Barrier Systems in TTM: How to Design, Justify, and Apply Them Under AGTTM

Introduction

Temporary barrier systems are a key component of safe traffic management. But under AGTTM, barriers must be more than an afterthought or default option — they must be justified, planned, and installed with precision.

When Are Barriers Required?

Barriers should be considered when:

• Workers are exposed within 3 m of live traffic

• Vehicle intrusion risk is medium or high (based on risk assessment)

• The site involves excavation, drop-offs, or fixed hazards within the clear zone

Barriers may be:

• Rigid (e.g. concrete)

• Semi-rigid (e.g. steel)

• Flexible (e.g. wire rope or water-filled)

Reference: AGTTM03-21, Section 5.3.1; AGTTM08-25, Section 2.4.1

Design Requirements

All barriers must be:

• Approved and crash-tested (per AS/NZS 3845)

• Installed with adequate clearance for deflection

• Anchored or terminated correctly

• Included in the TMP with layout, length, and risk context

Important: Dynamic deflection must match site conditions. Don’t install flexible barriers with a 1 m clearance if the deflection is rated at 2.5 m.

Reference: AGTTM08-25, Section 3.3

Common Mistakes

• Placing barriers too close to hazards or workers

• Underestimating deflection clearance

• Omitting barrier design from the TMP

• Using barriers as pedestrian protection (not compliant)

Barriers protect from vehicle intrusion, not slips, trips, or footpath separation.

Real-World Tip

Use AGTTM Table 5.1 to determine lateral clearance from live lanes. Also refer to barrier manufacturer specs — they override assumptions.

Include buffer zones on both ends and avoid hard tapers into barrier lines.

What to Include in the TMP

• Barrier type and specification

• Deflection zone and lateral clearance

• Length of need and start/end points

• Risk justification (why the barrier is needed)

• Inspection and maintenance instructions

Reference: AGTTM03-21, Section 5.3; AGTTM02-21, Section 3.3.5

Auditable Criteria

Road authorities and auditors will check for:

• Barrier layout matches plan

• Deflection clear zone maintained

• Safe terminations or crash cushions

• Installation log and inspection record

A barrier is not a tick-box. It’s an engineered control with life-saving consequences.

Final Word

Temporary barriers are critical, but only when designed for the risk they’re controlling. Under AGTTM, they are subject to the same principles as any other engineered safety device: fit-for-purpose, auditable, and built into the TMP.

If the barrier is protecting workers, your plan must prove that — with the right clearance, the right device, and the right reason.