Voters in November approved new sales taxes to keep the city’s bus system alive, and now city commissioners are poised to take their biggest step yet to make the system more environmentally healthy.

At their weekly meeting tonight, commissioners will receive a recommendation that the city convert its fleet of public transit buses over to a system that largely relies on biodiesel fuel made from soybeans and other plant and animal material.

“I think it is a really exciting time for our bus system,” said Casey Toomay, the city’s interim director of public transit. “We very well may be moving into a new era.”

The recommendation — which came from a study group made up of city and Kansas University transit leaders — calls for the city to purchase four heavy-duty transit buses that are equipped to run on a fuel mixture of 80 percent conventional diesel and 20 percent biodiesel. The buses are expected to cost $350,000 to $370,000 apiece.

The group also recommends the city purchase two hybrid electric buses that would run on a mixture of conventional diesel, biodiesel and electric battery power.

The hybrid buses are expected to cost about $580,000 apiece, or about $200,000 more than traditional buses.

“The hybrids are a test for us,” Toomay said. “It is a recognition that while we have some resources to pay for new buses, the resources aren’t unlimited. The hybrids definitely have a higher upfront cost.”

The study group also examined converting the city’s fleet over to a system that uses compressed natural gas, which has been touted as one of the more effective ways for transit systems to reduce greenhouse gas emissions. But the study group is urging the city to steer clear of that system.

The group said it was concerned it would cost the city from $500,000 to $1 million to build a new compressed natural gas fueling station for the buses. The group’s research also suggested that fuel mileage for compressed natural gas buses would be significantly less.

City Commissioner Mike Dever had urged the city to examine using compressed natural gas buses — which are used at the Kansas City International Airport. Dever said Monday that he was surprised that the buses didn’t measure up better, but said he likely would accept the group’s recommendation.

“This is still going to make a huge impact on our emissions,” Dever said.

The new biodiesel buses are expected to reduce carbon monoxide emissions by about 11 percent and emissions of unburned hydrocarbons by about 21 percent, according to data from the U.S. Department of Energy.

The hybrid buses likely would produce greater declines in emissions, Toomay said.

The city also is holding out hope that it will be able to increase the percentage of biodiesel it uses in the future. Currently, the warranties for new buses don’t allow for more than a 20 percent mixture of biodiesel. But Toomay said that as more research is done, many experts believe higher percentages of biodiesel use will be deemed safe for existing engines.

The city has received $1.9 million in federal stimulus money to help pay for the buses. The city also received $2.8 million in previous federal grants to replace the city’s bus fleet, which is about nine years old. The city will be required to match the federal grants with about $500,000 in local money. The city already has that money set aside from past budget years.

Commissioners meet at 6:35 p.m. today at City Hall, Sixth and Massachusetts streets.