MoDOT inspectors “snoop” under bridges to check condition of structures
An under bridge inspection unit, also known as a snooper truck, is an odd looking vehicle that causes many who see it to do a bit of a double take. On May 27, there were many spectators at Table Rock Lake in Branson, that did just that. While they were watching from the lake front, dam observatory and occasionally from idling boats, a four-man MoDOT crew was assisting the Army Corps of Engineers in the inspection of the dam.
The under bridge inspection unit on location in Branson that day is one of only three in the state. With so few units statewide, each truck and crew covers a large portion of Missouri and its bridges. All three crews are part of the Bridge Management Section of the Bridge Division.
The trucks and the crews that operate them are an invaluable asset when it comes to making sure the bridges of Missouri are safe for motorists. Every bridge in Missouri is inspected regularly for safety. If a disaster happens, a bridge must be inspected immediately before motorists will be allowed to drive on it for their safety.
In order for the crew to inspect under the bridge, the snooper truck can extend its arm allowing the operator to go off the side of the bridge. A counter weight on the truck prevents the unit from tipping over. The arm is then maneuvered into position underneath the bridge for inspection. The truck’s arm can lower itself and reach a total of 62 feet across the width of a bridge for the inspector to check for cracks, damage and deterioration.
If a crack is found, it is measured and evaluated to make sure it is not compromising the integrity of the bridge. Not all cracks are equal. While bridges will have cracks, the crew is looking for cracks in areas of stress, or cracks that show growth from a previous inspection. They also are testing the thickness of the steel in areas of section loss caused by rust to make sure it is still in good condition.
According to the bridge inspection crew, it is not uncommon to close up to two bridges a month in need of immediate repairs. The bridge deterioration can be caused by numerous things. It can be from the salt and abrasives added during winter to help keep ice off the bridges that cannot be reached to wash away, or simply from fatigue over time caused by heavy trucks passing over it.
In Missouri, there are more than 10,400 state bridges. A total of 208 bridges are considered “major” meaning they exceed 1,000 feet in length. Currently 47 of those major bridges are considered to be in poor condition while an additional 97 are only considered to be in fair condition. Overall a total of 6,598 bridges are in fair to poor condition.