Re: Closing Roads Might Cut Congestion, Study Says (fwd)

hancock4@xxxxxxxxxxxx wrote:

On Oct 13, 3:46 am, John Lansford <jlnsf...@xxxxxxxxxxxxx> wrote:

Induced traffic is the boogeyman of road opponents, used to justify
their resistance to adding new routes.  Studies have shown that
induced traffic rarely adds more than 10-15% to the overall traffic
volumes, which is a fairly insignificant number.  What they tend to
lump in with induced traffic, however, is diverted traffic, which is
where traffic using less capable routes suddenly use the newer, less
congested road when it opens.

That is not necessarily a bad thing.

Obviously different new roads have different impacts.

I'm not sure I would call "10-15%" insignificant, especially if
existing local roads are already congested.

You're misunderstanding what I said. Induced traffic is typically
calculated for the main road, not the side street, where diverted
traffic may be more of the volume than you think. A 15% increase in
total expected traffic volumes is fairly meaningless when discussing
capacity issues.

Speaking in very general terms (I do not have specific volume counts),
let's take the suburban Phila "Blue Route" as an example. It was
supposed relieve severe congestion on parallel local roads, but AFAIK,
local roads remain lousy (my own driving experience and radio
reports). The Blue Route itself is jammed at rush hours.

The route has clearly opened up new travel possibilities. There has
been extensive commercial development near it for which IMHO the road
is responsible. When it is not jammed, it offers a high speed
connection between many key points in the region not prevously
available at all. IMHO all that is induced traffic.

But how much of that total traffic volume is induced? Or, was the
expected volume of traffic so heavy that it was going to be under
capacity when opened? How about diverted or latent traffic? None of
those are "induced" but like I said earlier, anti-road types like to
throw out that term to justify their positions.

I do not know what percentages of the Blue Route represent "induced"
and represented "diverted". I strongly suspect the percentages vary
by time frame. [One thing about oft-quoted traffic counts that bother
me is that they are not broken down by time-frame--rush hour, weekend,
etc.]

Then we're down to opinions on this subject.

John Lansford, PE
--
John's Shop of Wood
http://wood.jlansford.net/
.

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