Preventing Overturn

Driving vehicles safely over rough forestry sites takes a great deal of experience and skill. All operators must have achieved an FMOC award, but this is not the end of their learning about driving forestry vehicles. Below are some of the lessons learned from past experiences and recommendations from a group of forest machinery drivers.


  • Travelling with the crane arm up raises the centre of gravity of the machine and makes it more prone to overturning.
  • Overloading the bunk can also raise the centre of gravity of the machine. Loads should be kept below the height of the bulkhead. Loading above the height of the bulkhead increases the risk of a log striking and coming through rear windows of machines.
  • Logs in bunks should be evenly loaded. If heavier logs are put at the top of a load, or all on one side the machines stability will be compromised.
  • Machines with self-levelling cabs keep the driver level whilst the machine is running over uneven ground. This isolates the driver from feeling the undulations of the ground As the cab runs over these first it gives the driver early warning before the bunk runs over the same ground. If the forwarder has this facility it should be turned off once the bunk is loaded and the timber is being extracted.


  • History has shown us that tracked machines are more vulnerable to overturn. Wheels will deflect over stumps, lessening the effect on the angle of the machine
  • Some harvesters have had a poor record of  They are very stable running up the hill but turning, side- tracking across a hillside and coming back down are when they are most at risk of overturn.
  • When descending a hill in a tracked machine hold the head back toward the machine. This keeps the weight distribution as far back as possible and helps with balance as the machine runs over rough ground.


  • Many machines overturn when one side runs over a stump.
  • This can be made worse when the opposite side is on soft ground. The extra weight that is transferred causes the side on the soft ground to dig in more.
  • Stumps on extractions routes should be removed wherever possible.
  • Brash mats should as stable as possible. Longer lengths are required on softer ground.
  • Keep stump heights as low as possible and as parallel to the ground as possible. On a steep slope there can be a significant height difference on the height of the stump from the uphill side to the down.
  • Driver experience is an important factor alongside having passed the correct ticket.

Learning Points:

  • Think about the work you are about to do each time you start a new task, or a familiar task in a new position.
  • How would you contact fellow workers on site in an emergency? If the mobile phone signal is poor or not covered what will you do?
  • If there is a high stump in or near the brash mat report it and get it removed to remove the hazard.
  • Always wear your seatbelt – if your machine overturns this could prevent injury.