Portable Traffic Signals: When, Why, and How to Use Them Under AGTTM

Introduction

Portable traffic signals are a valuable tool in Temporary Traffic Management (TTM) — often safer and more consistent than human controllers.

Under AGTTM, their use must be risk-justified, planned with precision, and clearly documented in the TMP.

When to Use Portable Signals

Portable signals should be considered when:

• Traffic flows need to alternate through a single lane

• Entry/exit timing can be managed predictably

• Sight distance is adequate in both directions

• Manual control is unsafe, impractical, or resource-intensive

They are especially useful in:

• Shuttle flow arrangements

• Night works

• Rural or regional sites with limited personnel

Reference: AGTTM03-21, Section 5.10.1; QGTTM Part 7, Section 4.4

Advantages Over Traffic Controllers

• Reduced risk to personnel

• More consistent gap and timing control

• Less fatigue-sensitive than humans

• Easier compliance with road authority conditions

Portable signals are not a replacement for planning — but they are a smarter option when used appropriately.

Key Design Considerations

When using portable traffic signals:

• Include signal location and timing in the TMP

• Ensure they comply with AS 4191 standards

• Provide adequate advance warning and VMS

• Place them where they are visible, stable, and protected

If a worksite involves complex geometry (e.g. curve, crest, intersection), risk assessment must clearly justify use.

Reference: AGTTM02-21, Section 3.3.5; AGTTM03-21, Section 5.10.2

Signal Timing Guidance

AGTTM recommends signal cycles be calculated based on:

• Queue clearing time

• Entry/exit distance

• Road gradient and surface condition

Cycle times should be reviewed regularly during the shift.

Common Pitfalls

• Using signals in poor visibility without lookout or VMS

• Failing to coordinate with third-party signals (e.g. rail, pedestrian crossings)

• Not updating timing after traffic pattern changes

• Installing signals without documenting control logic

Real-World Tip

When replacing a traffic controller with portable signals, document that clearly in your TMP and Risk Assessment. Include a contingency plan in case of power loss or device failure.

Also ensure field staff are trained in safe placement and remote override.

What Auditors Expect

• Signal use risk-justified and approved

• TMP includes timing, location, and contingency

• Physical setup aligns with AGTTM diagrams

Well-documented portable signal plans often result in faster approval and fewer mid-job issues.

Final Word

Portable traffic signals bridge the gap between human control and full automation. They are precise, protective, and compliant — when used as part of a planned, documented TMP.

Don’t treat them as a plug-and-play option. Treat them like any engineered control: deliberate, accountable, and built into the risk story.