Jim Hanni just knows what the industry numbers tell him: Green is becoming a factor in the travel industry.

Not green as in money — though cost is always crucial — but, rather, the environmental type of green.

Hanni, the executive vice president of the Kansas region and public affairs for AAA at 3514 Clinton Parkway, says the green trend is seeping into the travel industry, slowly but surely.

“More than eight out of 10 travelers consider themselves to be environmentally conscious,” Hanni says. “Four in 10 say they would definitely or probably select an environmentally friendly travel supplier if they were aware of the supplier’s commitment to the environment.”

The problem, Hanni says, is that there aren’t any industry regulations on wording in regards to “green” or “eco-friendly” travel.

Because of this, John Novotny of Travellers, Inc., 831 Mass., says that in many ways, being green while traveling is a personal choice the traveler makes when doing things like renting a hybrid car or asking hotel staff not to waste water putting his or her sheets and towels through the wash daily.

“I think people that are conscious of the environment actively, are doing things themselves, when they travel, too … in other words, they just take their same good habits they have at home and apply them on the road,” Novotny says. “I would bet their own living habits extend to them as they travel.”

Enter a new study by a group of scientists who have put together a green guide to travel. The guide, by the Union of Concerned Scientists, outlines ways to travel while making the smallest carbon footprint possible.

The researchers compared the amount of carbon dioxide — the chief heat-trapping gas that drives global warming — from driving, flying, traveling by train or bus, and also compared per-person emissions for solo travelers versus those traveling in pairs or as a family of four. Here are some of their findings:

• For trips of more than 500 miles, if you’re traveling solo or with one other person, it’s greener to fly direct in coach than to drive, according to the group.

• First-class seating takes up more space than coach seating, so the average first-class passenger on a domestic flight is responsible for generating twice as much carbon as someone seated in coach, the group says. Budget airlines with no first-class seats can lower a plane’s per-person emissions 10 to 15 percent.

• Compared with flying coach, a couple traveling on a bus will cut their trip’s carbon dioxide emissions 55 to 75 percent, depending on the distance traveled. Compared to even a fuel-efficient hybrid car, a bus trip would cut a couple’s trip emissions nearly in half. Bus travel is usually less expensive than flying and for a solo traveler, can be cheaper than driving.

• Trains emit 60 percent less carbon per passenger-mile than a typical car with a single occupant. And compared with a 500-mile trip on a small jet plane, a train emits roughly 30 percent less carbon. Trains also can save money by dropping you in city centers, so you don’t need to get a taxi or rental car to get into town.

• The type of car you use for a road trip makes a big difference. An SUV emits nearly four times the amount of carbon dioxide emissions of a highly efficient hybrid such as a Toyota Prius, and uses nearly four times the amount of gas.

• Traveling off-peak can also lower your carbon footprint and travel bills. Spending less time in traffic means better mileage and lower fuel bills; flying off-peak means your plane won’t be wasting fuel in a holding pattern and your ticket could be cheaper.

— The Associated Press contributed to this story.