Daniel Convissor's Website

The feedback parameters such as land use factors and mode of travel exert an influence on gasoline use far in excess of the fuel efficiency of vehicles as determined by traffic conditions. In other words in the congested but denser and more compact central and inner areas travel distances are shorter for all modes and there is greater use of public transportation, walking and cycling. In outer areas where densities of development are low, travel distances are long and a much higher proportion of travel is by automobile with less public transportation, walking and cycling....

The traffic engineering model is actually promotive of increased gasoline use in cities, i.e. if gasoline conservation is sought through programmes which aim at "blanket" increased in average speed (e.g. freeways and other road building activities such as lane increases), these will almost certainly result in less fuel-efficient city overall. A major reason for this is that such programmes push a city further and further towards total reliance on the automobile and away from a balanced transportation system....

[A] survey attempted to find out how many people might transfer from transit to cars should congestion be significantly reduced or eliminated in the corridor. The survey shoed some 17.2% of bus passengers and 11.0% of train passengers would transfer if the congestion was eased. It was calculated that if only half of these passengers actually did transfer to cars, the extra gasoline use would be enough to cancel out the savings from a computer- coordinated set of traffic signals along the corridor designed to smooth out traffic flows....

A study of the fuel and time implications of freeway speed limits in Perth indicated that optimal fuel efficiency occurs at cruise speeds of 55 k/h [35 m/h].... It was shown that policies which encourage further increases in cruise speeds such as increasing speed limits, freeway building and road widening will be counter-productive for energy conservation....

....vehicles driven in the Perth central area at 33.8 k/h [20.3 m/h] average speed have 17% to 27% more hydrocarbon and carbon dioxide emissions respectively per kilometer of travel relative to the average for Perth, residents of the area actually generate 19% to 21% less total CO and HC respectively due to their smaller use of the automobile and greater use of other modes. Conversely in outer areas there is a positive benefit in terms of emissions from vehicles with the average speed of 52.2 k/h [30.3 m/h] yielding 9% to 16% lower emissions per kilometer (HC and CO respectively) than the average for Perth. However, residents of the outer suburbs actually generate some 24% to 27% more CO and HC respectively than the average for Perth residents due to their longer auto travel distances and less use of other modes.... In other words higher density land use, a greater need for cars, longer travel distances and reduced use of other less polluting or pollution free modes. The benefits gained in terms of less polluting traffic streams are overwhelmed by the sheer amount of extra travel and the resulting bulk of emissions....

The range of bus speeds for the cities is remarkably small tending to be around 20 to 21 k/h [12 m/h] and never exceeding 25 k/h. On the other hand, those cities with significant rail-systems tend to have much faster overall transit operating speeds because rail systems have average speeds typically above 40 k/h [24 m/h] and up to 55 k/h [33 m/h] in some cases. Such systems provide very good competition to the automobile for speed of access.... Rail systems again emerge as being crucial factors in promoting a more efficient and balanced transportation system. In each city where there is a significant rail system the average speed of automobiles and the overall average speed of transit are much closer to one another and in quite a few cases transit actually exceeds the automobile. In cities where buses are the major form of public transit, average transit speeds are generally half that of the automobile and markedly unbalanced transportation systems are the result (e.g. Houston, Phoenix and Denver)....

The relatively simple methods used to provide traffic engineering cost-benefit analyses of new roads are not realistic.... Fuel savings (and emissions reductions if they are included) should no longer be part of urban road project justification since it appears that new roads that improve traffic speeds actually generate higher fuel use and more emissions overall....

The individual city dweller has a key role to play and it is often ignorance or dare I say, selfishness on the individual's part that can be a key force in promoting less balanced cities.... If the aim is to maximize private environmental amenity then the result is often public squalor. It is an onus on every city dweller to realize that they are individuals within a system and must of necessity make some sacrifices for the good life of the city as a whole.... However, what may appear at first to be a sacrifice or denial of something soon turns out to be an improvement in the quality of urban life for all.... The potential for building a good urban environment is only as great as the vision and the will to do it.

--DC

This research was also mentioned in the AASHTO International Transportation Observer