The protesters sat in the road, shouting "No justice, no peace" as traffic continued to back up for miles. At 6:40 a.m., about 20 minutes after protesters walked into the road, police arrested Sharpton and placed him a police van. Then they began arresting others, carrying many from the interstate to waiting police buses.
The highway was reopended shortly after 7 a.m., reports CBS station KMOV-TV in St. Louis.
The protesters want the state to hire more minority contractors for highway construction projects and say talks with Gov. Mel Carnahan's staff over the past week have gone nowhere.
"We can't take it any more. We want our fair share," said Cleo Willis, a welder who sat down in the middle of the highway as traffic backed up and some cars tried to turn around on the interstate.
Members of MO-KAN, a group representing minority contractors, had threatened for about a week to blockade the interstate to draw attention to the group's request that more minority workers and contractors be hired to repair and build Missouri roads.
"How dare they build a highway down the middle of north St. Louis and have no minority contractors," said Marcus Hindmon, MO-KAN president.
The group hoped to mobilize about 10,000 people to close the road.
About 6 a.m., Sharpton, a New York City civil rights activist, joined the crowd, telling those gathered to stand with dignity and not to let anyone provoke them.
"I think that the outpouring of hundreds of people shows this is a serious issue," Sharpton told the group. "This is a very serious matter that cannot be ignored."
Sharpton, who arrived in St. Louis on Sunday, said "unfairness and equity" had brought him to the city.
Despite talks last week between government officials and MO-KAN, protest organizers said Sunday they would go through with plans to barricade the region's busiest interstate. Some construction crews were planning to take the day off.
A spokesman for Gov. Mel Carnahan said negotiations continued late Sunday night.
The employment dispute centers on a request from MO-KAN calling for minorities to make up 35 percent of workers and 25 percent of contractors in construction projects.
Several highway projects, including bridge and overpass reconstruction, are being done this summer throughout St. Louis. Some of these projects border urban neighborhoods.
State transportation officials say their quotas are fine by national standards.
Missouri authorities claim the state surpasses the federal requirement of hiring 10 percent minority contractors. They say their hands are tied since contracts for current projects have already been awarded.