MILAN — The boards of Fiat Chrysler Automobiles and PSA Peugeot on Dec. 18 signed a binding merger deal creating the world’s fourth-largest automaker with the scale to confront the challenges of stricter emissions regulations and the transition to new driving technologies.

MILAN — Italian-American carmaker Fiat Chrysler Automobiles on Oct. 30 confirmed that it is in talks with French rival PSA Peugeot, its second bid this year to reshape the global auto industry, which is facing huge challenges with the transition to electric and autonomous vehicles.