If it was decided to not invest in lock extensions, traffic on the waterway would likely not grow much beyond current levels because of the costs associated with congestion. Thus, although uncertainty about the future value of infrastructure investment should not be a reason for taking no action, infrastructure investments such as the Gander Airport and improvements to navigation such as the Tennessee –Tombigbee waterway make it clear that ill-conceived investments can be costly.

Improving the efficiency of current use lessens congestion and pushes back the time when a decision must be made on infrastructure expansion. As the Gander Airport example shows, delaying a decision for a few years could show that the investment should be designed differently or even is unnecessary. As soon as the Boeing 707 demonstrated that it was cheaper, more reliable, and much preferred by passengers, the airlines scrambled to buy jets and shed their propeller aircraft from their transatlantic traffic. Had they waited a few years before making their expansion decision, Gander planners would have seen that airport traffic was about to decline precipitously.

There are costs, however, to waiting for more information, just as there are costs to building a project on the basis of current information. If traffic continues to increase, waiting to build a project means that users will have to bear the costs of increased congestion for years. If traffic does not increase, as in the Gander example, construction costs will be mainly wasted.

Society needs a prudent rule for deciding when there is sufficient information to stop waiting and to start building. Such a rule involves tradeoffs between the social losses from building when it is not warranted, and delaying construction beyond the points where new capacity is needed. The decision also requires an estimate of the likelihood that the additional capacity is actually needed on the basis of currently available information. The latter is a technical decision; this committee can lend advice to the Corps on the estimation. The former is a value judgment that Congress—not the Corps—must make.

Extra throughput could be squeezed out of the current locks by improving congestion management. Although scheduling tows to arrive at the locks is difficult, valuable steps can be taken. The level of traffic on the Upper Mississippi River is not uniform over the navigation season. Smoothing traffic would significantly reduce congestion and delays. Nonstructural measures such as a scheduling system, congestion pricing, and tradable permits will also initiate smaller and far fewer environmental impacts than structural measures such as lock extensions. They are therefore more consistent with strategies for the sustainable development (promoting improved traffic flow and environmental restoration) of the Upper Mississippi River and tributary system.

When infrastructure investments are prudent, it is important to find the appropriate scale for the investments. Social resources are wasted by building a small structure that must be replaced in a few years, or by building a structure whose capacity is not needed. Thus, a careful analysis of the range of possible future demands and ways of accommodating them is needed.

The nation has undergone a profound shift in how environmental resources are regarded and valued. For example, the prospect of removing four large federal hydroelectric power dams on the Snake River in the Pacific Northwest, in order to restore salmon runs and the environment, has been discussed at the highest policymaking levels; several other U.S. dams have already been removed. These changes are occurring because environmental consequences have in some instances turned out to be worse than expected, and because society today places greater



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