A tunneling method used in Russia to run a highway beneath a train track could prove beneficial in some situations.

In 2000, highways in the United States had more than 250,000 roadway-rail crossings, according to the Federal Railroad Administration (FRA). As urban growth continues and more roads are built, this number likely will rise. Unless trains are rerouted, construction of new roads can delay rail traffic and the movement of commercial goods. Once a road is complete, trains passing through the crossing can interrupt vehicle traffic, closing the new road for minutes at a time. These delays and interruptions cause congestion and air pollution, frustrating motorists, railroad workers, and train travelers alike.

An innovative tunneling method could end this frustration and offer numerous benefits. In May 2002, a delegation of transportation officials from the Federal Highway Administration (FHWA), the Kentucky Transportation Cabinet, and the Transportation Research Center at the University of Kentucky traveled to Perm, a Russian city 1,288 kilometers (800 miles) east of Moscow, and visited a construction site where engineers have found a way to build a roadway-rail line crossing that solves many of these problems, using innovative soft-earth tunneling techniques. This method, if used elsewhere, could benefit the trains and railroad companies using the track, enhance driver mobility, increase safety, and help save money and the environment.

The Perm Solution

The City of Perm faces the same transportation problems as many cities in the United States, including heavy congestion, increasing traffic demand, highway maintenance needs, and limited funding. To help meet the traffic demand, the city is working hard to improve its transportation infrastructure. The Perm government decided that a new road with several travel lanes was needed to allow a greater traffic flow to and from the city. A complication existed, however, because a railroad crossing would be involved.

"The Perm Oblast Administration [similar to State-level government in the United States] decided to build the additional lanes as part of Perm's future transportation framework," says Vladimir Volf, deputy director of the Perm Road Committee. "We believe the project will help resolve some of Perm's transportation and pedestrian linkage problems and will help reduce congestion."

Transportation engineers faced with similar situations in the United States typically have two choices—either build an at-grade crossing where the railroad track and the new road cross at the same level or a grade-separated crossing where the new road and the railroad track are vertically separated, typically by building a vehicle bridge above the tracks. "At-grade crossings are the most common crossing methods in the United States because they are relatively easy to build and inexpensive," says Anthony Caserta, senior tunnel engineer at FHWA. Both methods typically require railroad traffic to be stopped or rerouted during construction. After construction, vehicle traffic must stop when trains pass through the at-grade crossings.

Engineers in Perm also evaluated a third option—to build a temporary railroad bridge adjacent to the existing railroad embankment. Railroad traffic then would be diverted over the temporary railroad bridge while the tunnels were constructed through the original embankment. After completion, rail traffic would be redirected over the original railroad embankment, and the temporary overpass would be removed. However, this method could be costly and might take a long time to complete.

In Perm, train traffic on the Trans-Siberian Railway (TRANSSIB) could not be stopped during construction because the rail line plays such an important role in Russia's transportation network. After construction, the new vehicle road would be heavily traveled, and stopping traffic at an at-grade crossing could cause long delays and congestion. Therefore, rather than build an at-grade crossing, a new overpass, or a temporary railroad bridge, engineers decided to construct a different type of grade-separated crossing, using two vehicle tunnels carrying multiple lanes of traffic passing through the existing railroad embankment. To accomplish this, the engineers would employ innovative tunneling techniques, used successfully twice before on two other railroad crossing projects in Perm. Land and workspace were very limited at this site, meaning that the innovative tunneling techniques would be ideal.

"We chose to build the tunnels because we estimated that construction would be faster and less costly than for the other options," says Volf. "We also felt that building the tunnels would provide better conditions for continuous rail operations and maintenance during the construction phase, and would be safer for vehicle traffic."

