“Don’t judge a book by its cover.”

This little piece of everyday wisdom guides the work of railroad bridge engineers at the Transportation Technology Center, Inc., or TTCI, the freight railroad industry’s research and test center in Pueblo, Colorado.

“Right now we have three steel [bridge] spans at our test facility that are over 100 years old,” says Dr. Duane Otter, principal engineer at TTCI. “They may be old but we’re finding that many old bridges like these are safe and strong — well beyond the lifespan that was envisioned when they were first built.”

Dr. Otter credits railroad bridge health and longevity to generations of railroad bridge engineers who took a conservative design approach to build bridges that could carry the immense weight of steam-powered locomotives. Some of these original iron horses placed tremendous stress on rail bridges in the early 20th century. Today’s environmentally friendly modern locomotives place less stress on railroad bridges.

In the years since the early 1900’s, the railroads have closely monitored locomotive and car weights. The industry’s conservative approach to bridge construction — and maintenance and inspection — has been instrumental in allowing those bridges to remain in continued safe service.

Railroads have been leaders in bridge safety practices for decades. In fact, long before the federal government began its highway bridge inspection program, the railroads inspected railroad bridges routinely. These inspections require detailed annual checks of each bridge. Safety inspectors sometimes need to scale bridges — often hundreds of feet in the air — to examine the health of bridge members and components.

As the years have progressed, the traditional manual inspection process has improved with “snooper trucks” — specialty trucks fitted with a retractable arm and bucket for inspectors. The introduction of this method, still the primary approach today, sped up the process and improved inspection safety. However, it requires temporarily pausing train traffic on a portion of track in order to inspect the bridge.

Today, railroads are working to further improve the safety and efficiency of bridge inspection, aided by unmanned aerial vehicles, or drones, and other remotely controlled robotic devices. These technologies, currently being developed for freight railroad use, will allow railroads to conduct routine bridge inspections without suspending train traffic and slowing down the network. A bridge can be subject to more detailed inspection if determined necessary by the railroad bridge engineer.

Time-saving innovations like this improve the flow of rail traffic because many freight rail bridges are inspected more frequently than the Federal Railroad Administration’s annual requirement.

“Railroads have well-tested guidelines for determining the frequency of inspections based on the weight of trains, volume of train traffic, the types of traffic going over bridges — such as passengers or hazardous materials,” says Dr. Otter. “Railroads will often increase the frequency of inspections if a bridge shows initial signs of wear or tear that are significant from a safety standpoint.”

Although some bridges may look outdated to the general public, appearances are deceptive. The simple design of most railroad bridges makes them simple and efficient to repair, and that contributes to a safe, extended life.

“Just because a bridge has rust does not mean that it’s dangerous,” says Dr. Stephen Dick, principal investigator at TTCI. “On the other hand, additional aesthetic design elements, such as decorative beams or arches, can inhibit access for inspection of a bridge. For the railroads, form follows function. The work that we’re doing at TTCI has improved bridge safety standards across the industry. We take pride in ensuring that every link in our network remains safe and strong — now and for years to come.”