From Alligator Cracks to Potholes: Street Repair 101

It’s no small task to maintain the 150 miles of road in Inver Grove Heights.

Already this year, the city plans to undertake an extensive street reconstruction project in the South Grove neighborhood of Inver Grove Heights, which will likely include the complete reconstruction of portions of Dawn Avenue East, 69^th Street E., Craig Avenue E. Crosby Avenue E. and several other streets.

While the South Grove project is likely the largest street project the city will undertake in 2011, it’s hardly the last. The city and the council will begin identifying other priority street projects later this spring, Public Works Director Scott Thureen said.

With such an extensive road network, how does the city monitor the state of its roads and identify sections of street for repair?

The answer lies in a complex pavement management system the city implemented in 2001.

Each year, the city hires consultants to inspect one-third of its total road mileage — or roughly 50 miles of streets. When the inspectors are examining a road, Thureen said, they look for various types of cracking or “distress” in the road surface. Each type of distress found is like the symptom of a disease — it can be used to evaluate the general health of the road and, in some cases, the condition of the road base beneath the pavement, Thureen said.

Symptoms of a road in need of repair include: Latitudinal cracking, or cracks that stretch across the width of the road. Latitudinal or transverse cracking is usually one of the first symptoms of a deteriorating road to appear, and is usually followed by longitudinal cracking, or cracks that stretch lengthwise down a street. Longitudinal cracks frequently follow the midline of a road, and can easily form deep ruts.

When several latitudinal and longitudinal cracks intersect, they can form a “block,” or a square in the pavement, Thureen said. Block cracking can be a precursor to the more severe “alligator cracking.”

Named for the rough skin of an alligator, alligator cracking is a concentrated spiderweb of cracks. Its appearance can be an indicator of poor road and subsurface conditions, Thureen said. Alligator cracks can form potholes — the suspension-rattling bane of motorists.

Inspectors also look at whether a road is suffering from “settling” — a condition that occurs when heavy traffic causes portions of a road to sink, forming tire ruts. Crews also run cameras through storm and sanitary sewer pipes beneath the roads to evaluate pipe conditions.

Once an inspection is complete, the inspector’s observations are entered into a software system, which automatically rates the road segment on a 0-100 scale, Thureen said.

A rating of 100-66 is considered adequate, and roads in this category may be eligible for crack sealing and seal coating treatment. Roads with a score between 65 and 36 are candidates for a mill and overlay — a process by which crews strip the top layer of pavement from a road and repave the surface. Roads in the worst category, with a rating of 35 and below, are targeting for a complete reconstruction, Thureen said.

Roughly 90 miles of city road are in the “adequate” category, Thureen said, while an additional 30 miles of road in Inver Grove Heights has a rating of 35 or below. Typically, the city will mill and overlay a road 20 years after its original construction. A reconstruction takes place between 50-60 years of the original construction, Thureen said.

For more information about Inver Grove Heights road projects, click here.