Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The latest general information on the Coronavirus Disease 2019 (COVID-19) is available on Coronavirus.gov. For USDOT specific COVID-19 resources, please visit our page.

United States Department of Transportation United States Department of Transportation

Public Roads - Autumn 2021

Date:
Autumn 2021
Issue No:
Vol. 85 No. 3
Publication Number:
FHWA-HRT-22-001
Table of Contents

Safety on Ice

by Adam Larsen and Billy Connor

Frozen rivers and lakes provide natural, relatively smooth trails for walking and pulling sledges. As a result, they have served as important transportation corridors for thousands of years in the circumpolar north.

The sled dog originated in Russia several thousand years ago and eventually came into use in North America. Because dogs pulling sleds move much more quickly than a person on foot, the dogs and their owners could fall through thin ice before they have time to see it. Luckily, stories abound concerning the innate ability of dogs to sense and avoid thin ice, thus cementing a strong bond between the handler and the dogs.

While the modern snowmobile was patented in 1916, it did not become popular until the 1960s with the introduction of lightweight frames. These speedy, highly maneuverable machines rapidly replaced the sled dog. Traveling at speeds that exceed 100 miles (160 kilometers) per hour, riders could find themselves on thin ice before they could take evasive action. Riders rely on word of mouth and an intimate knowledge of local rivers to avoid danger, because few of the rivers offer markings that identify safe routes. Consequently, fatalities occur every winter as unwary travelers fall through the ice.

More recently, ice roads have carried passenger vehicles as well as heavy freight vehicles. As the weight of the vehicles increases, the danger of falling through the ice also increases. Vehicle recovery also becomes increasingly difficult.

The effects of climate change and shifts in weather patterns have also impacted ice roads. Shorter ice road “seasons” and warm mid-winter storms can make ice roads even more hazardous. These challenges will require more frequent inspections of ice thickness during and after winter storms, and may limit the length of the ice roads that can be built and maintained.

Despite these dangers, ice roads continue to be a common transportation corridor in the north. They provide an efficient means of moving supplies, equipment, people, and resources such as gravel between communities and commercial operations that are inaccessible by roads. For example, the ice road on the Kuskokwim River enables freight to be distributed from Bethel, AK, to surrounding villages at a cost significantly lower than that of moving freight solely by air.

"Aerial photograph of a frozen river near Bethel, Alaska. Image source: FHWA."
Ice roads are essential to local accessibility in Alaska and other northern regions, but present challenges in establishing and maintaining them safely and efficiently. Here, the ice road created on the frozen Kuskokwim River in Alaska is seen from the air.
"Vehicles clear snow off a seasonal road created on a frozen river in Alaska. Image source: © 2021 Nathan Belz, University of Alaska Fairbanks."
To maintain ice roads, like this one near Bethel, AK, crews must clear snow and check for hazards like cracks and thin ice.

An example of the increased use of ice roads is the river crossing at Tanana, AK, which connects a newly constructed road on the south side of the Yukon River to the village of Tanana on the north side. The ice road connects Tanana to the rest of the Alaskan highway network, reducing the cost of freight coming into the community.

To address the challenges of safely using and maintaining ice roads, the Federal Highway Administration’s Office of Tribal Transportation hosted a peer exchange and initiated an ice road research project with the University of Alaska Fairbanks to develop a guide for establishing and maintaining ice roads.

Ice Road Peer Exchange 

In March 2020, FHWA’s Office of Tribal Transportation, the Bureau of Indian Affairs, and the Center for Safety Equity in Transportation at the University of Alaska Fairbanks facilitated a peer exchange on ice roads. The discussion brought together representatives from 17 Tribes from southwest Alaska and centered around the construction, operation, and benefits of ice roads.

One speaker at the meeting was Mark Leary, the director of development and operations for the Native Village of Napaimute in Alaska, who leads the annual effort to clear the frozen Kuskokwim River and create the ice road. In most years, Leary and his crew can establish an average of 200 miles (320 kilometers) of ice road. In 2020, they set a record by clearing and maintaining the river from Tuntutuliak to Sleetmute, a distance of about 355 miles (571 kilometers). Communities along the ice road provide what assistance they can, including fuel, equipment, lodging, and manpower.

Attendees of the peer review listened raptly as Mr. Leary described his experiences in the construction of the ice road. “With few resources and little time, he and his team accomplished a near miracle,” says FHWA’s Todd Brockmann. “Even more impressive, Mr. Leary drew on his knowledge of the river and what he learned from the literature published by the Canadian ice road operators and talking to others.”

The longer ice road caused an immediate impact on the villages it served. Air freight flown into the main airport at the hub city of Bethel on large aircraft could be ferried from Bethel to communities along the ice road in all but the most extreme weather—instead of being flown in on light aircraft when that method was not made impossible by the fickle weather of the Lower Kuskokwim. This resulted in a significant cost savings for freight between Bethel and the villages.

