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It is projected that 25 million km of new paved roads will be developed globally by 2050 - enough to encircle the planet more than 600 times. Roughly 90% of new roads will be built in developing nations, frequently in tropical and subtropical regions with high biodiversity and environmental values. Many developing nations are borrowing from international lenders or negotiating access to their natural resources in order to expand their transportation infrastructure. Given the unprecedented pace and extent of these initiatives, it is vital to thoroughly assess the potential consequences of large-scale road and highway projects. In appropriate contexts and locales, new roads can promote sizeable economic and social benefits. If poorly planned or implemented, however, new roads can provoke serious cost overruns, corruption and environmental impacts, while generating sparse economic benefits and intense social and political conflict. Using examples from developing nations, we identify risks that can hinder road projects in wet and dry tropical environments. Such risks, we assert, are often inadequately considered by project proponents, evaluators and the general public, creating a systematic tendency to overestimate project benefits while understating project risks. A more precautionary approach is needed to reduce risks while maximizing benefits of new road projects in the tropics.

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