It has now been accepted practically everywhere except Australia that amplifying roads generates extra traffic. The most accessible discussion of this is in the 1995 S.A.C.T.R.A. report from England. A 1991 report Road Traffic - Future Directions by Booz-Allen and others warned that Sydney faced 600% more time lost due to traffic congestion each morning peak by 2011 if current road-building practices continued (the report did not canvass the question of oil supplies). So far, the practices have not merely continued but blossomed.
Australian road authorities, including the N.S.W. R.T.A., officially have a policy of Travel Demand Management ("TDM"), set out in the book TDM Guidelines, ISBN 085588-460-6. However, they lack the will to implement anything effective, preferring instead to encourage telecommuting and other mild measures which can only remove such small amounts of demand that any road capacity released is immediately taken up by new and/or lengthened trips. Authorities seem content to let private vehicle-kilometres per day increase by about 3% per year.
The general finding of research available to Action for Public Transport is that people adjust their lives so as to spend a fixed amount of time per day travelling. Thus, the effect of higher-speed travel is manifest mainly in people travelling further!
This explains why Action for Public Transport's policy on road pricing is that the most effective costs in controlling travel demand are time costs. If you want to make most people use public transport, then it has to be competitive in point-to-point total travelling time, including any waiting, with other travel modes. In some cases, it may be necessary to slow down car travel. A cheap way of deterring car travel, especially long trips, is to let road congestion propagate, i.e. desist from building new or faster roads or amplifying old ones.
Our road-builders seem to have lost touch with the distinction between mobility and access. The former is simply measured by how much movement there is, in kilometres per day. The second is more difficult; it is an indication of how many useful destinations people reach per day and it is affected by how far away those destinations are and whether there are good transport routes between them.
If your city is planned properly, there should be ample access without excessive mobility. Good cities have good access without needing large amounts of mobility; the same cities are laid-out in a way which complements public transport.
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