This is a follow-up question for "Ambiguous speed limit after passing a T-junction" (59728). The original question asks what the speed limit is, in the 20 metres after the intersection and before the 60-sign. This question asks whether ignorance of this speed limit is a valid defence.

We again consider the intersection between Fitzgerald St and Angove St in North Perth, Western Australia (left-hand traffic). This is a T-junction, with Fitzgerald St being the continuing road and Angove St being the terminating road.

Diagram of speed limit regions near the intersection

Dale M's answer to the original question establishes that:

  • The speed limit along Fitzgerald St northbound is 40 km/h (pink), beginning at the 40-sign before the intersection, all the way up to the 60-sign erected 20 metres after the intersection. Only after this 60-sign does the speed limit become 60 km/h (green).
  • The existence of a side road with a 50 km/h limit (blue) is irrelevant.

Now suppose that Bob approaches on Angove St and turns left into Fitzgerald St northbound. Bob knows nothing about the earlier 40-sign, but sees only the 60-sign, and concludes either:

  1. The speed limit on Fitzgerald St is immediately 60 km/h, since the 60-sign is consistent with all of Fitzgerald St being a 60-zone (which was indeed the case before 2016); or
  2. The speed limit on Fitzgerald St is immediately 50 km/h, since the 20 metres up to the 60-sign is an unsigned portion of a built-up area.

Bob turning left from Angove St onto Fitzgerald St northbound; Alice travelling on Fitzgerald St northbound straight through the intersection.

Therefore, after completing the left turn, Bob drives through the final 20 metres of the 40-zone believing that it is either a 60-zone or a 50-zone. (Yes this is difficult, but I think just doable with a powerful car by starting with a wide left turn into right lane at 35 km/h.)

Does Bob have a valid defence if issued with a speeding infringement?

If yes, suppose that Alice drives along Fitzgerald St northbound, straight through the intersection, clocking a speed of 60 km/h within the final 20 metres of the 40-zone.

Would infringing Alice require proving that she did not turn left from Angove St like Bob did?

  • @Trish That is the original question; Dale M said the "does Bob have a defence" part merits a separate question.
    – yawnoc
    Commented Jan 3, 2021 at 17:03
  • 1
    note that from a physics standpoint, unless Bob uses a race car, speeding the corner so he can get around the corner with 50 is close to impossible without hitting the sidewalks...
    – Trish
    Commented Jan 3, 2021 at 17:05

1 Answer 1


Bob has no defense

Speeding in , as it is throughout , is a strict liability offense. That means that intention to or knowledge that you are breaking the law is not required. Don’t know the limit? Doesn’t matter, you are still legally obliged to comply.

However, all the way up the chain, from the police officer, through the administrative arm to the judge, each person has discretion to waive the infringement notice. Basically, they can do that if they don’t think it’s “fair” on Bob in the circumstances.

Given that Bob managed to reach 40+km/h within 20m of a more than 90 degree corner I think the infringement notice is very fair. Negligent Driving is possibly the more appropriate offense.

However, it’s possible to imagine circumstances where waiving the infringement notice is fair. For example, if a speed limit sign has been removed or completely obscured by foliage or a parked vehicle and Bob could show he was not familiar with the area.

The question on Alice is, from above, moot.


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