SideCar and Lyft slice that market finer, monetizing an empty seat by letting owners tote along fee-paying passengers on routes they may already be taking.

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Anyone over age 18 may apply via video for a seat on board the rocket, but there is an application fee.

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The Department of Transportation will also propose doubling the bump fee that airlines must pay to travelers who buy tickets but lose their seat due to overbooking.

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Other heavier fliers argue while tall passengers pay a fee for legroom, the fees are only a fraction of the price of a entire seat.

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