Two auto industry leaders see electric vehicles, car sharing, and alternative fuels like biofuels and compressed natural gas transforming the passenger vehicle landscape in the years to come.

Mark Reuss, president of General Motors of North America, the world's biggest automaker, and Andrew Taylor, CEO of Enterprise Holdings, the largest car rental company, said they must be adaptable to the changing government, public and customer sentiment on all those possibilities.

“We have to be very flexible,” said Taylor during a 45-minute discussion Monday at the Donald Danforth Plant Science Center in St. Louis.

With more charging stations needed and traveling range still a concern, It's too early to say where electric vehicles will go, he said.

Reuss, whose company makes the hybrid Chevrolet Volt, also sees promise in electric vehicles, even though he thinks they're not for all. While GM will still be providing utility, high performance and other features the company is known for, he sees future vehicles being lighter and filling other needs.

Electric vehicles aren't the only route to the more sustainable future Reuss and Taylor envision.

“We’ve got all kinds of options with CNGs (compressed natural gas),” Reuss said, though he cautioned that even as the infrastructure for CNGs has developed, the tools to efficiently get CNGs into the car has lagged. And biofuels are another promising avenue, he said.

Both GM and Enterprise have also dipped into the car sharing business. Peer-to-peer ridesharing service RelayRides has a partnership with GM subsidiary OnStar that also uses technology helpful for the business such as unlocking doors through a mobile phone.

Illustration of electric vehicle provided by iQoncept via Shutterstock

A separate GM announcement Tuesday highlighted another sustainability initiative. The company said all its future North American construction sites will use GM's green construction practices, and pointed to a $200 million stamping plant in Arlington, Texas as one of five construction sites that's helped recycle 150,000 tons of waste through a recycling and energy efficiency program.

The company last year announced 32 investments totaling nearly $5.5 billion, many of which will be part of the initiative. Requirements include using curtains and barriers to reduce airborne particles like dust and dirt from entering the atmosphere, using rechargeable batteries and segregating materials like metal, plastic, glass and concrete for recycling ease.

The Arlington facility reused construction byproducts including 120,000 cubic yards of clean soils for site-balancing activities like constructing a berm. It also turned 10,200 tons of recycled concrete into base material for pavement and a finer mixture used to support pipes in trenches. The facility, home to the Chevrolet Suburban and Tahoe, GMC Yukon and Cadillac Escalade, has also recycled 112.5 tons of asphalt and 25.6 tons of steel and other metals.