Bridge Safety Since the Minneapolis I-35W Bridge Collapse:
Since the collapse of the I-35W bridge in Minneapolis on August 1, 2007, there has a great deal of attention given to the safety of local bridges. And for good reason…about two-thirds of all bridges in Ohio are maintained by County Engineers.
News reports following the bridge collapse in Minnesota showed that about 25% of Ohio bridges are either structurally deficient or functionally obsolete. Many people were alarmed at this statistic and immediately began asking questions about how safe the bridges they cross every day really are. After all, the terms “structurally deficient” and “functionally obsolete” can make the average motorist feel a bit uneasy.
Motorists should rest assured knowing that there are thousands of bridge engineers and inspectors working every day to ensure the safety of Ohio bridges. Collapses are extremely rare because of the extensive bridge inspection and inventory procedures that are required by law. While a bridge may be considered “structurally deficient”, people should be aware that this does not mean the bridge is unsafe. It does mean that there are issues with the bridge that require attention. These may be things such as structural elements that don’t carry as much weight as they were originally designed for, but are still sturdy enough to safely carry traffic. Other deficiencies such as the bridge being too narrow to meet modern road safety standards will classify a bridge as deficient.
The Delaware County Engineer takes very seriously his responsibility to ensure the safety of the traveling public. Any bridge that is not safe to cross is closed and/or repaired. Remember that the bridge engineers that inspect the Delaware County’s bridges drive across these same bridges with their own families.
Condition of Delaware County Bridges:
The Delaware County Engineer inspects 378 bridges in Delaware County. A bridge is considered any structure over or under a County or Township roadway that is 10 feet in span length or greater, measured along the center of the road. Examples of these structures are steel beam bridges, concrete bridges, steel truss bridges as well as large diameter circular culverts and long span box culverts.
Since 1998, over 200 county bridges have been built or rehabilitated. This represents over half of the entire bridge inventory.
Bridge Load Carrying Capacity:
By design, bridges are built to carry the loads caused by heavy trucks throughout the life of the bridge. However, many bridges that were designed and built long ago were not designed for the heavier trucks that travel the roads today. This affects the traveling public in several ways.
First, for bridges that cannot safely carry Ohio Legal Loads, the County Engineer is obligated to post signs indicating the maximum safe load that the bridge can carry. Posted bridges have signs placed near both ends of the bridge and at the nearest approaching intersection, warning all motorists that the bridge is not capable of safely carrying the maximum Ohio Legal Loads. For passenger cars and light trucks, this is generally not a concern since most cars and light trucks do not exceed 3 or 4 tons in weight. But for heavier trucks, such as garbage trucks, delivery trucks or fuel trucks, a bridge that is posted at 10 tons, for instance, cannot safely support the heavy load of that truck.
Secondly, for special loads that exceed the limits established by Ohio Law, such as transporting heavy construction equipment, permits are issued to regulate overweight loads. The County Engineer’s Permit Department issues permits that allow overweight vehicles to legally and safely use County and Township roads. In order to route vehicles so that they do not cross weaker bridges that can’t support their weight, the Design Department updates the Bridge Load Rating Map on an annual basis. This map can be used by trucking companies, crane companies, and other companies that need to haul overweight loads across County or Township roads to determine which route they must take to avoid weaker bridges.
Ohio Legal Loads:
Section 5577 of the Ohio Revised Code (ORC) sets forth the maximum allowable loads on Ohio roadways. No vehicle can legally exceed a total gross weight of 80,000 lb., regardless of the number of tires or axles. In order to legally weight 80,000 lb, the trucks must be long enough to distribute the load across the highway pavements and bridges. These are the longer trucks such as the typical tractor-trailer trucks or tanker trucks seen on the interstates. For shorter vehicles with only a 10-foot wheelbase, the maximum allowable load is 40,000 lb., as long as tire size requirements are met. Vehicles such as delivery trucks and garbage trucks generally fall between 40,000 and 80,000 lb. legal limits.
The County Engineer determines which bridges require replacement or corrective action by physically inspecting them on a regular basis. According to ORC section 5543.20, the County Engineer must annually inspect all bridges 10 feet or greater in span length on every county and township road to assure the safety of these bridges. At the end of each year, the County Engineer reports the condition of each inventory bridge to the Ohio Department of Transportation. ODOT maintains a master inventory of every bridge in the State, and also inspects all bridges on State and Federal routes annually.
Bridge inspectors are engineers or technicians that are experienced in the design and evaluation of bridges. To become an ODOT qualified inspector, County staff engineers attend a six-day training course where they receive hands-on training about how to properly inspect bridges and culverts. This training, combined with college engineering education and years of experience ensures that the inspection of bridges is properly done to protect the safety of the traveling public.
Bridge Maintenance and Replacement Program:
Through annual inspection of county bridges, the County Engineer can plan and program the repair and/or replacement projects for those structures that are found to be deficient. Even with regular maintenance, bridges eventually deteriorate to the point that they are no longer serviceable, either because of structural deficiencies that limit their load carrying capacity or because they are no longer functionally adequate for the road in which they serve.
Bridge Program Since 1998:
Since 1998, the County Engineer’s Office has made great progress in replacing, rehabilitating or repairing deficient bridges. In 1998, nearly 38% of the county’s bridge inventory was considered deficient (either structurally deficient or functionally obsolete). 20 years later, over 200 bridges have been rebuilt or replaced, and only 4% of the inventory remains deficient.