the criteria used to make these temporal distinction differ across studies. As a general rule,anything less than 1 year is uaually regarded as short run. Other studies are based not so strictly on time but no the type of change involved. Thus, for instance Trace 1998 and de Jong and Gunn 2002 allowed only for mode choice change in the short run,but included all other behavioural change in the long run(destination choice,travel frequence choice,land uce change)
Table 8 also presents the means of road traffic-related elasticity estimates either calculated by us for this survey or taken from other review articles. car ownership mean elasticities are also quoted , although it must be recognized that these value are based on very few estimates and this necessarily tempers the degree of confidence of these values. thoughout ,this review has stressed that are accepted as being indicative of broad orders of magnitude , some interesting themes can be drawn out.
First , the review clearly shows that growth in the standard of living is crucial in explaining increasing road traffic demand . the level of car ownership is heavily dependent upon income as is the demand for car travel and fuel consumption. table 8 shows that the mean elasticities of car ownership and car km with respect to income are very similar in both the long and short runs , but the fuel demand elasticities take higher values. perhaps this support thehypothesis that as incomes grow, as well as buying more cars and thus creating more traffic, consumers are moe likely to purchase larger cars and cars that are less fuel-efficient.