(Bloomberg) -- Taxis aren’t the only ones that may bestressing out about Uber Technologies Inc.Transactions from the ride-hailing startup have surpassed rentalcars among American professionals, according to Certify, the second-largest provider of travel andexpense management software in North America.

Uber accounted for 43% of ground transportation transactionsexpensed through Certify last quarter, while rental cars had 40%.Ride-hailing services, with Uber at the forefront,overtook rental cars for the first time in the fourth quarterof 2015 and have since widened their lead, according to a study byCertify published on Thursday.

Related: Ride-sharing services to have little impact on carsales, survey finds

While an Uber or Lyft Inc. fare costs much less than theaverage rental car booking, the data show thechanging preferences among business travelers. Rental cartransactions have fallen 15 percentage points in two years. Thedecline isn't quite as steep as the one experienced by taxis,which fell 23 percentage points over the same period. Taxisaccounted for 14% of ground transportation transactions inthe first quarter of 2016.

It comes down to convenience

"It really comes down to convenience," said Robert Neveu,president of Certify. "The ability to hail and pay efficiently—thatconvenience factor is huge, and we’re seeing it change the habitsand behaviors of our users."

Many travelers, who previously would have rented a car forconvenience even when they didn't expect to drive much, arechoosing Uber for those shorter trips, said Hamzah Mazari, ananalyst at Sterne Agee. Investors are concerned, hesaid. Shares in Avis Budget Group Inc. and HertzGlobal Holdings Inc. are each down at least 36% thisyear. "Uber definitely has an impact on the car-rentalindustry," Mazari said.

Rental car companies have been looking for ways to go beyonddaily rentals to travelers. Since Avis acquired Zipcar in 2013,Enterprise Holdings Inc. has introduced a Carshareprogram of its own to offer customers hourly rentals. Hertzsaid this month that it led an investment round in Luxe ValetInc., a San Francisco startup that provides on-demand parkingservices via a mobile app.

Some automakers, which have traditionally viewed rentalcars as a way to expose their vehicles to prospective customers,are getting into the ride-hailing game. General Motors Co. said in January it wouldinvest $500 million in Lyft, the second-biggest U.S.car-booking company. As part of their partnership, GM and Lyftare developing short-term car-rental hubs in some U.S. cities.Mercedes-Benz parent company Daimler AG bought Mytaxi, an Uberrival in Europe, in 2014.

Related: BMW challenges Uber in U.S. with its ownride-booking service

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