Worked Example: Pit and Pipe Works on a Roundabout Approach

Roundabout works traffic control is about protecting every movement through the roundabout, not just the lane being dug up. For pit and pipe works on an approach, that means an early lane closure with room for the taper, off-peak staging, a plan for lane arrows and pedestrians, a controlled plant access point and a clear reopening check before peak.

This article walks through an example job step by step. It is a teaching scenario, not a real project. The approved traffic guidance scheme (TGS), the road occupancy approval and the road authority's conditions decide what is actually done, and the TGS must be prepared by a suitably qualified person. This is general information, not legal or engineering advice. For the general principles, see roundabout roadworks traffic management.

The example site

Example scenario: a drainage contractor has to replace a collapsed stormwater pit and about 15 metres of pipe in the left lane of a two-lane approach to a four-leg roundabout. The approach is signed at 60 km/h. The pit sits close to the holding line, and a side street joins the approach a short distance upstream. There is a pedestrian crossing point across the splitter island, a bus stop on the departure side of the next leg, and a footpath along the kerb next to the pit.

The road authority's approval in this example allows the lane to be closed between the morning and afternoon peaks only. The job is expected to take two days: day one to saw-cut, excavate, locate services and set the new pit; day two to connect the pipe, backfill and reinstate.

The crew is a traffic supervisor and two controllers, with a vacuum excavation truck, an excavator, a tipper and the drainage crew. Our guide to vacuum excavation traffic management covers the vac truck's footprint and hoses.

The design problems the TGS has to solve

Before anyone books a crew, the designer and the contractor work through the problems specific to a roundabout approach:

Each of these comes from the TGS for this site. Tapers, buffers and sign spacings depend on the speed and the road, and come from AS 1742.3, the AGTTM and the state supplement, applied by the designer. Our guide to lane closure traffic plans explains how those parts fit together.

Set-up order on day one

Set-up starts at the end of the AM peak, once the road authority's window opens.

1. Pre-start and SWMS sign-on. Work on a road used by traffic is high-risk construction work, so a SWMS is required. Radio check on the agreed channel and the backup.
2. Advance warning signs on the approach, starting furthest out, at the positions on the TGS.
3. Side street signs so drivers turning out know the left lane ahead is closed.
4. Lane movement signs for the open lane, and covers on any permanent signs that conflict, as the TGS requires.
5. Taper and lane closure with cones or delineators per the TGS, working from upstream down, from the protection of the vehicle.
6. Footpath and crossing closure with pedestrian barriers and the detour signs, checked for a continuous, accessible route.
7. Work area set-out: plant positions, spoil location, the access point and the controller's station.
8. Supervisor's walk and drive-through in each direction that uses the approach, with photos.

The briefing covers the window times, the pack-down deadline (which is earlier than the window close, because pack-down takes time), the access point routine, the pedestrian detour and the rule that nobody walks across circulating traffic to reach the island.

Running the shift: access, queues and radio calls

Plant access. Trucks leaving the work area have to merge back into the open lane right at the roundabout. In this example, TC 1 is stationed at the access point. The routine is:

1. Truck driver signals ready to leave.
2. TC 1 waits for a gap in the open lane and checks circulating traffic.
3. TC 1 radios: "Truck leaving the site, holding the open lane." Approaching drivers are held for a short moment where the TGS allows.
4. Truck leaves; TC 1 releases the open lane.

Trucks arriving use the closure entry upstream and travel in the closed lane to the work area, never reversing back up the approach in live traffic. Our guide to work zone access points covers the general method.

Queue watch. TC 2 is posted where they can see the back of the queue on the approach and the side street. If the queue reaches the side street junction, TC 2 tells the supervisor. Simple triggers agreed at the briefing make the decision easy: if the queue is past the junction for more than a few cycles, plant movements pause; if it persists, the supervisor considers an early pack-down. For queue estimates before the job, try the free queue calculator.

What goes wrong in this example, and the fix:

• Services are not where the plans show. The vac truck finds a communications conduit across the pit location. The excavation pauses; the contractor contacts the asset owner. Traffic control stays in place; nobody extends the closure beyond the TGS to "make room".
• Pedestrians ignore the detour and walk along the closed lane. The supervisor adds barrier where the TGS allows and stations a controller briefly to redirect people. If the detour is genuinely too long, that goes back to the designer.
• A driver in the closed lane realises late and tries to merge at the work area. This usually means the advance signs are not doing their job. The supervisor checks visibility of the signs, especially around parked vehicles near the side street.
• The pit is not set by the pack-down deadline. The excavation is covered with steel road plates of the type and fixing the engineer specifies, with any signs the TGS requires. See steel road plates and temporary surfaces for the considerations.

Pack-down and reopening before the PM peak

Pack-down starts early enough to finish before the window closes. The order:

1. Work area made safe: excavation backfilled or plated, spoil and plant removed, surface swept.
2. Supervisor inspects the surface in the work lane, including plate edges and any level difference.
3. Footpath and crossing reopened, pedestrian barriers removed, or kept if the work area still needs protecting.
4. Lane closure removed from downstream to upstream, working from the protection of the vehicle.
5. Lane movement signs and covers removed; permanent signs uncovered.
6. Advance warning signs removed last, on the approach and the side street.
7. Drive-through of the approach to confirm the road reads normally.

Day two: same set-up, different risks

Day two uses the same TGS, but the crew should not assume it is the same job. Before the closure goes back in, the supervisor inspects the plates or backfill left overnight and records their condition. Overnight, a plate can shift under heavy vehicles, and a backfilled trench can settle.

The work on day two is pipe connection, backfill, compaction and reinstatement. That changes the plant mix: a compactor and a small truck replace the vac truck, and the spoil stockpile shrinks. The supervisor re-briefs the access routine and checks that the pedestrian detour still makes sense now that the excavation is smaller. If the crossing can safely reopen earlier, that is a change to the arrangement and goes through whoever the project nominates to approve TGS changes.

Reinstatement is the last risk. A temporary surface that is lower or higher than the lane next to it is a hazard for motorcyclists and cyclists in particular, and it sits at the point where drivers are looking right for circulating traffic rather than down at the road. The supervisor checks the finished surface before the lane reopens and records the result.

Common mistakes on roundabout approach jobs

• Fitting the taper into whatever space is left. If the closure cannot be signed and tapered properly between the side street and the pit, the closure must start earlier.
• Ignoring the side street. Drivers turning out need the same warning as drivers on the main approach.
• Packing down at the window close. Pack-down has to finish by then, so it starts well before.
• Reversing plant up the approach. Trucks leave through the access point under control, every time.
• Forgetting the crossing. If the splitter island is cut off, pedestrians will find their own route unless the TGS gives them a better one.

The shift record

In NSW practice, work-site traffic control is inspected at the start and end of every shift and at suitable intervals during it, plus after-care inspections where anything is left overnight. NSW projects now generally work to TS 05492 Traffic Control at Work Sites, which replaced the TCAWS manual on 25 June 2026; confirm which document applies with Transport for NSW. The national guidance is published by Austroads, and AS 1742.3 is available through Standards Australia.

Next steps

For your next roundabout job, list every movement through the roundabout and check how the closure affects each one before the TGS is finalised. If you run traffic control crews, TrafWise keeps pre-starts, SWMS sign-ons and signed digital dockets together for each shift, so the record above is complete when the lane reopens.