LOUISVILLE, Ky. — Long ago, the Ohio River helped make this Rust Belt city a national pacesetter in manufacturing and transportation, providing it with an identity and an anchor. But as American life shifted toward the automobile, the river also became an impediment.

Now, after decades of planning, the city intends to begin construction on a $2.6 billion two-bridge project that is said to be the costliest in the state’s history.

Along the way, planners of the Ohio River Bridges Project scaled it back by $1.5 billion to make it financially palatable and had to clear a series of obstacles raised by residents and activists on both sides of the river. The opponents often quarreled among themselves as much as with elected officials.

Although friction about some aspects of the project still reverberates, including over its tolls and environmental impact, construction is scheduled to begin this summer, and the two new bridges linking Kentucky and southern Indiana are expected to open in 2016. One bridge will be in downtown Louisville, and the other will serve an area just east of downtown.