Like many states, South Carolina faces challenges in maintaining its highway system due to the declining purchasing power of state and federal gas taxes, the rising maintenance needs of an aging highway network and the increasing costs of construction materials. South Carolina is looking for any method to reduce its roadway maintenance costs.
The South Carolina Department of Transportation (SCDOT) has embraced an innovative bridge monitoring system that uses Advanced Condition Assessment Technology (ACAT) to supplement or replace certain bridge inspections as one way to reduce expenses. The bridge monitoring system uses sensors installed on specific bridges to track bridge performance. The sensors enable bridge life to be extended on structures that would otherwise need to be replaced. While adaptation of the technology has proceeded slowly, the latest surface transportation bill—Moving Ahead for Progress in the 21st Century (MAP-21)—that requires asset management plans could increase the popularity of this technology. Since these sensors monitor bridge conditions, many states could include them as part of their federally mandated asset management plans. Other factors including limited budgets and litigation may encourage states to adopt the technology.
Reason Foundation Assistant Director of Transportation Policy Baruch Feigenbaum recently interviewed SCDOT State Bridge Maintenance Engineer Richard “Lee” Floyd to discuss the technology behind ACAT bridge monitoring, its expansion, and other advantages to the technology.
Baruch Feigenbaum, Reason Foundation: Bridge replacement can be a costly, complicated affair. SCDOT’s ACAT system can extend the life of bridges. How exactly does it work?
Richard "Lee" Floyd, State Bridge Maintenance Engineer, South Carolina Department of Transportation: The bridge monitoring system from LifeSpan Technologies uses girder sensors placed on certain bridges to measure the carrying capacity of the facility. (Other companies that offer similar technologies are Advitam, Bridge Diagnostics, Inc., Canary Systems, Chandler Monitoring, GeoComp, Olson Engineering and Instruments, and Smart-Structures.) Each bridge has two sensors. The sensors relay information wirelessly to computers in our office that we can monitor 24 hours a day, seven days a week.
The system has several other advantages: it can operate on batteries so it does not require power to operate, it limits the number of interim inspections since the bridge sensors provide regular feedback, and it allows continuous monitoring of bridges.
The sensors work with our traditional human inspection system. The system does not take the place of physical inspections. One issue we found with physical inspections is that these inspections seem to underestimate the strength of the bridge. We found that we were replacing bridges that had up to five more years of life. The bridge monitoring provides a more realistic view of the bridge life and provides real time information on the weight the bridge can handle.
In South Carolina, we have several fracture-critical bridges that we would like to replace immediately. Unfortunately, we do not have the resources. The bridge sensors allow us to safely extend the life of the bridge and allow us to spend limited resources on other critical needs.
These sensors benefit different bridges in several ways. They might allow us to eliminate weight restrictions on one bridge, keep a bridge open that we otherwise would have closed, or increase the amount of time before we replace a bridge.
Feigenbaum: Could this replace traditional bridge inspections?
Floyd: At this time, we feel more comfortable with the system as a supplement. We do not envision the system taking the place of bridge inspectors.
Feigenbaum: What are the cost savings of the system?
Floyd: The cost savings are substantial. We were able to retrofit one of our fracture-critical bridges for $100,000 versus spending $800,000 for a new bridge. That is $700,000 in savings for just one bridge. We have bridge sensors on eight of our facilities and are looking to add sensors to several more. Even with just eight bridges, we are talking about a savings of approximately $5 million. We have more than 8,000 bridges in the state. If we use these sensors on just 1% of all bridges, we are talking about a savings of $56 million.
Feigenbaum: Does bridge monitoring have benefits beyond determining structural integrity?
Floyd: Yes. There are several other benefits. We use bridge sensors to monitor a coastal bridge in Charleston. If wind speeds get too high (from a hurricane for example) we would close that bridge. The sensors provide a low-cost alternative to dedicating an employee to monitor the bridge on-site or relying on nearby wind readings that might be inaccurate.
Bridge monitoring has also allowed us to catch overweight trucks crossing a bridge with a weight restriction. We have three portable sensors that we can move from bridge to bridge. I typically check the sources twice a day. One night around midnight I noticed that the sensors indicated the bridge was under a lot of strain. We sent law enforcement out to investigate and discovered that logging trucks that were over the posted weight limit were using the bridge at night. We ticketed some of those drivers, who are probably still wondering how we knew that they were overweight. Overweight vehicles can wear bridges 10 times faster than cars and damage older bridges, so it is important that they do not use these bridges.
Feigenbaum: How many bridge monitors do you have?
Floyd: We have three portable units that we can move around and two permanent units for a total of 18–20 sensors. For the portable units, we can set the thresholds electronically and remotely over the Internet as we move them from bridge to bridge.
Feigenbaum: How much time can these sensors buy?
Floyd: We can delay replacing most of our bridges by three to five years. With a limited budget this is a huge benefit.
Feigenbaum: SCDOT was one of the first DOTs to use this technology. Are other states beginning to make use of it? Are there reasons some states are not using the technology?
Floyd: We have seen slow but steady growth. Internationally, especially in Europe, this technology is in widespread use. Arizona, Michigan, North Dakota, Pennsylvania and Utah are using the technology. The biggest barrier to implementation is generational. Bridge engineers who have been conducting physical examinations are reluctant to trust technology even when the research studies show that the technology is more accurate and effective. Younger bridge engineers seem to trust the technology much more than older bridge engineers.
After a slow start, the Federal Highway Administration is beginning to encourage its use. We are trying to get a $1 million FHWA grant to expand the system to other bridges. We applied for a grant in the TIGER III and TIGER IV grants and were turned down by USDOT despite the fact that the grant was a cost-effective solution to a major problem.
Feigenbaum: Is the new software challenging to use? Do state DOTs need specific training?
Floyd: LifeSpan and some of the other companies offer a one and a half hour training course so staff understands how to use the system. The course teaches staff how to use the power sensors, how to apply the sensors to steel and concrete, how to handle the sensors properly, how to get the data, and how to reset the sensors. These tasks are not all that challenging but if you are paying for the system you want to understand how to use it. Proper usage will also maintain system life.
Feigenbaum: Are there other types of infrastructure that could use this technology?
Floyd: Railroad owners could see major benefits as well. Most railroads have bridges in remote areas; some do not see much traffic. A monitoring system would notify the dispatcher if something came down on the track or if weather conditions (high winds for example) prevented safe operation of a train.
Richard “Lee” Floyd is South Carolina Department of Transportation’s State Bridge Maintenance Engineer. Floyd advises other engineers on best practices for bridge management.
Other articles in Reason Foundation's Innovators in Action 2014 series are available online here.