The ice road also enables other critical services such as mail delivery, access by the State troopers, and medical services. In addition, village residents can access the hospital and other government services in Bethel even when air taxis are grounded. The Alaska Department of Transportation and Public Facilities acknowledged the public transportation benefit of ice roads in 2020 by contributing both State and Federal funding toward the construction, maintenance, and operation of the Kuskokwim Ice Road.

"A presentation to a large office in a conference room. Image source: FHWA."

Representatives from FHWA, villages served by the Kuskokwim Ice Road, the Bureau of Indian Affairs, and the University of Alaska Fairbanks met in Bethel, AK, for a peer exchange in March 2020.

At the peer exchange, as representatives from several of the communities affected by the ice road told their stories, it became clear that the ice road meant more than the lower cost of freight. Community members commented that the ice road is a source of pride for the communities along the route, creating a bond that few other projects could ever produce.

The ice road also freed communities from the unpredictable weather that makes air traffic unreliable. Ice roads offer not only the prospect of dependable freight movement, but also an alternative to air medivac for the sick or injured when the weather does not allow flights. Other community members discussed the ability to visit friends and relatives and attend regional events, such as watching their children play basketball in the next village.

In short, the ice road means freedom to safely travel along the river in winter as well as in summer, when the river enables travel by boat or barge and all-terrain vehicles provide overland travel on trails that are impassable in winter.

Addressing Challenges in Ice Road Design 

The FHWA Office of Tribal Transportation understands the importance of ice roads to communities along Alaskan rivers. While the work of people like Mark Leary and his crew is impressive, the lack of standards poses a potential public safety concern. Standards include the determination of ice thickness required to carry the expected traffic and the selection of routes, maintenance standards, speed limits, and traffic control devices.

To address this gap, the Office of Tribal Transportation has published information on how to establish and maintain ice roads in the Tribal Transportation Program Delivery Guide, available at https://highways.dot.gov/federal-lands/programs-tribal/guide/tribal-transportation-program-delivery-guide. In addition, the FHWA Office of Federal Lands Highway is funding research to establish these standards, and has selected the University of Alaska to lead the effort.

The variability in the ice and river characteristics throughout the winter months creates one of the most challenging environments in which to design, construct, and maintain a transportation corridor. The safety of an ice road requires an understanding of the properties of ice, which vary with how it was formed, its temperature, and the rate at which it is loaded (vehicle speed). How to design, construct, and maintain ice roads can vary from a highly mathematical approach based on ice mechanics and structural analysis of plates to a fully empirical approach based on the experience of those involved. In practice, the process blends these two approaches because of the variability of ice type and thickness along the routes and because of the changing characteristics of the rivers.

"A man uses an auger to drill a hole in the ice to measure its thickness. Image source: © 2021 Nathan Belz, University of Alaska Fairbanks."

The thickness of the ice can be measured using an auger, as shown here, but this method enables monitoring only at individual locations.
"An ice core sample held up to the sky. Image source: © 2020 Svetlana Stuefer, University of Alaska Fairbanks."
Taking a core sample of ice, like this one from the Tanana Ice Bridge, provides information about the quality and type of ice in addition to measuring the thickness.

As part of the research effort, the team conducted a literature review of existing guidelines such as those developed in Canada for Alberta, the Northwest Territories, and Nunavut. The literature shows that the most common design for ice roads derives from mathematical equations tempered with empirical coefficients based on acceptable risk levels. The use of a risk management framework provides a means of balancing user needs and requirements with the resources available to the ice road operators. The final design depends on the type of ice, ice thickness, anticipated ice temperatures, vehicle weights, and traffic speeds. Ice road operators can manage all of these factors except the type of ice and its temperature.

Ice thickness must be continuously monitored during road construction and throughout the winter. One of the most common methods of monitoring the ice thickness is simply to drill a small hole in the ice using small hand or powered augers. A thickness gauge with a hook attached to the bottom is then fed through the ice and pulled up against the bottom of the ice. While this method is accurate, it only allows for the measurement of ice at discrete points.

Ground-penetrating radar (GPR), commonly used to obtained continuous ice thickness, proves to be a helpful tool but has limitations. While GPR can identify individual layers, it cannot distinguish one type of ice from another. Nor is it useful when water flows over the surface of the ice or between ice layers. Consequently, GPR is best used in conjunction with conventional ice assessments and thickness measurements.

Generally, the thickness of the ice as the river or lake freezes and human experience dictates the routing of ice roads. Alaska’s rivers are geologically young. As a result, their channels change frequently, which alters the optimal routing each year. Further, the routing may vary through the winter if the thickness of the ice falls below minimal thickness because of water conditions, or if cracking occurs as the result of loading.

