Seal coating, an annual Minneapolis Department of Public Works maintenance project, created the dusty conditions on Hennepin Avenue last week that caused cars to slow and bicyclists to wipe their eyes.
Hennepin Avenue underwent the process, meant to extend the life of pavement, from July 28th through the 31st, said Mike Kennedy, director of transportation, maintenance and repair for Public Works. Although traffic was never completely closed, lanes were reduced and no parking was enforced.
Although the project is always dusty, this year was remarkably more so, and they aren’t sure why, Kennedy said. It could be that they simply received a dusty portion from the vendor’s rock chip pile, he said. It could be Hennepin’s heavy traffic load; in which case the many trucks and buses going by would have ground the gravel up more than usual and sent dust into the air.
“We’ve been looking at our processes and haven’t found the smoking gun here, so to speak,” Kennedy said, adding that the department will adjust their processes in the future.
When the dust became problematic, the crew re-swept the area to remove excess dust and applied water to seal in the chips throughout the weekend. By now, Kennedy said, the problem seems to have dissipated, although maintenance will respond if the situation changes. Other Minneapolis streets and metropolitan areas received the same treatment this year with no dust issues.
Seal coating begins with prepping the street. Then, a coat of liquid asphalt is laid, followed by a layer of rock chips, varying from pea-sized to dust-sized particles. The chips are rolled into the asphalt, which adheres them into the pavement. Traffic is then re-opened over the area to help work the rocks in. Three to four days later, the crew returns to sweep the excess chips, a process called reclaiming. The extra chips are recycled for use in future projects.
The city’s seal coating program has lost significant funding over the past couple of years. The program, which used to receive about $3 million in its more aggressive era, now operates at about $1 million, Kennedy said. While it’s a very cost-effective and popular thing to do in urban areas, there simply isn’t a lot of money in the budget for it anymore.