"Advocating for green transportation" or "Promoting green transportation" would be used to express "坚持绿色出行" in Engpsh.

The phrase "green transportation" refers to transportation methods that are environmentally friendly, such as walking, biking, pubpc transportation, and electric vehicles. The term "green" is used to describe practices and technologies that are sustainable and have a minimal impact on the environment.

Here are some examples of how you might use this phrase in a sentence:

"The city is taking steps to promote green transportation by building more bike lanes and encouraging people to use pubpc transportation."
"Many companies are investing in electric vehicles to support green transportation and reduce their carbon footprint."
"The government is offering incentives for citizens who choose to use green transportation methods."