Cracking from vehicle loading constitutes a major safety hazard to travelers because of the danger of falling through the ice. While ice thickness, vehicle weight, and vehicle speed help manage this risk, cracking can and does occur. In these cases, agencies can apply remediation and repair techniques such as surface flooding to increase the thickness of the ice and in effect glue the cracks together. If cracking is severe enough, the location of the ice road may change.

"A man kneeling on ice holds his hand over a ground-penetrating radar unit that is attached to the back of a vehicle. Image source: FHWA."

Ground-penetrating radar (GPR) can quickly map ice depth, but does not distinguish one type of ice from another and cannot work if water flows over the ice or between the layers.

Unmanned aerial vehicles (UAVs)—or drones—fitted with the appropriate sensors can scout appropriate routes and detect thin ice and cracks in the ice without putting workers in harm’s way. The use of UAVs for this purpose is fairly new. As part of the research project, the University of Alaska Fairbanks will investigate which sensors may be required and which aircraft are appropriate for the task. UAV data will likely be used in concert with GPR and ice thickness measurements to assess the health of the ice sheet.

Signage for Ice Road Safety 

Keeping the public safe on the ice continues to be the greatest challenge of creating and maintaining ice roads. Ice conditions, speed limits, weight restrictions, and delineation all require constant communication with the public. Signage offers a critical tool in that communication. Signs at entry points can show the level of risk and remind travelers to check public information sources and any other necessary warnings. While there are a few existing destination signs and warning signs in use, these signs do not meet current signage standards. Improved signs meeting the requirements in the Manual on Uniform Traffic Control Devices, including the sign size, color, and placement, are expected to be installed during the winter of 2022.

Founding these devices on the ice presents unique challenges. While signposts can be embedded in the ice, they must be removed before spring thaw. The timing is critical because the signs need to remain in place as long as safely possible. If the operators wait too long, the signs cannot be safely removed and will be lost. While general guidance can be given, the timing will vary each year based on conditions and must rely on the judgment of the operator.

"A large red sign reads “Danger, go slow” with an arrow pointing to the right. Image source: © Mark Leary, Native Village of Napaimute."

The temporary signs, like this one, warn drivers about hazards on the ice roads. 

Signage for speed limits is critical. Speed limits on ice roads not only ensure that the vehicle can traverse the route, but also serve to protect travelers and the road itself. Following maximum speed postings guarantees that the ice does not break because of the wave that is generated in the water ahead of the loading. If the speed is too great, the wave becomes large enough to generate tension in the surface of the ice, which results in radial cracking. Radial cracking provides the last warning before the vehicle falls through the ice.

Public Information 

Hazardous conditions, like open holes and thin ice, can develop throughout the winter. Travelers on the ice roads need to be aware of these conditions. Local crews or operators will commonly mark hazardous areas using willows around the perimeter of the hazard. In some cases, these willows are wrapped with reflective tape to improve visibility during the long hours of winter darkness. Social media is also used to spread the word about incidents and hazards. However, no formal system currently exists for distributing public information about ice road conditions.

FHWA’s Tribal Transportation Program Safety Fund awarded a grant to the Native Village of Napaimute to develop a public information app or website. In partnership with other entities involved in the management of the ice roads, the village hopes to deploy a pilot of the system by the end of 2021.

"A sign beside the ice road reads, “Warning: Trail conditions change. Travel at your own risk. To report trail conditions call 545-2877.” A handmade wooden arrow marked with the letters K L G is attached to the sign post below the sign. Image source: © Mark Leary, Native Village of Napaimute."

Warning signs remind travelers that road conditions may change. The arrow marked KLG indicates the direction of Kalskag, AK.

The Future of Ice Roads 

Construction and operation of ice roads present numerous challenges. After listening to the users of the Kuskokwim River Ice Road, it is clear that the value of ice roads to village residents far exceeds the costs associated with the road. While some costs, such as freight expenses can be quantified, the benefits of watching a child play basketball or visiting friends and family in adjacent villages cannot be calculated.

The cost of conventional roads makes their construction in the region unlikely. Consequently, river, trail, and air travel offer the only viable options.

The FHWA Office of Tribal Transportation and the University of Alaska’s Arctic Infrastructure Development Center recognize the need for uniform practices related to the design, construction, and operation of ice roads. The manual being developed under FHWA funding will help ensure the safety of those who are increasingly dependent on ice roads.

Adam Larsen is the safety program manager with the FHWA Office of Tribal Transportation. He holds a B.S. in civil engineering from Portland State University.

Billy Connor is a professional engineer at the Arctic Infrastructure Development Center at the University of Alaska Fairbanks. He holds a B.S. in civil engineering and an M.S. in engineering science management from the University of Alaska Fairbanks.

For more information, see https://cset.uaf.edu or contact Adam Larsen at 306-619-2601 or adam.larsen@dot.gov or Billy Connor at 907-474-5550 or bgconnor@alaska.edu.