Date: Thu, 17 Feb 2000 16:18:45 -0600

Induced Travel Focus at TRB 

Induced travel was a hot topic at the Transportation Research Board's
annual meeting last month, with two sessions devoted to the topic.  

The studies presented provided a range of findings on whether, and to what
extent, adding highway capacity increases driving, with the estimated
amount of induced travel ranging from 6% to 45% of all travel increases in
a region. Two of the studies drew media attention by showing a scientific
basis for the popular notion that 'you can't build your way out of
congestion.'

Lewis M. Fulton of the International Energy Agency found that in Maryland,
Virginia, North Carolina and Washington DC, VMT increased at a rate of 20%
to 60% the rate of increase in lane miles.  

The study also identified causal relationship in that the lane mile 
increases preceded the growth in VMT, and concluded that adding 
roadway capacity reduces the cost of travel and increases mobility, 
but that some or even most of the capacity benefits
will be lost over time.

Robert B. Noland of the Imperial College of Science Technology in the UK
found that lane mile additions account for about 15% of annual VMT growth
in some metropolitan areas, and that the effects are greatest when lane
additions represent large percentage increases over pre-existing capacity. 

His study included estimates of the percentage of travel by 2010 that would
be induced by additional highway capacity in top metro areas.  The
Cincinnati Enquirer characterized his findings this way: "Widening and
building new highways in Greater Cincinnati between 1982 and 1996 accounted
for a 14 percent to 43 percent increase in traffic."

To order a $50 CD-ROM of these and other studies on induced travel, 
call 202.334.3213