Engineering Economic Analysis

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Incremental Analysis

Tapping into Controversy

When New York's Tappan Zee Bridge opened in 1955,it seemed big enough to handle any

amount of traffic that was likely to come its way. The bridge spanned the Hudson River at

a crossing in Westchester County, well north of New York City, near.towns seemingly so

removed from Manhattan that they were referred to as "satellite communities." Invoking

visions of westward expansion and unpopulated vistas, state government officials proudJ.Y

told voters that the $81 million bridge project would open up "new frontiers."

During its first full year of operation, the bridge' carried only 18,000

vehicles per day, far below its design capacity of 100,000.By 2000, the satellite

communities were called "suburbs," and the Tappan Zee Bridge was being used

by 135,000 vehicles every day. That number is expected to increase to 175,000

over the next two decades.

Clearly, something must be done to ease the growing congestion on ~e

bridge. But what? The bridge's usable space has already been expanded once by

converting a large median strip into a reversibletraffic lane. And the bridge itself

is nearing the end of its useful life, which originally was intended to be 50 years.

Upgrading the existing bridge would likely cost over $1 billion and would

not adequately alleviate traffic congestion. Building a new bridge could cost as

much as $4 billion dollars-quite a jump from the original price tag.

Why so costly? Inflation explains part of it, of course. The original Tappan

Zee Bridge would cost almost $600 million in today's dollars. The new bridge

would also be bigger. It would have eight lanes instead of six, a 33% increase.

But much of the cost would come from additional expenses that could not

have been contemplated 50 years ago. Backers of the original bridge happily

predicted that it would increase property values and attract new homebuyers

to "outlying areas." And so it did. But nowadays, this effect is called suburban

sprawl, and most taxpayers want less of it, not more. Many local residents

fear that enlarging the bridge would simply encourage even more traffic-soon

leading back to the same quandary they are now in.

To address these concerns, some government officials have suggested in-

corporatinglight-rail tracks and bus lanes into the new structure, in an attempt to encourage

greater use of mass transit. Others have suggested installation of a more sophisticated toll-

collection system that would give discounts to off-peak travelers. Any such additions to the

bridge would considerably drive up the cost of construction:

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