تجزیه و تحلیل کشش تقاضای بنزین در سطوح ملی و محلی در مکزیک

The majority of evidence on gasoline demand elasticities is derived from models based on national data. Since the largest growth in population is now taking place in cities in the developing world it is important that we understand whether this national evidence is applicable to demand conditions at the local level. The aim of this paper is to estimate and compare gasoline per vehicle demand elasticities at the national and local levels in Mexico. National elasticities with respect to price, income, vehicle stock and metro fares are estimated using both a time series cointegration model and a panel GMM model for Mexican states. Estimates for Mexico City are derived by modifying national estimates according to mode shares as suggested by Graham and Glaister (2006), and by estimating a panel Within Groups model with data aggregated by borough. Although all models agree on the sign of the elasticities the magnitudes differ greatly. Elasticities change over time and differ between the national and local levels, with smaller price responses in Mexico City. In general, price elasticities are smaller than those reported in the gasoline demand surveys, a pattern previously found in developing countries. The fact that income and vehicle stock elasticities increase over time may suggest that vehicles are being used more intensively in recent years and that Mexico City residents are purchasing larger vehicles. Elasticities with respect to metro fares are negligible, which suggests little substitution between modes. Finally, the fact that fuel efficiency elasticities are smaller than vehicle stock elasticities suggests that vehicle stock size, rather than its composition, has a larger impact on gasoline consumption in Mexico City.

Although there is an extensive literature on the effect that prices, incomes, and other factors have on the demand for gasoline, most studies use national data that produce elasticity estimates at the country level. There is, however, no a priori evidence to presume that gasoline demand elasticities estimated with national data reflect conditions at the local level. 1 Half the world's population now lives in urban areas, and the largest growth in population is taking place in cities in the developing world ( UNFPA, 2007). Therefore, for rapidly growing cities to adopt sustainable policies to respond appropriately to urban and global environmental challenges from excessive use of the private car, it is of paramount interest to concentrate on the estimation of gasoline demand elasticities at the local level. Data from the International Energy Agency show that Mexico is the 5th largest gasoline consumer among OECD countries, with total gasoline consumption comparable to that of Germany and the UK. Per capita gasoline consumption in Mexico City is equivalent to that of developed countries such as New Zealand and Switzerland, taking 6th place among OECD countries. Therefore, due to increasing concerns of the contribution of road transport to climate change, and the rapid rate at which cities in the developing world are growing, the aim of this study is to estimate and compare gasoline demand elasticities at the national and local level in Mexico. In order to obtain reliable demand estimates for a specific transport sector, one cannot rely on average estimates for similar sectors or countries; a detailed study of that market must be performed, which is the aim of this paper. The study places special attention on the methodological issues and theoretical foundations of the latest econometric techniques developed in the recent literature. Elasticities with respect to price, income, vehicle stock, and metro fares are estimated for Mexico at the national level with a time series cointegration model for the period 1980–2006 and a panel GMM model with data from 30 Mexican states over the period 1993–2004. Even though monthly data on gasoline consumption for Mexico City are available since 1993, data on income at the Mexico City level are only collected annually and proxies for monthly income are either only available at the national level or for a very short time series. Therefore, due to lack of availability of a time series or panel data set for Mexico City, gasoline per vehicle demand elasticities for Mexico City are derived from national elasticities and mode shares at the national and local level, as suggested by Graham and Glaister (2006). We also estimate local elasticities with a panel Within Groups model with data aggregated at the Mexico City borough level where gasoline consumption per vehicle is derived from car kilometres and fuel efficiency per vehicle for the period 2001–2004. The remainder of this paper is structured as follows: Section 2 presents a brief literature review of elasticities of demand for gasoline and presents the results from previous studies for Mexico. 3 and 4 describe the gasoline market in Mexico and the data available for this study. Section 5 presents the econometric techniques used for the treatment of time series and panel data. Section 6 presents the results. The last section concludes.

Short and long run price, income, vehicle stock, and cross elasticities of the demand for gasoline per vehicle were estimated for Mexico with a time series cointegration model for the period 1980–2006 and a panel GMM model with data from 30 states over the period 1993–2004. Approximate elasticities for Mexico City were derived from national estimates and mode shares at the national and local level as suggested by Graham and Glaister (2006). In addition, elasticities for Mexico City were estimated with a panel Within Groups model with data aggregated at the Mexico City borough level for the period 2001–2004, where average gasoline consumption per vehicle was derived from car kilometres and fuel efficiency. Although all models agree on the sign of the elasticities, the magnitude differs greatly. Elasticities change over time and differ between the national and local levels, with smaller price responses in Mexico City. The long run price elasticity in Mexico City is in the range −0.2 to −0.26, while previous gasoline demand surveys mainly based on country data report average elasticities between −0.6 and −0.8. In addition, all models show that changes in public transport fares have negligible effects on gasoline consumption. These values may show the lack of available substitutes such as public transport, or simply that economic agents do not consider public transport as a viable substitute to the car. Estimates of fuel economy elasticities suggest that more fuel efficient technologies have had a negligible effect on gasoline consumption, and the fact that fuel efficiency elasticities are smaller than vehicle stock elasticities suggests that vehicle stock size, rather than its composition, has a higher impact on gasoline consumption in Mexico City. The absolute value of short and long run income elasticity estimates is greater than the absolute value of the price elasticity. Various policy issues are implied by the results of this study. The income elasticity estimates imply that gasoline prices would need to increase faster than GDP growth if the policy objective is to keep gasoline consumption at present levels. Most governments are seeking to reduce carbon emissions, thus this result implies a need for some policy action to actually reduce gasoline consumption. Most developing countries are facing this dilemma of rapid growth in carbon emissions versus demands for increased motorization. Other possible policies have been examined using some of the elasticity estimates from this work. Crôtte et al. (2010) applied these elasticities and other travel demand elasticities to estimate the impact of various pricing policies in Mexico City. This included congestion pricing and environmental taxes to manage demand. Congestion charges provided the largest decrease in traffic and also a large increase in revenue, which could potentially be recycled to support alternative modes or other policies to reduce carbon emissions. While we note the caveats of the data used in this study it provides a first step to analysing these types of policies. The tradeoff between the desire to motorize and the need to reduce carbon emissions will become increasingly critical for developing countries and further more detailed data and analysis will be necessary. This study is a first step in analysing these issues.