If Bridges Could Talk

There are more than 600,000 bridges in the U.S. alone and one in three of those bridges have identified repair needs.i Bridges are important as they stand between you, where you are and where you want to go. More than 25% of the U.S.’s bridges were built between 1957 and 1971.ii These years represent the “baby boom” for bridges and reflect increase in bridge construction during the development of the interstate freeway network. Consequently, the average age for a highway bridge in the U.S. is 43 years,iii just about the right amount of time for a midlife crisis. Therefore, these older bridges will require major rehabilitation in the next decade.iv

Our world’s bridges represent precious assets that need careful attention, especially as they move into old age. Just like people, our bridges are expected to carry a lighter burden as they get older and in fact, many of our older bridges have a traffic weight restriction imposed to manage further deterioration. To ensure that they live past their design life, let’s listen to what our bridge and traffic data is telling us and follow through in providing the necessary support required.


One of the important areas in bridge preservation lies in the enforcement of proper usage. While bridge preservation also includes protection from further structural deterioration, structural maintenance, and inspection, proper usage of the bridge also plays an important role in preservation.

Bridges are designed for certain types of traffic, characterized by the size, weight, and height of the vehicles. For the bridge to be used properly, traffic must comply with the design characteristics. Is it too late to monitor the characteristics of traffic intending to use the bridge if the vehicles have already approached the bridge? Monitoring before the last decision point on the traffic route should be required. In other words, noncompliant traffic should have an alternative route available, in advance of the bridge.

This type of advance monitoring can be combined with in-vehicle information and roadside dynamic message signs to provide guidance and advice to vehicle drivers on an alternative route that would avoid the bridge. This is particularly important with respect to overloaded trucks, which have the potential to cause major damage to the bridge. Using International Road Dynamics (IRD) Inc.’s Weigh-in-Motion (WIM) technology, such trucks can be identified and managed well in advance of the bridge.

IRD can supply complete systems that:

  • Identify overweight vehicles
  • Capture images of overweight vehicles
  • Identify vehicles with automated license plate recognition
  • Check the dimensions of vehicles and compare vehicle data with safety databases that may have prior data regarding the vehicle
  • Automatically divert vehicles using message signs

Another way to preserve bridges lies in determining a detailed understanding of the weight of traffic using the bridge and how the bridge responds. The same WIM technology used to weed out overloaded trucks can also be used to provide viable data to estimate the operational life of the bridge. Sensors can be placed on bridge approaches to provide data on the loading being experienced by the bridge. These include variations in loading and traffic flow over time and an estimate of road damage based on loading. Automated approaches to the collection of bridge data like this, enable long-term assessments to be supported that reveal insight into changes in the performance of the bridge and the expected volume of traffic to be carried over time. Longer-term methods can also take account of changes in truck geometry, axle configuration, suspension, and tire characteristics as truck design advances.

The Bigger Picture

IRD sensors can also be used to take a network-wide view of truck traffic. This provides the ability to optimize truck flows, to accommodate bridge performance, and to manage truck traffic on a network-wide basis. Therefore, bridge management should be embedded into an overall transportation management plan for the entire network for both routine and non-routine event conditions.

Senior Bridges

It seems to me that we must pay a lot more attention to all our bridges but especially our older bridges here in North America. Many of our bridges have names, the George Washington Bridge comes to mind. Maybe it is time to give bridges memorable names to indicate their importance and provide the necessary level of resources and attention to those classified as structurally deficient. Next time you drive over your local bridge, consider the service that it has provided for you in the past, is providing for you in your current trip and will provide for you in the future. Give a thought to the name that you would give to your bridge, based on your perception of its characteristics, and consider what you can do to help it in its old age.

I have started to think about what I can do to pay back all the service that my local bridges have delivered over the years. Maybe, I can bring the cause to public attention and then provide cost-effective solutions for understanding how to rehabilitate structurally deficient bridges across the country. I also wonder if bridges could talk, what would they say? Ouch!

[i] https://www.artba.org/2018/01/29/54000-american-bridges-structurally-deficient-analysis-new-federal-data-shows/


[iii] https://www.infrastructurereportcard.org/wp-content/uploads/2017/01/Bridges-Final.pdf

[iv] http://www.comt.ca/english/NHS-Condition09.pdf

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