(UPI) – People are more likely to reuse hotel towels if they know other guests are doing it too, U.S. researchers suggest.

The study, published in the October issue of the Journal of Consumer Research, found that the types of signs posted in hotel bathrooms had different effects -- signs that focused on the environmental benefits were less effective than signs that pointed out the level of participation of other guests.

Study authors Noah J. Goldstein of the University of Chicago, Robert B. Cialdini and Vladas Griskevicius, both Arizona State University, got a hotel chain to allow them to create a series of different towel re-use cards, which were placed in the hotel's bathrooms.

Some cards read "Help Save the Environment" and others read "Join Your Fellow Guests in Helping to Save the Environment."

Cards that focused on the level of participation of other guests, increased the percentage of participation from 35.1 percent to 44.1 percent.

In a second study, the researchers were able to boost towel reuse even further by placing a sign in the room that said 75 percent of guests in that specific room re-used their towels.

VIDEO: Rickshaws become "conventional"

Delegates attending the Democratic National Convention in Denver are trading in their limos for rickshaws.

The eco-friendly way to get around town is just one of the elements being incorporated into what some are calling the "greenest convention ever."

The pedi-cab bicycle powered vehicles were pre-booked weeks in advance for green-related events surrounding the convention. And owner Greg Duran says he expecst some A-list celebs to pull up to the red carpet in a pedi-cab.

The pedi-cabs will also help alleviate traffic, as the city deals with "Super Bowl" style crowds.

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As firsts go, the event, which ran from Portland, Maine, to the Los Angeles Coliseum, probably would not qualify for the record books. There were stretches without hydrogen fueling stations when the vehicles were carried on flatbed trucks, the longest from Rolla, Missouri, to Albuquerque, New Mexico.

But then one of the goals of the "Hydrogen Road Tour '08" was to demonstrate the need to build more fueling stations if the nascent technology is to develop, said Paul Brubaker, administrator for research and innovative technology for the U.S. Department of Transportation.

There are about 60 hydrogen stations in the United States, and only two are open to the public without prior arrangement.

The industry- and taxpayer-sponsored tour stopped in 31 cities in 18 states. Backers included two hydrogen producers, Air Products and Linde, which hope to become household names if hydrogen becomes a key to transportation.

Catherine Dunwoody, executive director of major tour supporter California Fuel Cell Partnership, said fueling stations will develop first in big cities such as Los Angeles, San Francisco, New York and Washington, D.C.

"There's a lot of curiosity about these vehicles," Dunwoody said near the finish line in Los Angeles on Saturday. "As we got to Allentown, Pennsylvania, people lined up and cheered."

The partnership she heads is based near California's capital, Sacramento, and funded by public and private funds.

"There's a hunger out there for clean, safe vehicles," Brubaker said. "The common refrain everywhere we went was 'Where do we get these cars.'"

For most people, the answer is nowhere soon. Honda Motor Co has begun leasing about 200 FXC Clarity fuel-cell autos in Southern California and General Motors Corp is testing about 100 fuel-cell Chevy Equinox SUVs on the road.

But those deployments, as well as the autos in the road tour, are experimental, since the technology is not ready for showrooms. Carmakers have spent billions on their development in hopes of capitalizing on a public desire to buy cleaner cars and a U.S. push to reduce its dependence on foreign oil.

The United States consumes about a quarter of the world's oil, and imports 70 percent of its crude. Cars and trucks consume 44 percent of oil used in the country and contribute about a fifth of the carbon dioxide emissions. CO2 makes up nearly 90 percent of U.S. greenhouse gas emissions.

Even in a best-case scenario, automakers will only sell about 2 million electric vehicles powered by hydrogen fuel cells by 2020, a study by the National Research Council found.

Cars on the tour came from Honda, GM, Toyota Motor Corp, Ford Motor Co, BMW AG, Daimler AG, Hyundai Motor Co, Nissan Motor Co, and Volkswagen AG.

Linde and Air Products showed off their hydrogen-making machines to the public and at times refueled the autos.

The idea for the tour originated with Brubaker when he watched a Ken Burns documentary, "Horatio's Drive," at the same time that he was reading a biography of Dwight Eisenhower.

The Eisenhower biography mentioned the future president's cross-country trip as a young man, when he noticed long stretches without paved roads. When he was president in the 1950s, Eisenhower started the U.S. interstate highway system.

Burns documented the 1903 drive of Horatio Nelson Jackson who, on a bet, crossed the country in a 20-horsepower Winton car hoping to be the first to make the trip in an automobile. His journey from San Francisco to New York took 64 days.

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The Seattle Parks and Recreation Department reported Thursday that holes had been driven into the trunks of the 70-foot-tall silver poplars and Douglas firs, the Seattle Post-Intelligencer reported. The poison killed the poplars and two of the firs, while the other firs are turning brown.

The trees were planted about 30 years ago, said Mark Mead, a city forester, and they are worth at least $30,000.

Seattle officials recently turned down a request from owners in a condominium complex to trim or remove the trees, Mead said. It was a manager from the Sandpiper Condominiums who noticed and reported the damage to the trees.

A previous attempt had been made to kill the poplars by removing a ring of bark.

Mead said that the poisoning was probably carried out in the past two or three weeks.

Seattle is known for its spectacular mountain and water views, and vandalism of trees by people seeking a better view is fairly common. In one of the most notorious cases, Jerome Farris, a senior federal appeals judge, was ordered to pay half a million dollars 2003 for removing 120 trees that blocked his view of Lake Washington.