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公共汽车需求理论和影响需求的因素
2.1介绍
本章基于1990年代之前和之后的研究，回顾了公共汽车费用、收入、服务和交叉价格弹性的文献。主要研究成果体现在短期弹性和长期弹性的区别；由城市的规模和不同的旅行目的所引起的票价弹性区域的变化；以及在价格变化大小情况下票价弹性的区别。在公交需求领域，对车票以及其他价格变化的反应力度的研究工作一直备受关注。需要说明的是，我们在这里描述的文献综述在本质上与一些正在进行中的项目有部分的类似。这一章的结构如下：在2.2我们描述了对公交需求和弹性审查的理论基础，紧随其后的2.3节是对经验证据的概述。
2.2理论
在2.2.1节中文章简要概述了汽车需求理论和影响需求的主要因素。之后的2.2.2节描述了不同弹性的概念和影响这些估计值的因素。
Bus demand theory and the factors affecting demand
2.1 Introduction
This chapter reviews the literature on bus fare, income, service and cross price elasticities based on studies prior to and after 1990s. Major studies reviewed have concentrated on the difference between short- and long-term elasticities; variation of fare elasticities across areas, by city size and for different trip purposes; and, on the difference in fare elasticities for small and large price changes. Research work on the dynamics of response to fare and other price changes in the field of bus demand have been scrutinized. It has to be noted that the literature review exposed here have placed emphasis on studies which are partly analogous in nature to the project in hand. This chapter is organised as follows: a review of theories underlying bus demand and elasticities is conducted in Section 2.2 followed by an overview of the empirical evidence in Section 2.3.
2.2 Theory
A brief overview of bus demand theory and the main factors affecting demand are discussed in Section 2.2.1. After that, different notions of elasticity and the factors affecting their estimations are presented in Section 2.2.2.
2.2.1 Bus Demand Theory and Factors determining Bus Demand
Demand is defined as the quantity of good or service that consumers are willing to buy at a given price in a given time period. In our context, the service is bus and the price is fare. Demand for bus transport or public transport in general is said to be a derived demand i.e. it is rarely in demand for its own characteristics, hence derived from other function. For example, an individual leaving away from Port-Louis who desires to eat and shop at “Le Caudan Waterfront” would see bus transport as a means to get there to satisfy his desire. So the more people are attracted to shop and eat in Port-Louis, the higher the demand for transport facilities there.
Some factors determining the demand for bus services are outlined below:
Price: the lower the price, the more people are likely to demand the service offered.
Relative prices charged by different modes/operators: e.g. the lower the price of taxi fares, the more people will shift from bus to taxi travel.
Passenger income: as income rises, so the amount of travelling for both leisure and business trips will increase.
Quality of service: the more comfortable, safe, reliable and faster it is, the more people are encouraged to use bus travel.
Elasticity Concept and Factors affecting Transit Elasticities
Fare is a backbone in the functioning of public transport as it generates revenue to operators. The effects of fare changes on bus patronage, ridership or simply bus demand, can be measured in terms of elasticities. Economists define elasticities as a measurement of price sensitivity of the percentage change in consumption of a good caused by a 1 % change in its price or other characteristics.
Unit elasticity refers to elasticity with an absolute value of 1.0: price changes cause proportional consumption change. Elasticity values less than 1.0 in absolute value are called inelastic: prices cause less than proportional change in consumption. They are elastic if they are greater than one in absolute value: prices cause more than proportional changes in consumption.
In our context, the value of the fares elasticity is the ratio of the proportional change in patronage to the proportional change in fares. Generally, a bus fare increase brings to a fall in bus patronage i.e. they are inversely related. A zero to -1 value implies that a fare increase will lead to increased revenue. A more than -1 value suggests that a fare increase will be characterized by a decline in revenue.
There exist several methods for the calculation of elasticities (Pratt, 2003. The shrinkage ratio or factor, which is not an elasticity measure, explains the change in demand relative to original demand divided by the change in price relative to the original price.
The effect of the costs of alternative modes on bus patronage can be interpreted by making use of cross-price elasticities. These assess the percentage change in quantity demanded for, say bus travel, in response to a percentage change in the price of another service, such as motoring costs. For substitutable goods and services, the cross-price elasticity is positive while for complementary ones, it is negative. If the two goods/services are independents, it would be zero.
The income elasticity, which measures the percentage change in quantity demanded with respect to a 1 % change in income, ceteris paribus, is one way to analyse the effect of income on public transport demand. A less than one income elasticity is attributed to a necessity/normal good. A greater than one income elasticity reflects the characteristic of a luxury/superior good while a negative elasticity is associated with inferior goods implying that a rise in income brings to a fall in the consumption of a good. A zero income elasticity occurs when an increase in demand has no effect on the demand for a good.
Service elasticity indicates how transit ridership is affected by transit service quality factors such as availability, convenience, speed and comfort based on transit vehicle mileage, hours and frequency (Kittleson & Associates, 1999; Phillips, Karachephone and Landis, 2001). It is defined as the percentage change in transit ridership resulting from each 1% change in transit service. A negative sign indicates that the effect operates in the opposite direction from the cause (an increase in price causes a reduction in travel).
Taylor and Fink (2003) classified the factors influencing transit elasticity analysis into external and internal. External factors such as gasoline prices, cannot be controlled by transit systems while internal ones like fare levels are controllable. These are summarized below:
User type
Transit dependent travellers and discretionary or “choice” travellers (people who may use an alternative mode for that trip) response differently to a fare change. Because of this difference, we say that there is a kink in the demand curve (Clements, 1977), as illustrated in Figure 1. Generally, basic transit that serves transit dependent users is the less elastic portion of the demand curve, while service that attracts discretionary transit users is the more elastic portion of the curve. Non-drivers and college students are examples of dependent transit riders while drivers are considered as independent transit users.
Figure 1: A Kink in the Demand Curve
Price
Ridership
Source: Todd Litman (2007)
Time period
Fare elasticities are dynamic in nature i.e. they vary considerably with time as a result of fare changes. It is important to distinguish between short-run (SR), medium-run (MR) and long-run (LR). Explanations on SR, MR and LR elasticities can vary among authors. Most authors define SR to be 1 or 2 years; MR to be around 5 to 7 years while LR to be 12 to 15 years, or even more.
Geography
Residents of large cities are much more dependent on public transport than those in smaller cities for the simply reason that the more populated a city is, the greater the demand for bus services.
On the other hand, people in rural areas with low population density are likely to rely more on cars and less on public transport than urban residents as they have the option to switch to car if fare rises. So, fare elasticities may differ by area type.
Trip purpose
Peak journeys usually involve work and education journeys and are likely to be fixed in time and space while off-peak journeys which include leisure, shopping and personal business trips, are more flexible in terms of destination and time. So, off-peak elasticities will differ to peak ones.
Type of price change |
