In transport economic literature you can find two separate definitions of optimal subsidies for public transports. The first comes from a situation where a public transport operator maximises social welfare. As the consequence of both user and producer economics of scale, an optimal investment policy and optimal (marginal cost) pricing will lead to a financial deficit. A lump-sum subsidy to the public transport operator equal to this deficit will then be necessary to let the operator break even. Though the optimality has more to do with optimal investments and optimal pricing the resulting subsidy is sometimes also referred to as optimal. In what follows this lump-sum subsidy will be referred to as the break-even subsidy.

The other definition of optimal subsidies is the one that will be used here. This definition has more to do with the principal-agent theory and optimal incentives, and is valid in a situation where the transport authority, e.g. the local government hands over the provision of transport services to a private transport operator. The primary goal for the local government, (the principal), is to maximise social welfare, although the government may have some other goals as well, as safety or equity. The goal for the private transport operator, (the agent), however, is to maximise his own profit. The operator supplies transport services in a given area or for specific routes, either as the winner of a competitive tendering process or for some other, probably “historic” reasons. The operator is in a monopolistic position, and cannot be assumed to behave socially efficient. In this situation the government may use subsidies, in some way linked to the performance of the operator, to change the operator’s incentives and thereby affect his decisions. Of course the optimal subsidy is no longer a specific sum of money as in the first definition. Instead with optimal subsidies is meant a system of subsidization that will make the profit-maximising behaviour by the operator simultaneously fulfil the conditions for maximising social welfare.

Den mikroekonomiska analysen syftar till att förklara hur resurser fördelas i en ekonomi och hur priser och kvantiteter på en marknad påverkas av olika slag av störningar. Vidare behandlas frågor som hur effektiv marknaden är på att fördela resurser och vad som kan göras vid olika slag av marknadsmisslyckanden. De analysmetoder som används uppfattas dock av många studenter som svåra att tillgodogöra sig och framför allt brukar man efterlysa grundligt förklarade exempel som stöd för inlärningen.

Syftet med denna skrift är att om inte fullständigt täcka, så åtminstone delvis fylla detta behov. Här finns sammanställt totalt 121 uppgifter av varierande svårighetsgrad kring den mikroekonomiska modellen. Uppgifterna är uppdelade på fjorton olika områden och förhoppningsvis är lösningarna tillräckligt utförliga för sitt syfte. Även om uppgifterna spänner över vitt varierande områden gör de inte anspråk på att omfatta alla delar av den mikroekonomiska analysen. Områden som inte behandlas på inledande mikrokurser i Linköping utan tas upp först på kurser längre fram i utbildningen finns således inte representerade.

Uppskattningsvis hälften av uppgifterna är hämtade från gamla tentamina från 1985 och framåt, dock ofta omarbetade för att kunna täcka upp flera fall än vad man vågar behandla på en tentamen. Cirka 20% är äldre övningsuppgifter, medan 30% är helt nya uppgifter.

In the derivation of common travel demand models, it is customarily claimed that the main assumptions are based on microeconomic theory. However, the author investigates whether they are made mainly to justify existing models. The economic implications of the assumptions are not fully discussed. In some cases this results in models with characteristics that are questionable in the light of economic theory. In other cases theoretically possible but restrictive characteristics are given in advance rather than determined in the estimation process. The intercity travel demand model proposed in this study starts from the general assumption that travel demand can be derived from the more basic demand for visits to other cities. Then, necessary conditions for various demand elasticities are formulated and the consequences for the mathematical specification of the model discussed. Finally the model is estimated on Swedish data of intercity travel volumes for the period 1990-1994.

This dissertation deals with the estimation of intercity travel demand. The purpose is to discuss the derivations and characteristics of existing models, to derive a demand model based on microeconomic theory and to estimate the parameters of the model in order to gain information on important characteristics of the transport system.

The assumptions in the derivation of common travel demand models from microeconomic theory (gravity models, entropy maximising models and logit models) are often made only to support existing models and the economic implications of the assumptions are not fully discussed. In many cases this results in models with characteristics that are questionable in the light of economic theory. In other cases theoretically possible but restrictive characteristics are given in advance rather than determined in the estimation process.

The intercity travel demand model proposed in this study is based on the general assumption that travel demand can be derived from the demand for visits to other cities. As people living in different parts of a country experience different prices or "generalised transport costs" for visits to the cities, it is possible to estimate demand functions for visits to each city from the use of cross-sectional data, which is normally not possible for other utilities. From these demand functions, demand functions for separate transport relations can be derived. Necessary conditions concerning various demand elasticities are formulated and their consequences for the mathematical specification of the model are discussed. Of particular interest are those parts of the model that link together different levels. In order not to specify the cost function in advance, a Box-Cox formulation is used. The result is a demand model which determines the total number of trips made from each city, as well as the distribution among destinations and travel modes.

A simplified version of the model, not including distribution among travel modes, is estimated with Swedish data for the period 1990-1994. Estimations are made for the total number of trips as well as separately for business trips and private trips. The following results are the most interesting. There is strong support for the cost expression in the model to approach a power function, contrary to the exponential function that is given in advance in many other models. In the long run the demand for trips between two cities is elastic with respect to the generalised transport cost. Elasticities estimated range from minus one to minus two. About 80% of the additional trips caused by a decrease in costs are redistributed from other destinations, however, showing that in the long run the possibilities of substitution among destinations are good. Consequently, the relative effects of a general change in transport costs between all city pairs are smaller. Elasticities found in the study lie between -0,3 (private trips) and -0,5 (business trips).