEBER : Modal Res. 1, 311-337.
evolution
of intercity
travel
demand:
a Markovian
analysis.
Transpn
Intercity travel demand is distributed between competing modes. In any market, the modal shares vary over time under the influence of technological changes in the status (cost, speed, frequency, comfort, etc.) of one or several modes. The class of historical models of modal evolution proposed in this paper considers the process of change as resulting from a system of intermodal migrations. Analytically, a sequence of vectors mt, whose components rnnt in an N-dimensional space define the level of activity of the N competing modes at time t, describes the market. Knowing the increment At between stages (t-l) and t in the global activity level of the market (all modes compounded), the evolution is simulated by a stationary Markovian multistage process (pO, P), obtaining an estimate fit of mt so that:
F?= Atp,+mt-lP
(1)
“Optimal” values of the parameters p,, (a row vector Nx 1) and P (a matrix of NX N transition probabilities) are obtained by minimizing over the time sequence a metric of the deviation vectors: d’ = m-r?. The metric used in this study is linear and calibration is made by linear programming. Knowledge of optimal parameters allows respectively the simulation and projection of past and future evolution through recursive use of expression (1). Several formulations of the problem are investigated by varying (i) criteria of goodness of fit between real and simulated modal volumes, and (ii) treatment of parameters pO. Particular attention is given to the asymptotic properties of these different formulations. The models are applied to the post-war evolution of the U.S. national market. Implications for the future of a simple perpetuation of past patterns of migration are discussed. Analytical uses of this approach are illustrated by completing, for each different formulation of the model, three calibrations: (i) on the complete calibration period; (ii) on the first half of this period, the “pre-jet” period; and (iii) on the second half of this period, the “post-jet” period. Corresponding simulations and projections provide, at the same time, a test of stationarity and an analytical appreciation of the impact of recent air technology on modal evolution.