The lawsuits contend the agency has underestimated the environmental impact of its ‘next-generation’ vehicles, which get 8.6 mpg.

Sixteen states, the District of Columbia and environmental activist groups are suing the U.S. Postal Service to block its purchase of 148,000 gas-guzzling delivery trucks over the next decade, alleging the agency has vastly underestimated the vehicles’ costs and adverse ecological impact. The suits brought by the state attorneys general, Earthjustice and the Natural Resources Defense Council contend that the mail service relied on faulty assumptions and miscalculations to justify spending as much as $11.3 billion on gas-powered vehicles that get 8.6 mpg, which is only incrementally better than the 30-year-old vehicles now in use.

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