This tunneling method normally is not used in the United States because construction of traditional grade-separated crossings is less expensive than building tunnels and sufficient land typically is available to build grade-separated crossings. One of the only times this technique has been used in the United States was not for a railroad crossing, but rather for a tunnel that runs beneath the Mount Baker neighborhood of Seattle, WA. The tunnel, which was completed in the early 1980s, is the world's largest-diameter soft-earth tunnel. Like the new tunnels at Perm, the Mount Baker Ridge Tunnel was cut through soil, rather than rock, to form new travel lanes along Interstate 90.

Safety First

In Perm, construction of the first vehicle tunnel for the lanes in one direction began in September 2001 and was completed in December 2002. The second tunnel for the other lanes was started in September 2002, and completion is expected in October 2003.

Building the tunnels through the embankment posed unique safety challenges. The engineers had to ensure that rail traffic could pass safely over the project site throughout the construction period. Second, project engineers discovered that the embankment soils were composed primarily of dusty and medium-grain sand and would require stabilization. The third challenge was the utility lines in the area that could pose a danger if they were compromised during construction.

To overcome these obstacles, special steel supports were added to the tracks to serve as a temporary bridge should the embankment collapse during excavation. Next, holes were bored into the ground horizontally and vertically. Perforated pipes were driven into the holes and filled with a formaldehyde resin that was cured with oxalic acid. This resin was chosen because of its high penetrability, an important factor when stabilizing sandy soils. The filled pipes help prevent any settling that might occur in the soil once the tunnels are complete. Finally, surrounding utility lines were rerouted during construction.

Digging Deep

With the appropriate safety precautions in place, excavation on the first and second tunnels began. First, steel tubes were inserted horizontally into the soil, with steel girders installed to support the tubes during insertion, and then a hydraulic jet was used to remove the soil from the tubes. The steel tubes were inserted into the ground in an oval shape to serve as the walls, floor, and roof of the tunnel. As added support beneath the tunnel, jet-grouting piles were driven into the foundation.

With the tubes and piles in place, a high-slump concrete was pumped into the tubes. Next, the rest of the soil inside the tunnel was excavated. Once the soil was removed, the tubes were encased in concrete to create an aesthetically pleasing appearance.

During construction of the tunnels, workspace was limited and traffic was rerouted. Access to the worksite was possible only through a temporary road of precast panels constructed specifically for the project. To ensure the safety of the rerouted traffic and the motorists traveling on the new access road, the slopes leading to the work area were stabilized with the same method used for stabilizing the railroad embankment: tubes filled with resin inserted into the slope. The engineers used shotcrete—concrete pneumatically projected at a high velocity—on the exterior of the slope to help with stabilization.

Reaping the Benefits

By choosing to build the tunnels through the embankment, the engineers provided a number of benefits for Perm. As mentioned, this method allows train traffic to continue while the tunnels are being built, so that no delays in the transport of people or goods occur during the construction phase. Construction of at-grade or grade-separated crossings can sometimes last for several months and disrupt train traffic much of the time. The mobility benefits will continue with the completion of the Perm project, as vehicles will not need to stop to allow train traffic to pass, saving drivers time and reducing frustration.

Building tunnels rather than at-grade crossings provides safety benefits as well. To provide an idea of the potential scale of those benefits, statistics in the United States indicate that approximately 400 highway-rail crossing fatalities and 3,500 highway-rail incidents occurred in 2000, according to FRA. Installation of tunnels rather than at-grade crossings could reduce the incidence of roadway fatalities, one objective of FHWA's "vital few" goals.

Grade-separated crossings also pose safety hazards. Volf explains, "Large bridges are more dangerous from the point of view of vehicle accidents than tunnels. They also are more difficult to maintain and repair."

In addition, when traffic crosses bridges erected over rail lines, debris can be thrown from vehicles or fall from them and potentially land on the tracks, endangering oncoming trains. For some grade-separated crossings, fencing can be erected around the bridge to prevent debris from falling, but fencing installation can be prohibitively expensive. Railroad officials also are concerned about the possibility of incidents occurring on vehicle bridges that could compromise the bridge and the rail line's safety. Tunnels avoid these problems, thereby enhancing driver and rail line safety.

