Nobles County facing bridge woes
WORTHINGTON -- Increased truck traffic and vehicles designed to carry larger loads are creating a toll on Nobles County's bridges that were designed 30, 50 and up to 70 years ago.
That toll is showing as new weight restrictions will be placed on nine bridges in the county this month. Another bridge, located south of Brewster, has a width restriction after a partial failure in October led to a milling machine plunging toward the creek below. That bridge has since reopened to one-lane travel.
Nobles County Public Works Director Stephen Schnieder said most of the bridges to be posted for weight limits are due to a new vehicle on our rural roads -- a short length straight truck with multiple axles that can be on the bridge span all at one time.
Five bridges on the county's road system had to be restricted because of that new vehicle, and four others will be restricted for all types of truck configurations.
"We have five roads that are affected," said Schnieder, adding that in addition to County State Aid Highway 1 south of Brewster, they are CSAH 14 (one is west of Brewster and the other is south of Lismore); CSAH 19 (one south of Leota and one north of Ellsworth); CSAH 3 (both west of Brewster, one north and one south of Nobles County 14); CSAH 6 (one spanning the Little Rock River and one spanning Norwegian Creek); and one on Nobles County 60, south of Wilmont.
With the new weight restrictions, Schnieder has asked for additional patrol, particularly on the CSAH 14 bridge west of Brewster, which has been posted down to 10-ton (20,000 pounds) because wooden pilings that brace the bridge are rotting.
"People need to understand that we post the bridges No. 1 for safety so we don't have a gross failure," said Schnieder. "Most often we don't see a section of the bridge fall into a creek like we did on County Road 1 south of Brewster. What we see are sections cracking or starting to fail."
Inspections and deterioration
The bridges were identified for restrictions after a consultant hired through the Minnesota Department of Transportation conducted ratings and inspections on them this summer.
With 345 bridges in Nobles County -- 209 on township roads and 136 on county roads -- inspections are typically conducted on a two-year cycle unless a bridge is showing some deterioration, in which case an annual inspection is necessary. Schnieder said a bridge can be anything from the old timber structures to precast concrete culverts or a series of culverts, as long as its span is more than 10 feet or has an opening underneath the road.
The 10 new additions to the county's list of restricted bridges are all timber bridges, which are commonly found on the eastern side of the county. Two of them were built in the 1950s; six in the 1960s; and two in the 1970s.
"Generally, we expect the bridges to last 75 to 80 years, but we're seeing these aren't making that design life," Schnieder said. "These bridges designed 50 years ago were designed for a different vehicle. As we increase the weight loads for trucks and wagons, the bridges weren't designed for that weight. We may run into the same problem 50 years from now."
These days, Nobles County tries to replace timber bridges with precast concrete box culverts whenever possible.
"Boxes are anticipated to last longer than a bridge, they require less maintenance and there's unrestricted width for getting wider loads across the structure," Schnieder said.
Design costs for precast concrete culverts are also about one-fifth the cost of a new timber bridge and construction can be done in one-tenth the time.
During his report to Nobles County Commissioners on Thursday, Schnieder outlined three bridges he recommended as top priorities for replacement. Those bridges include the CSAH 1 bridge that is reduced to one-lane travel; the CSAH 14 bridge west of Brewster that has been posted down to a 10-ton weight limit; and the CSAH 14 bridge southeast of Lismore. All three bridges are located on primary routes to Brewster, home of Minnesota Soybean Processors.
After the one-lane bridge south of Brewster, the CSAH 14 bridge west of Brewster is considered to be in the worst condition with its rotting timber pilings. The timber that is exposed to wave action, going through wet and dry periods, deteriorates the fastest.
Though the bridge is still safe for lighter loads to travel across it, Schnieder said it's those heavier trucks that can cause a quick deterioration to the structure.
"My fear is they will damage the bridge to the point where the next school bus that goes across it is going to (cause it to collapse)," Schnieder told county board members. He said the overweight trucks aren't kept from crossing the bridge, the safest thing to do would be to close it.
Once county commissioners prioritize the bridges, an application will be made for state bonding money. At this time, though, there is little to no money available for bridge replacement, Schnieder said. The best case scenario is that the state legislature will authorize a bill for bridge replacements during the 2011 session.
The board has another option, however, which would be to fund the projects with the county's allotment of state aid money or local property tax dollars. Utilizing those funding streams would take away from other projects in the county's road improvement budget.
Finding the funds
Schnieder said if all 10 of the bridges were to be replaced within the next year, the cost would be in the $3.5 to $4 million range. If funding was used from the state gas tax, Schnieder said the county would be responsible for 50 percent of the cost, which is still in the neighborhood of $1.7 to $2 million.
In recent years, counties have had fewer dollars available to them through the state's gas tax. In Nobles County, Schnieder said revenues have dropped $10,000 to $20,000 in each of the last two years, and he looks for another slight decrease in 2011.
Revenues are down statewide because people are driving less and driving more fuel efficient vehicles. Also, fewer new vehicles are being sold and people are choosing to drive vehicles longer, both of which limit the amount of money collected for license tab fees
As such, the priorities are identified and the remainder of the bridges will be rolled into a five- or even 10-year replacement plan.
"There's a very good potential that you would have other bridges come up in the meantime and have to be added in front of these other bridges we already know about," Schnieder said.