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After more than a century and 20 million autos built, the General Motors Co. plant in Oshawa, Ontario, will make its last vehicle Dec. 18 when a final pickup truck rolls off the line.

Oshawa’s car-making roots go back to 1867, the year of Canada’s Confederation, and the founding of a carriage company by the McLaughlin family. GM has been producing vehicles at the plant since 1918, making it the company’s oldest existing assembly plant.

The business survived two world wars and the Great Depression and grew into one of the world’s largest auto manufacturing facilities with tens of thousands of employees. It even survived GM’s 2009 bankruptcy. But the Oshawa assembly plant could not weather two other inexorable forces: the emergence of low-wage Mexico as an automaking powerhouse and GM’s bet on electric vehicles.

The shutdown of Oshawa assembly is part of a reorganization by GM to trim excess production as industry sales soften and shift resources to electric and autonomous vehicles. The overhaul cut a net 11,000 workers across the company. The Oshawa plant had been making Chevrolet Silverado and GMC Sierra pickups.

Starting next year, the site will be used for parts manufacturing and a test track for advanced technology vehicles. Of the roughly 2,200 employees GM says are affected, 1,600 are taking buyout packages, including 1,200 who will retire on defined benefit pensions, giving them a guaranteed income for life.

About 300 employees will be able to work at the new operations and about 100 have transferred to GM facilities elsewhere in Ontario. Two hundred are hoping to be recalled, either in Oshawa or elsewhere in Ontario, and will receive layoff benefits in the meantime, according to Jennifer Wright, a GM Canada spokeswoman.

A group of workers is lobbying the government to take over the plant and convert it to electric-vehicle production. The employment losses rise to about 5,000 when hundreds of temporary part-time workers are taken into account, along with over 1,000 outsourced GM jobs and more than 1,000 supplier jobs, according to Tony Leah, a spokesman for Green Jobs Oshawa and chairman of the political action committee for Unifor Local 222.

For its part, GM says the creation of an autonomous testing track, named after Col. Sam McLaughlin, will continue the company’s legacy in Oshawa. The automaker is also boosting its headcount of software engineers in Markham, Ontario, about 30 miles to the west of Oshawa.

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