Another advantage of building tunnels versus overpasses is that tunnels require less land. Grade-separated crossings need high vertical clearances for the vehicle bridges and long, steep ramps up to the overpasses. Building tunnels conserves land that would otherwise be needed for the ramps.

Volf adds, "The tunnels are less intrusive than a vehicle bridge. The design is context-sensitive, and aesthetically it is a better fit for the area."

Tunneling also helps with project planning and implementation. "Railways have major liability concerns about using the land adjacent to their lines," says FHWA's Caserta. "This tunneling method uses less of the railroad's property, potentially making the railroad more agreeable to the project." Railroad officials also object to grade-separated crossings because they are reluctant to forfeit the air space above the tracks. The railroads like to keep the air space clear should they need to install cables or other aerial structures above the tracks in the future.

Financially, construction costs for a tunneling project in the United States would be the same, if not higher, than for other types of grade-separated crossings. In Russia, however, the Perm Road Committee believed that construction costs actually would be lower than for construction of another type of grade-separated crossing, given the costs of disrupting rail traffic for several months. Manufacturing companies, the shipping industry, the receiving companies, and the railroads could lose significant income, which might equal the cost of building the tunnels.

Financial benefits also could result from the reduced traffic delays and congestion that would occur if an at-grade crossing had been built. In the United States, congestion costs the average peak road traveler more than $1,000 each year. Environmentally, reduced congestion and traffic at the crossing also will result in fewer vehicle emissions, helping to reduce air pollution and improve air quality.

A Possibility In the United States?

According to the U.S. Delegation to Perm, this type of project could be implemented in the United States and could be beneficial in many regions. "The innovative tunneling method would be of great use in urban locations where construction areas are often tight and there is no room to build a typical grade-separated crossing," says Kevin Sandefur, transportation engineering specialist with the Kentucky Transportation Cabinet.

This type of solution could be used wherever the new road would serve as the primary transportation route into or out of an area. Traffic delays caused by railroad crossings on these primary roads can pose additional safety concerns. Emergency vehicles could be delayed by a blocked crossing and have no other way to reach their destination. Emergency evacuations also could be delayed if a train blocked a crossing.

Sandefur notes, however, that at least three concerns need to be addressed before this solution could be implemented in the United States. First, questions would probably arise over the safest way to stabilize the soils. Neither the Perm municipal government, nor the Russian government, appears to have developed regulations or standards for soil stabilization that could be used as guidance for similar projects in the United States.

Cost would be the second issue. Tunneling projects such as this can be expensive, especially when compared to the other crossing options. However, cost-benefit analysis of certain project sites could show that the economic benefits from enabling train traffic to continue during construction and reducing congestion after construction could outweigh the high upfront construction costs.

Third, drainage issues would need to be addressed to prevent low spots from forming in the foundation.

Although these issues and others need to be resolved before this kind of technique could be used in the United States, research to investigate the use of tunnels and these tunneling techniques for roadway-rail crossings could prove worthwhile in the end. "Any project using these techniques must be approached with great care," says Sandefur, "but the potential for a challenging and rewarding project is great as well."

Photos by issam Harik, Ralph Palmer, Tep Hopwood, and Tracy Busch.

Tracy N. Busch has 9 years of experience facilitating international cooperation in the highway sector. Seven of these years are with FHWA's Office of International Programs (1993-1995, 1997-present). Presently, Busch manages FHWA's Russian and Baltic programs. The goal of these programs is to facilitate the development of Technology Exchange Centers in Russia and the Baltics, and "'twinning" relationships between Russian and U.S. States. The six States presently involved in this outreach effort are Kentucky, Maine, Maryland, Minnesota, North Carolina, and Pennsylvania.

Keri A. Funderburg is a contract writer for FHWA and a contributing editor with Public Roads.

For more information, contact Tracy Busch at tracy.busch@fhwa.dot.gov or 202-366-9807.