Disclaimer: This article provides general educational information only. It does not constitute project-specific advice, assessment, engineering design, or certification of compliance. Requirements may vary between states, territories, road authorities, and site conditions. Designers remain responsible for verifying all designs against the applicable version of AGTTM, jurisdictional supplements, and any local authority requirements. Where containment systems or engineering judgement are required, a competent person must be engaged.
AGTTM Part 3 Excavation Requirements and Risk Factors
Excavations are common on temporary worksites and can introduce significant hazards if a vehicle leaves the travelled path.
AGTTM Part 3 guides delineation around excavations and identifies scenarios where risk levels increase, and containment may be required.
Layouts fall within the scope of Traffic Management Design. However, deeper excavations, reduced clearances, higher speeds, or higher traffic volumes may trigger consideration of escalation to a competent person, such as a Traffic Engineer.
AGTTM Section 6.8 asks designers to consider operating speed, traffic volume, excavation depth, excavation width, and clearance to the travelled path. These factors interact, and as they compound, the likelihood and consequence of a vehicle entering an excavation can increase.
AGTTM also notes that cones, barricades and unsupported mesh fencing may not be suitable where they cannot prevent pedestrian or vehicle access.
AGTTM Table 6.1 Explained: How to Determine Excavation Protection
Table 6.1 provides a structured method to identify the minimum level of protection near excavations.
It considers speed, traffic volume, clearance, and excavation depth to determine whether delineation remains appropriate or whether containment should be considered.
The table presents three outcomes:
• Option 1: Cones or bollards spaced in accordance with Section 5.4.1
• Option 2: Cones or bollards spaced at a maximum of 4 metres
• Option 3: A road safety barrier system
Options 1 and 2 align with delineation.
Option 3 indicates containment.
When Option 3 is identified, AGTTM indicates that the level of risk may warrant review or design verification by a competent person.
When Excavation Control Moves From Delineation to Containment
Many excavation layouts initially appear manageable with cones or bollards, but uncertainty often arises when several higher-risk factors occur together.
As speed increases, clearance reduces, traffic volumes rise or excavation depth becomes more significant, Table 6.1 is more likely to identify Option 3 outcomes.
A helpful way to interpret the table is that when multiple higher-risk variables are present, the design is more likely to move from delineation to containment.
This reflects how AGTTM structures its decision-making and why this particular element of excavation design is often challenging for TMDs.
When Cones and Bollards Are Typically Suitable for Excavation Delineation
In low-speed, low-volume environments with shallow excavations and adequate clearance, cones and bollards generally remain suitable.
These conditions support the delineation intent of AGTTM Part 3 and typically fall within the responsibilities of a TMD.
Excavations located well outside the travelled path, or worksites with generous lateral space, often fall into this category.
Designers should verify requirements against jurisdictional supplements, which may define hazards or acceptable treatments differently.
When Excavations May Require a Road Safety Barrier System
Barrier requirements tend to appear where excavations are deeper, closer to live traffic, or located within higher-speed or higher-volume environments.
In these conditions, delineators may not adequately prevent vehicle intrusion, and containment may be required.
AGTTM Section 5.3.1 explains that road safety barrier systems are containment devices.
Their selection and design need to consider Austroads Guide to Road Design Part 6 and AS/NZS 3845.1, which outline working width, deflection behaviour, test levels and end treatment requirements.
These are not part of the TMD role.
What AGTTM Defines as a Competent Person for Excavation and Barrier Design
A competent person is someone with the qualifications, experience and technical capability to design or verify containment systems.
This includes an understanding of barrier performance, crash testing, working width, deflection, transitions, end treatments and the jurisdictional requirements that may apply.
This is traditionally a relevantly qualified Traffic Engineer.
AGTTM makes clear that this level of assessment is outside TMD’s responsibilities.
When TMDs Should Escalate Excavation Design to a Traffic Engineer
Designers should consider escalation when Table 6.1 identifies Option 3 or when operating conditions increase the likelihood or consequence of intrusion.
This often occurs when excavations are close to the lane, present in high-speed environments, or introduce depth and width that influence the severity of a potential incident.
Limited working space and the likely need for transitions or end treatments also indicate that a competent person should verify containment design.
Escalation should be considered when one or more of the following indicators are present:
- Table 6.1 indicates Option 3
- The excavation is close to the lane
- The posted speed is 70 km/h or higher
- Traffic volumes are moderate or high
- The excavation is deep or wide
- There is limited space for a suitable buffer
- End treatments or barrier transitions are required
- AGTTM directs the user to other Austroads Guides
- State or territory supplements require higher containment
These conditions indicate that the design involves containment, rather than delineation.
State and Territory Requirements for Excavation Control (QGTTM, TCAWS, VIC CoP)
Each jurisdiction applies its own interpretation of excavation risk.
The Queensland Guide to Temporary Traffic Management, Transport for NSW TCAWS Technical Manual and the Victorian Code of Practice may all modify or replace AGTTM requirements.
Local authority supplements may also apply.
Designers should always check the relevant jurisdiction before finalising a design.
Summary: How AGTTM Helps TMDs Manage Excavation Delineation and Containment
AGTTM Part 3 provides TMDs with clear guidance on managing delineation around excavations.
The challenge lies in recognising when conditions shift into containment. Table 6.1 and jurisdictional supplements help make this distinction.
When the table or local requirements indicate a barrier system, escalation to a competent Traffic Engineer is the appropriate next step.
Need support with barrier selection or design?
Our team can assist with containment decisions, barrier layouts, and state-specific compliance requirements.
Contact Jarrod directly for all your barrier & construction traffic engineering needs: Jarrod.Lea@Moduseng.com.au
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