اثر قیمت بنزین در اقتصاد شهری: از انتخاب مسیر به تعادل عمومی

RELU-TRAN2, a spatial computable general equilibrium (CGE) model of the Chicago MSA is used to understand how gasoline use, car-VMT, on-the-road fuel intensity, trips and location patterns, housing, labor and product markets respond to a gas price increase. We find a long-run elasticity of gasoline demand (with congestion endogenous) of −0.081, keeping constant car prices and the TFI (technological fuel intensity) of car types but allowing consumers to choose from car types. 43% of this long run elasticity is from switching to transit; 15% from trip, car-type and location choice; 38% from price, wage and rent equilibration, and 4% from building stock changes. 79% of the long run elasticity is from changes in car-VMT (the extensive margin) and 21% from savings in gasoline per mile (the intensive margin); with 83% of this intensive margin from changes in congestion and 17% from the substitution in favor of lower TFI. An exogenous trend-line improvement of the TFI of the car-types available for choice raises the long-run response to a percent increase in the gas price from −0.081 to −0.251. Thus, only 1/3 of the long-run response to the gas price stems from consumer choices and 2/3 from progress in fuel intensity. From 2000 to 2007, real gas prices rose 53.7%, the average car fuel intensity improved 2.7% and car prices fell 20%. The model predicts that from these changes alone, keeping constant population, income, etc. aggregate gasoline use in this period would have fallen by 5.2%.

How does the urban economy respond to an increase in the price of gasoline? Since the mid 1970s econometric studies have measured the price elasticity of the demand for gasoline, using state, national and international cross-sectional or time series data. These studies tell us how a change in the gasoline price would affect total vehicle miles traveled (VMT), changes in the stock of vehicles owned and the average fuel economy of cars being operated. From these studies, we know the probable ranges of the price elasticity of the aggregate demand for gasoline, and the “rebound effect”, the propensity to drive more as the fuel economy of cars improves in response to higher gasoline prices.

A spatially disaggregated computable general equilibrium approach is important in understanding how the price of gasoline affects aggregate gas consumption, VMT and on-the-road fuel intensity (GPM) because it determines these effects from basic microeconomic foundations rather than from reduced form regression models. From a methodological standpoint, since this is the first spatially disaggregated CGE model study of gasoline consumption, we believe it serves as a complement to the many econometric studies and points the way to future studies.