The City & County of San Francisco has ended its use of petroleum diesel and completed the switch to renewable diesel for the city fleet. The change is estimated to reduce fleet diesel greenhouse gas emissions by 50%.

Mayor Edwin Lee made the announcement Dec. 11, nearly five months after first announcing that the city would begin using renewable diesel.

“As the global climate negotiations conclude, San Francisco and cities worldwide must continue to lead by taking bold actions that reduce greenhouse gas emissions immediately,” said Mayor Lee in a release. “These actions cannot wait.”

San Francisco completed the switch to renewable diesel at all of the city’s 53 fueling sites. This change affects 1,966 vehicles that rely on diesel fuel. City Administrator Naomi Kelly said the use of biodiesel is cost-neutral to the city due to state and federal incentives to use the fuel.

In fiscal-year 2014, the city used 5.8 million gallons of diesel fuel, of which 4.9 million was petroleum diesel, resulting in the emission of approximately 100,000 metric tons of greenhouse gases into the atmosphere. The City’s Fleet Management Division estimates a 50% reduction, or 50,000 metric tons, in greenhouse gas emission as a result of ending replacing diesel with renewable diesel.

The city chose to transition to renewable diesel after a successful pilot led by the Fire Department. The city had previously been using B-20 biodiesel for most of its municipal fleet.

Renewable diesel and biodiesel are both produced from bio-feedstock sources, including fats, oils and greases, but the two fuels are produced through different processes. Renewable diesel uses a hydrogenation process, while biodiesel uses an esterification process. According to the California Air Resources Board, the full lifecycle emissions of carbon from renewable diesel produced from sustainable sources are more than 60% lower than either petroleum or B-20 biodiesel. Chemically, renewable diesel is indistinguishable from petroleum diesel, and testing has shown it to have engine performance that matches or outperforms both petroleum diesel and biodiesel, according to the city.