What Happens After a Rock Hits a BC Highway

Geo Assess Engineers

Rockfalls tend to happen more often in spring, when slopes above highways can be affected by changing temperatures and increased rainfall.

The Ministry of Transportation and Infrastructure’s Rockwork Program uses a variety of techniques to keep rock and debris off highways. But rockfalls are a natural process and cannot always be prevented. In those cases, the ministry and its maintenance contractors spring into action to ensure the highway is cleared and safe for travellers.

Reporting a Rockfall

Maintenance Contractors routinely patrol highways to ensure they are clear of debris such as rockfall.   If you happen to come across a rockfall, it’s best to stay in your vehicle and contact the local maintenance contractor. Use your mobile phone to access the Report a Problem mobile site, which will help you identify what phone number to call. For more information about what types of highway problems should be reported this way, and to view a map showing highway maintenance contractors by region, visit the maintenance contractor webpage.

Clearing a Minor Rockfall

Most rockfalls are small (about the size of a fist), and can be quickly cleared from the highway by the local maintenance contractor, who documents the event and submits the information to the ministry.

Assessing and Clearing a Major Rockfall Site

Lytton rock slideReopening a highway after a rockfall isn’t always as simple as clearing the rock and/or debris off the road. Some are extensive enough that a geotechnical site assessment of the slope is performed to ensure clean-up crews can clear the highway safely, and travellers can use the highway safely. The key word here is “safely.”

In these cases, a member of the ministry’s geotechnical engineering team will conduct an assessment, either by:

  • Reviewing the site at ground level
  • Walking the slope
  • Aerial assessment by helicopter (depends on weather conditions)

The maintenance contractor can begin clearing the highway if the slope is secure. Depending on the size of the fallen boulders, blasting and/or drilling may be needed to break them into moveable pieces. We saw this back in January 2015, when a 7ft by 7ft rock fell on Highway 12 near Lytton.

On the other hand, slope stabilization work may be required.

Stabilizing the Slope

The Rockwork Program uses various slope stabilizing methods depending on the site conditions .

  • Rock Scaling: removing loose rock from slope by workers (rock scalers) suspended on ropes using pry bars.
  • Trim Blasting: used to remove rock from the slope by drilling holes into it and loading with explosive.
  • Rock Bolting: rock bolts are installed to hold large blocks of rock in place. Rock bolts are steel bars cemented in drill holes and tensioned.
  • Slope Mesh: used to direct small rocks into the highway ditch.
  • Shotcrete: sprayed concrete used to prevent rocks from loosening.
  • Horizontal Drains: used to lower water pressure in slopes.
  • Catch Fences: used to intercept high energy rockfalls.

Rock slide hazardRockfalls aren’t always caused by rainfall and changing temperatures. For example, growing tree roots, forest fires, and animal activity can also become triggers. The “Watch for Falling Rocks/Debris on Road” roadside sign indicates a location where there is a rockfall risk. If you come across this sign, or if you are driving through any rock slope area, pay attention and watch for debris on the road ahead. And, of course, it’s not an ideal place to pull over.

British Columbia’s mountainous landscape means our highways pass through some challenging terrain. The ministry’s Rockfall Program is dedicated to reducing the rockfall hazard for highway travellers.


National Engineering Month TranBC Trivia: What area of BC do rockfalls happen the most? Post your answer to the comments section below.

Page 1 of 46 comments on “What Happens After a Rock Hits a BC Highway”

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  1. I drive through a twisty canyon every time I go visit my grandma. There are a few “rock fall” signs on the road, so I am always paranoid about it happening while I’m driving. From now on, I will pay close attention to the road, in case there are any rocks that have fallen already.

  2. I did comment on this blog and the post stayed there ‘waiting for moderation’ for a while. Then it disappeared.

    • Hi Nicholas,
      That’s very odd and I’m sorry that happened. We do have a moderation policy (linked at the top left of the blog) so we make sure comments meet those requirements (ie not sexist, racist, etc.). Didn’t see anything from you on this blog beyond these latest comments. Thanks for reposting to make sure we saw it.

  3. Repeating my comments that seem to have disappeared.

    Are there any plans to do anything about rockfall at Three Valley on the Trans-Canada? Last fall a rock went through the trailer of a commercial transport. If it had been 50 feet further forward it would have killed or seriously injured the driver. Since then there has been another fall of rocks easily big enough to kill, although I think they stopped JUST short of the highway.

    • Hi Nicholas, Thanks for the question.
      Sorry if you haven’t seen them but we haven’t removed any of your previous comments. We only do so if they fall outside our moderation policy. They’re all still on the various blogs you’ve previously commented on. This is the first you’ve commented on this blog however.
      In regards to rockfall at Three Valley Valley, I’ll connect with our rockwork team to share what we’re doing in that area.

    • Hi Nicholas,
      Regarding your comment, our ministry has a dedicated maintenance program aimed at reducing rockfall hazards throughout the province. More than $1 million has been invested in rockfall mitigation measures at Three Valley Gap and we’ll continue to monitor conditions there, doing additional work based on provincial rockfall priorities. We track rockfall activity along all BC highways and for significant events such as the event you refer to, we have geotechnical engineers investigate and determine the level of stabilization work needed.

      • That is interesting because I don’t remember any rock scaling or other mitigation work being done at Three Valley in the last 7 years. The only ‘mitigation’ I am aware of is debris removal from the travel lanes and the ditches. Oh and I think there was some renewal of the EXISTING lock blocks.

      • N.B. Both the rockfalls I mentioned happened East of the lockblock wall, as did another very serious rock fall that happened a few years ago. So the lockblock wall didn’t help.

    • I lost my father in the 80s to a rock scaling accident at 3 Valley Gap.This section of highway has proved to be a nightmare to maintain and navigate.Common sense would say design higher kn fencing and supports and cage the monster in.

      • Hi Anonymous,

        Sorry to hear of the loss of your father while working at 3 Valley Gap.

        Safety in Three Valley Gap near Revelstoke is a priority for our ministry. However, while typical rock slope stabilization involves rock scaling, rock blasting and slope meshing, standard rock fall fences can’t withstand the snow loads and snow avalanches at Three Valley Gap.

        I’m looking for the latest information, on a new rock fall fence system we have in the works for testing at Three Valley Gap. I’ll get back to you here, with an update, when I have it.

        • Hi Anonymous,

          Our new rock fall fence system is now 90 per cent finished.

          It’s designed to minimize the risk of damage from snow loading and avalanche activity, without compromising the effectiveness of our remote avalanche control system. The project is in shut-down now during winter and final completion will occur in the spring. The new fence will improve rockfall protection this winter, even in its unfinished state.

          If the pilot is successful, we will consider this type of system for other rockfall areas in the Three Valley Gap.

          In addition, a new 33-metre-long lock block retention wall was installed in autumn, to reduce the risk of large boulders falling onto the road.

  4. When is the MoT&I going to improve BCHwy14 from the 4 lanes to Kangaroo Rd? This stretch of road is in bad shape and has rocks on the road way daily. There is no cell service in this area. The highway really really needs improvements badly on this 1.4 km section.

    • Hi Tim,

      Thanks for sharing your concern with us. We have sent your comments forward to the area office and will let you know what we hear back.