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.

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26 Responses to What Happens After a Rock Hits a BC Highway

  1. tim on March 30, 2015 at 7:13 pm

    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.

    • tranbceditor on March 31, 2015 at 9:29 am

      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.

  2. Nicholas Thomas on April 2, 2015 at 1:19 pm

    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.

    • tranbceditor on April 2, 2015 at 4:12 pm

      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.

    • tranbceditor on April 7, 2015 at 11:43 am

      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.

      • Nicholas Thomas on April 7, 2015 at 2:57 pm

        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.

      • Nicholas Thomas on April 7, 2015 at 3:08 pm

        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.

  3. Nicholas Thomas on April 2, 2015 at 4:24 pm

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

    • tranbceditor on April 7, 2015 at 9:37 am

      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.

  4. Callie Marie on August 6, 2015 at 3:22 pm

    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.

  5. Ashley Trashley on April 18, 2016 at 1:23 pm

    In regards to the previous posts about 3 valley gap l would like to add that I also have known this to be a problem area. There is always rock on road when I drive through and especially avoid the area at night. I have not ever seen or heard of any ‘mitigation’ either…. so curious as to what exactly was purchased with 1 million dollar budget?

    • tranbceditor on April 20, 2016 at 2:44 pm

      Hi Ashley,

      We have sent your question forward to the local area manager for an answer. Stay tuned.

  6. Ashley Trashley on April 23, 2016 at 12:38 pm

    And How long will I need to stay tuned for?

    • tranbceditor on April 25, 2016 at 12:00 pm

      Hi again Ashley,

      Many rock slope stabilization activities do not leave an obvious visible footprint after it is done. Some of the stabilization activities that have been performed at Three Valley Gap include:

      Rock Scaling – to remove loose rock from slope by workers (rock scalers) suspended on ropes using pry bars
      Trim Blasting – has been performed to remove rock from the slope by drilling holes into it and loading with explosive and blasting.
      Shotcrete – has been applied which is sprayed concrete that is used to prevent rocks from loosening.
      Horizontal Drains – have been installed to lower water pressure to improve stability
      Rock Bolting – rock bolts have been installed to hold large blocks of rock in place. Rock bolts are steel bars cemented in drill holes and tensioned.
      Slope Mesh – slope meshing is used to direct rockfall into the highway ditch

      Many of these activities are done high on the slope and are not easily visible from highway level.

      • Ashley Trashley on April 28, 2016 at 7:07 am

        thanks for your response.
        and maybe not but the traffic control would be an indicator that there was work being done in the area, even if we ” couldn’t see them up on the slope”. we would see the road closed to some extent for safety measures. to avoid rocks being scaled, etc. onto motorists. when were these activities claimed to have been done i wonder cuz I frequent this area and can’t seem to recall……
        but I’m sure I just didn’t notice…..

        • tranbceditor on April 28, 2016 at 10:14 am

          Hi Ashley,

          The last major phase of stabilization work that would have caused significant traffic disruptions was in done 2004. Smaller less disruptive work was done as recently as 2012.

  7. Ashley Trashleys blasting on April 29, 2016 at 12:24 am

    haha 2004?!do they take in consideration the freeze and thaw factor? that’s over ten years ago!
    as for 2012 I’m curious as to who the contractor was so I can know who’s substandard work it was…. paving over the the holes made from poor slope stability Doesn’t count by the way 🙂

    • tranbceditor on May 4, 2016 at 11:50 am

      Hi Ashley,
      Thanks for your continued interest in the work we do to keep BC highways safe. The safety of the travelling public is our first priority. Since the 1970’s we have had a dedicated stabilization program aimed at reducing rockfall on BC Highways. With BC’s mountainous terrain and changing weather conditions it is not possible to prevent all rockfalls from occurring as it would be cost prohibitive to do so.

      Our geo-technical engineers monitor the stabilization work our contractors do on BC highways to ensure that our standards are being met. We try to coordinate stabilization activities in advance of paving projects whenever possible.

  8. Ashley Trashley on April 29, 2016 at 9:39 pm

    looks like someone can’t handle the heat and is not allowing some of my posts?? hmmmmmm
    Honesty is the best policy!

  9. Ashley Trashley on May 4, 2016 at 3:42 pm

    Hi TranBC
    Thank you for dancing around my questions. Also, thank you for informing me that you are unable to prevent all rockfall I will put that in my back pocket for later. In the future however if you are unaware of the answer to one of the questions you should just ask me!

  10. Ashley Trashley on May 23, 2016 at 6:56 pm

    Highway 1 Both directions
    Watch for Rock on Road at Three Valley Gap. Updated on Mon May 23 at 4:02 pm PDT. (ID# 220134) [View on map]
    2016-05-23 4:02 PM

    compliments of drivebc

    ohhhhhhh snap

  11. Bob on August 29, 2016 at 9:55 am

    Get over yourself Ashley. There isn’t an unlimited budget for this kind of stuff.

    • Ashley Trashley on October 23, 2016 at 4:50 am

      No need to be so hasty….. Is there really an unlimited budget for anything, Bob? 🙂
      But more importantly why does my genuine concern for the safety of the general public, yourself included, seem to bother you so much?

  12. Anonymous on September 26, 2016 at 12:53 am

    Not only that ashley…being a rock scaler myself i can say that nobody can ever prevent ALL rockfall.. Your foot must be in your mouth because of the work currently being done at 3 valley gap 🙂

    • Ashley Trashley on October 23, 2016 at 4:41 am

      the preventing all rockfall comment was a PURELY sarcastic comment (which I felt was obvious), as I fancy myself to be a bit of a wisenheimer.
      I assumed the inability to prevent all rockfall was common knowledge, I apologize …..that was wrong of me. 🙂
      Also, I appreciate your concern but my foot is nowhere near my mouth as the first time I commented on this matter was April 18, and I did not hear of any work going on there until sometime in September.I also prefer stretching prior to such a maneuver.

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