The often on again-off again Keystone XL Pipeline project has been touchstone of environment activism for about 13 years, but now it appears it is off for good.

Last week, TC Energy, the Canadian company behind the pipeline, said that it had decided along with the government of Alberta to end the multibillion-dollar project. XL was the focus of frequent delays, construction permit battles, and changing government policies. It was the bane of environmentalists because of its scope and because tar sands are among the filthiest, most polluting form of fossil fuel. If completed, the 1,200-mile pipeline would have carried 830,000 gallons of oil from the vast tar sands mines in Alberta to refineries on the US Gulf Coast.

A Sierra Club article on the pipeline termination said: “The whole operation would have added more than 181 million tons of carbon-dioxide-equivalent greenhouse gas emissions to the atmosphere each year. Oil from the tar sands is some of the dirtiest on the planet, producing 20 percent more CO2 than conventional crude. Along the way, the Keystone XL Pipeline would have passed through Montana, South Dakota, and Nebraska, where it would have threatened farmland, drinking water, and wildlife habitat.”

Keystone is gone but the writing is on the wall for other pending projects, so stay tuned.