The Postal Service has winnowed down the companies bidding to build the next generation of its delivery vehicles - and one of them is offering up an all-electric truck that doubles as a drone launcher.

The agency released a list of pre-qualified sources for the contract April 14, which include Ford motor company, AM General LLC, Fiat Chrysler Automobiles US LLC and Nissan North America, Inc., among others.

But one of the companies - Workhorse Group Inc., - is hoping to make an impression by showing the Postal Service that the future could involve a drone that can deliver packages while the mail carrier works their normal route.

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The electric delivery truck is called "Workhorse" while the drone that carries the packages is called "Horsefly" and is a product of a years-long partnership between the company and the University of Cincinnati, which has an unmanned vehicle research program.

"We feel very confident that our integrated drone technology on top of our electric truck is the best solution for the Postal Service as well as give them the lowest total cost of ownership for their truck needs and their future drone needs," said Duane Hughes, director of sales at Workhorse Group, Inc.

The mail carrier gets to a neighborhood to begin delivering mail or other packages. Meanwhile, the drone delivers a package either on its own or controlled by a pilot remotely to another address a mile or two away, saving the mail carrier time and allowing them to reach more addresses.

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Cutting down on the time it takes the Postal Service to complete a route and delivering more packages during that time could save the Postal Service a lot of time and money, according to Hughes. The fifth generation of the Horsefly drone - its most current incarnation - weighs about 15 pounds and can carry a 10-pound package in extendable cages that lock together during flight.

The drone can fly up to 50 miles per hour, but will spend most of its time flying at about 35 miles per hour, according to Hughes.

The drone also comes with automatic stabilizers to make flight easier, and can automatically dock on top of the truck. It then charges itself using the electricity in the electric truck. Because it is attached to the truck and driven into the neighborhood, it removes the issue of a drone flying 30 or 40 miles to deliver a package from a warehouse, according to Hughes.

There is a lot at stake for the manufacturer that wins the contract. They would provide 180,000 vehicles for $25,000 to $35,000 per vehicle – making the potential contract worth more than $4.5 billion.The proposed vehicles would need to last at least 20 years, carry a minimum of 1,500 pounds and pass all safety and emissions requirements across the country.

The Postal Service also wants lower maintenance requirements and better fuel economy than its current fleet, as well as design flexibility to allow for the incorporation of future technology, according to the agency.

It is the lowered maintenance costs and the look toward the future where Hughes thinks Workhorse Group, Inc., shines. He said the electric trucks would save the Postal Service significantly on maintenance costs, while the drone platform incorporates a fast-evolving technology that will only grow over the next few years.

"As the Postal Service moves further into the package delivery business we have to look at it from the perspective of 'we don't' want a truck to just last 20 years, but how is the business going to look in five, 10, 15 years out?'" Hughes said.

The electric vehicle has a range of 50 miles to 100 miles, depending on whether it recharges while on its route using a small generator included inside the vehicle. Since almost all Postal service routes fall within that range, that would alleviate the "range anxiety" that could come with electric vehicles, Hughes said.

Software included in the truck also tracks battery usage and depletion. Instead of letting the battery drain too far the generator replenishes it in small amounts, lengthening the lifetime of the battery.

The Postal Service plans on issuing a request for proposals in May, and the agency would then award several companies a contract to test a prototype and then choose the best from among them, according to the Postal Service.

The agency plans on picking the suppliers for the prototype in July, 2015 and will then test the prototypes through September, 2016. The final supplier will be selected in January, 2017, according to the Postal Service. The Postal Service would start receiving and using the vehicles one year later.

Kelly Cohen, professor of aerospace engineering at the University of Cincinnati, has helped lead the research and development of the Horsefly drone system in partnership with Workhorse Group, Inc.

The drone automatically adjusts to a wide variety of air speeds and weather conditions, according to Cohen, using advanced software similar to large aircraft. He said the team has heavily emphasized overall safety and has built redundant motors and controls into the drone.

The current generation of the Horsefly comes with a metal cage to hold up to 10 pounds in packages.

Photo Credit: Workhorse Group, Inc.

But even as his team works out the technical challenges with the drone delivery system, he said the biggest challenge would be expanding drone usage and analyzing the data of thousands of drone deliveries happening at once.

"The limitations are more on the side of integration into the air space and that concerns security and overall safety. How do we control 100,000 drones in the air flying at once? Cohen said.

He said he could see the system being rolled out slowly, starting in specific neighborhoods and expanding outward. There would then be enough data to see what possible safety concerns there would be and to adjust accordingly, Cohen added.

He said the team has been testing larger and more complex delivery drones, including larger models that can carry up to 30 pounds at once. He said as the technical issues with drones are solved and the costs begin to come down, there will be more and more companies and people calling on drones as a solution to various problems.

"What we try to do is look at the way people operate today and say what if we bring about a technological solution, what benefits would we get," Cohen said. "The US can no longer sit back and say I don't want any of this because other countries are really enhancing their skills and capabilities in this area."