As transportation networks expand and age, ensuring the safety and efficiency of roadways and railways becomes increasingly critical. Traditional monitoring methods often rely on discrete sensors or manual inspections, which can be limited in scope and responsiveness. Enter Distributed Fiber Optic Sensing (DFOS), a transformative technology that leverages existing fiber optic cables to provide continuous, real-time monitoring over long distances.
Distributed Fiber Optic Sensing, or DFOS, is the idea that existing fiber optic cables can be used as sensors. Regular fiber optics are used as the backbone of the global telecommunications network, using light signals sent through a fiber made from silica to send and receive huge amounts of data at nearly the speed of light. Instead, DFOS forgoes data transfer and measures the backscatter of light to take measurements in temperature, strain and vibration. These changes can be pinpointed to specific locations along the fiber, and can have a spatial resolution of over 50 feet. Fiber optic sensors have been implemented in various applications, including pipeline monitoring, earthquake detection, border security, and more.
Distributed fiber optic sensing takes this one step further by utilizing existing single unused dark fibers as sensors. Often fiber optic cables are placed along utility corridors, making them ideal for monitoring utilities and the ground underneath cities. The ability to precisely measure vibrations and minute changes in the environment makes it ideal for measuring transportation infrastructure and protecting public infrastructure.
Utility for Transportation Infrastructure.
DFOS is ideal for monitoring transportation infrastructure because it is already there. Fiber optic infrastructure is the backbone of the internet, stretching for millions of miles across the U.S. Unused dark fiber optic cables can easily be converted into fiber optic sensors, requiring almost no new infrastructure investment. These fiber optic cables are located in utility corridors that travel underneath streets and across rail tracks.
DFOS can provide continuous monitoring of roads, detecting ground movements, changes in temperature, and measuring structural health. Although challenging, new algorithms are capable of taking traffic and structural data to detect road anomalies, improving maintenance data and public safety. Fiber optic cables in bridges can provide structural health assessments, which have been shown to reduce overall lifetime costs for bridges by 10%.
DFOS has also been shown to be capable of traffic monitoring and management. While the technology is still under development and algorithms are refined for increased accuracy, significant progress has been made in recent years. Existing fiber optic cables have been used to measure traffic and human activity in social studies, measuring significantly decreased activity during COVID-19. This measurement of vibrations also extends to earthquake monitoring, which can provide data to early warning systems to protect people and infrastructure at risk
Railroads can also benefit from fiber optic sensing. DFOS may be located nearby rail lines, particularly in more urban environments, providing valuable data for track monitoring, train movements, and hazard monitoring. However, the largest benefits from the technology to rail lines likely come from dedicated fiber optic sensors, which are extremely effective at detailed track measurements and provide significantly more data than traditional point sensors. Fiber optics allow continuous and comprehensive monitoring for physical intrusion security, hazard warning, and track condition. Traditional monitoring technologies cannot measure the entire length of a track effectively like fiber optic sensors, and provide less data for maintenance workers correcting track defects.
Challenges and Considerations
DFOS represents a fantastic opportunity to utilize existing infrastructure to expand data collection and improve safety for transportation infrastructure. Other than the small computer, called an interrogator, attached to one end, fiber optic sensors require no electricity and minimal upkeep. However, there are some limitations to distributed fiber.
The biggest strength of DFOS is that it is already installed and requires far fewer investment than other sensor systems or infrastructure solutions. However, this benefit only extends as the existing fiber does itself. Many places do not have underground fiber to measure road or rail track conditions. Installing dedicated fiber optic sensors can also bring enormous benefit, and has been demonstrated for both traffic monitoring and protecting rail lines, but it does not have the same cost-benefits as DFOS.
Additionally, DFOS is still a technology under development. There are limitations on using distributed fiber for traffic monitoring. Increasingly advanced algorithms and AI are improving processing and classification data, but the technology is at the cutting edge of progress.
Distributed Fiber Optic Sensing presents a significant advancement in the monitoring and protection of road and rail infrastructure. The ability to provide continuous, real-time data enhances safety, optimizes maintenance, and extends the lifespan of critical transportation assets. As the nation works to modernize aging infrastructure while expanding new systems, integrating DFOS into infrastructure management strategies will be essential for building resilient and efficient transportation networks.
Written by Owen Rogers, Public Policy Associate
The Alliance for Innovation and Infrastructure (Aii) is an independent, national research and educational organization working to advance innovation across industry and public policy. The only nationwide public policy think tank dedicated to infrastructure, Aii explores the intersection of economics, law, and public policy in the areas of climate, damage prevention, eminent domain, energy, infrastructure, innovation, technology, and transportation.