The government is car shopping.

The United States Postal Service has issued an open call to automakers to bid for a commercial van contract as the agency works to launch a new delivery fleet by 2018, Automotive News reported.

According to the initial specifications, the USPS contract would comprise 180,000 vehicles at $25,000 to $35,000 each, costing a total of $4.5 billion to $6.3 billion.

The current fleet of Long Life Vehicles comes from the aerospace company Grumman Corp., which was later purchased by Northrop; the trucks have had numerous problems during the last 30 years that include faulty doors, leaking windshields and low fuel economy.

"At some point, the fleet has to be dealt with," Tom Day, chief sustainability officer at the Postal Service, said at a 2014 hearing of the U.S. Postal Regulatory Commission, as quoted by Automotive News. "The wheels are just going to fall off at some point in time. Whether we refurbish it or replace it, something has to be done."

USPS will meet with potential bidders next week in Washington, planning to select carmakers this summer to build prototypes for testing in 2016. The plan is to award the contract in early 2017.

While a government project typically isn't that profitable, a contract as large as the USPS fleet could be tempting to automakers such as Ford Motor Co., Daimler AG and Fiat Chrysler Automobiles, according to Automotive News.  

One hurdle for the company that takes on the project will be developing a vehicle with right-hand drive, which allows postal workers to reach through windows and put mail into mailboxes on the side of the road. In other challenges, USPS is also looking for alternative power options as well as modifications that will better fit the average mail carrier's everyday routine. 

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