BOSTON/SAN FRANCISCO (Reuters) – Some environmentally focused investors are not ready to buy into Lyft Inc or Uber Technologies Inc, worried about the climate impact of this year’s two most closely watched initial public offerings.

Both companies hope to push people away from car ownership and promote shared and sustainable transportation services, among their many ambitions that have already reshaped traffic in major U.S. cities.

Lyft began trading on Friday and its larger rival Uber will kick off its IPO this month, though neither has shown itself to be profitable and shares of Lyft sank below their initial price of $72 on Monday.

Academics and city planners are still studying whether the companies will help reduce carbon emissions by making better use of existing vehicle fleets, or increase them by clogging traffic and diverting riders from trains and buses.

But even as the companies argue congestion has many causes including growing city populations, some investors cite early indications that ride-hailing technology puts more, not fewer, cars on the road.

“As far as I can tell, they’re actually putting more cars into the congested areas, and they’re pulling business out of the transit systems,” said Murray Rosenblith, portfolio manager of the New Alternatives Fund, which aims to make socially responsible investments.

“This is not an area where New Alternatives is going to get engaged,” Rosenblith said.

Joshua Brockwell, a director at Azzad Asset Management, which also factors environmental issues into investment decisions, said both companies also face the issue of drivers “deadheading,” or driving around in between fares.

While both also aim to reduce private car ownership, he said, “that’s a not an eco-friendly goal in and of itself. It’s overall ‘miles traveled’ and carbon emissions that count.”

Representatives for several other well-known climate-focused investors said they do not buy IPOs or were not ready to weigh in on ride-hailing, including Green Century Funds, Boston Common Asset Management and Parnassus Investments.

Research shows mixed results. A 2017 University of California at Davis study found ride-hailing boosted use of commuter rail but pulled people away from buses and light rail. In addition people often used the apps to take trips they previously made by walking, biking, taking public transit or not taking at all.

A study by the San Francisco County Transportation Authority found that about half of new congestion in San Francisco from 2010 to 2016 was from ride-hailing. Average speeds in the city stood at 20.9 miles per hour at the end of the period, researchers found, 3.1 miles per hour slower than at the start. bit.ly/2EsU7cg

Drivers for Lyft and Uber often travel far to reach urban areas before they even turn on the app. It is common for drivers from California’s Central Valley to drive close to 100 miles (160 km) to San Francisco in search of more lucrative fares.

Lyft executives including Chief Policy Officer Anthony Foxx said that the company has taken other steps to combat congestion such as showing bus arrival times on its smartphone app and investing in bicycles and scooters. Lyft also says it spent millions of dollars on carbon offsets in 2018, and supports transit infrastructure.

“We are on a long path. We didn’t get to this level of congestion in our cities overnight,” Foxx said in an interview with Reuters.

Uber did not make executives available to comment, but the company has made its own commitments to bikes, scooters and other sustainability initiatives. Its CEO Dara Khosrowshahi in September promised $10 million to study ideas such as congestion pricing to speed traffic.

One opportunity is that Uber and Lyft could help drivers buy more expensive electric cars, which have a lower cost per mile. Accelerating the shift to electric could win over Seb Beloe, head of research at WHEB Asset Management in London, another investor focused on sustainability, he said via email.

But he avoided the Lyft IPO and worries the service and Uber will diminish public transit. As things stand, “we think that the case is not yet compelling” for the companies, Beloe said.