Excavator tail swing beyond the cones
You are managing a drainage repair on the wide grass verge of a 40 mph dual carriageway. The layout closes lane 1 with a 30-cone lane closure about 2.5 m wide; the works themselves are in the verge, outside the carriageway. A 13-tonne tracked excavator sits on the verge and slews through 180 degrees to load an 8-wheel tipper parked within the closure. The excavator's tail swing overhangs the cones by roughly 1.5 m into the closed lane and its bucket passes over the tipper. The banksman is standing at the rear nearside corner of the tipper, which puts him in lane 2 with his back to oncoming traffic. Traffic is heavy in both directions and several vehicles have swerved to lane 2 to pass; one sounded its horn at the banksman. The closure has been in place since 07:00; it is now 15:00.
1. Identify the controls you would stop work to put in place, and explain the reasoning for each.
Read the worked answer
Stop the loading operation and re-plan it before the next bucket.
Three separate failures are stacked here:
- The cone line is not a works boundary for the machine. A taper defines where traffic may go; it does not stop the excavator reaching over it. A 1.5 m tail swing overhang means the 'closed' lane contains a moving counterweight. Either the closure is widened to contain the full slewing envelope with a defined safety zone between that envelope and live traffic, or the slewing is restricted. Cones alone give no physical protection against an errant vehicle - for a machine this size beside a 40 mph carriageway, a positive barrier should be seriously considered, and a lane 2 closure or a hard shoulder-type separation may be the honest answer.
- The banksman is in the running lane with his back to traffic. That position provides no useful signal to the machine operator and places him directly in the path of the swerving vehicles he is supposed to be controlling. He must be in a protected position with a clear view of both the machine and approaching traffic, a means of stopping the operation, and a planned escape route.
- The loading geometry is wrong. Loading across a tipper with the bucket passing over it, with the machine close to the carriageway, means any dropped load lands near live traffic. Re-plan: load from the verge side, park the tipper fully within a protected area, restrict slew, or use a smaller machine.
No one resumes until the layout, the machine envelope and the banksman position have been re-planned and briefed.
2. Is the closure width adequate, and what other factors would you weigh in deciding whether to close lane 2 as well?
Read the worked answer
Two and a half metres of cone-marked lane is a number, not an assessment.
What matters is the space between the moving parts of the works (in this case the tail swing) and the traffic stream, and what a driver at 40 mph does if they drift. The questions to work through:
- What is the actual safety zone? Take the excavation and machine envelope, add a working area for people and materials, then add a margin for driver error that grows with speed. Here the margin is negative, because the tail swing is inside the coned area but outside the safe envelope.
- What is the consequence of an intrusion? A vehicle entering this closure meets an excavator and a tipper, not a shallow hole. That argues for physical separation rather than cones.
- Can lane 2 absorb the displaced traffic safely? Heavy two-way flow, vehicles already swerving, a banksman in the lane - the answer is visibly no. Closing lane 2 and running a single lane, or using a full carriageway closure with a diversion at low-traffic hours, may be the better trade.
- Does the closure still match the design? If the machine or method has changed since 07:00, the layout may no longer be the one that was designed.
The point to make to the client: the cost of a lane 2 closure is a delay; the cost of the alternative is a fatal accident, and the decision is not the site team's to gamble on.
3. The closure has been running for eight hours and the crew are hot, tired and behind programme. How does that change your decision-making?
Read the worked answer
It changes it towards stopping, not towards pressing on.
Fatigue and heat degrade exactly the judgements this operation depends on: the operator's awareness of the slew limit, the banksman's attention to approaching traffic, the labourers' sense of where the cone line is. The evidence is already in front of you - a banksman standing in a live lane is the sort of decision a fresh, well-supervised crew rarely makes.
Practical measures:
- Rotate roles and give breaks, with a relief banksman and a second competent operator; do not allow a single person to control traffic all day without relief.
- Re-brief at the point of change. The site conditions (traffic volume, swerving, horn) differ from the morning assumption; the risk assessment must be reviewed and the change recorded.
- Consider whether the operation should be done at a quieter time - the loading cycle is the highest-risk activity here and it may belong in a short night-time closure rather than eight hours beside a busy dual carriageway.
- Give the crew an explicit right to stop the job without needing to justify it to the project manager.
Working to programme is a legitimate pressure, but it must be resolved by changing the method or the timing - never by accepting a layout that the traffic has already shown it does not respect.