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Adding Highway Lanes Will Reduce Congestion Despite The Skeptics

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Will adding lanes to a highway reduce congestion? That argument has been
made in my town, and that was an argument many years ago when I lived in
Florida and widening was proposed for the road to a beach. The argument
usually does not stand up, though. People running a business where
traffic matters should understand the issue.

Residents in a fast-growing city may see additional lanes become
congested just like the road used to be. But the proper question is not,
“Did congestion improve when lanes were added?” Instead we should ask,
“How does actual congestion compare to what it would have been without
the additional lanes?” If an area has strong population and job growth,
then more vehicles traveling is natural. If the lack of congestion
relief comes simply because the region grew, then ask what the traffic
would have been without the extra lanes.

Let’s imagine a city with no growth, at least not regarding travel from
the city center to the suburbs. Suppose there are two alternative roads
north, Route 1 and Route 2. Now Route 1 gets another lane. Could
congestion on this road be just as bad as before the additional lane was
built, even with no growth of population or employment? If Route 1 now
has the same congestion as before, the total number of cars traveling on
Route 1 is higher. What induced those people to drive on Route 1?
Previously they had weighed the alternatives: Route 1 or Route 2. Why
would anyone shift from Route 2 to Route 1 if congestion is the same as
before? That implies irrational behavior. But even if true, the
additional lanes on Route 1 have reduced congestion on Route 2.


More likely, some people start using Route 1 instead of Route 2
expecting less congestion. Expectations adjust to reality over time and
people are taking the best possible route given their starting point and
destination. A balance is reached where congestion on both roads is
lower than before the lane addition.

The idea that extra lanes don’t relieve congestion comes because places
that add lanes tend to be growing. That growth will increase congestion
if new capacity is not built. But people tend to see simply that extra
lanes are now as congested as the old lanes before extra construction,
without asking how the extra people would have gotten around with the
old number of lanes.



Sometimes, though, extra lanes will spark more travel. In the case of a
road to the beach, an extra lane might induce people to take trips they
otherwise would not have taken. Imagine a large number of inland
residents thinking, “I’ll drive to the beach if I can get there in less
than 45 minutes.” The volume of beach-goers stabilizes so that a trip
takes exactly 45 minutes.

When an extra lane is added, at first trips take just 20 minutes. Many
people learn of this and head to the beach. The volume of traffic
stabilizes at a level leading to a trip taking 45 minutes. Congestion is
the same as before. The person who lives at the beach sees no benefit,
but look at the inland residents who now go to the beach more often. If
a two-lane road was increased to four lanes, then twice as many people
are able to go to the beach. That’s a social benefit in itself. People
clearly want to go to the beach. Now more of them are able to do what
they would like to do.


Opponents of automobility argue that low congestion—fast highway
speeds—will lead more people to drive rather than take public transit or
work from home. That’s likely true, though the magnitude in a modern
metropolitan area will probably be fairly small.

To the extent that people do respond to the reduced congestion by
traveling more, that reflects those people’s preference for how they
live their lives. Whether this is better for the community as a whole or
not, businesses that depend on traffic will gain. Business leaders
working in a local market must understand the area’s underlying growth.
And for some businesses, traffic and congestion heavily influence
customer traffic.

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Adding Highway Lanes Will Reduce Congestion Despite The Skeptics Popping Mad <rainbow@colition.gov> - 2025-12-25 09:45 -0500

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