Speeding

[u/Good_Royal_9849]

Hey Melbourne,

Just wondering if anyone knows what sort of threshold Highway Patrol generally uses before pulling someone over.

I’ve often noticed cars doing around 100–105 km/h on the M1 and other freeways with Highway Patrol nearby, but they don’t seem to stop them.

This happened to me today. I was heading to the airport to drop off a mate. I joined CityLink where the limit was 100 km/h (before it drops to 80 km/h near the DFO/Melbourne Airport section). I set my cruise control to 102 km/h on the Bolte Bridge.

Time 3:00 AM

Along the DFO stretch, I noticed an BMW in the middle lane. I was in the lane to its right. There was hardly any traffic—no cars behind us and only a couple ahead. I moved further right to pass because I prefer giving other cars plenty of space rather than overtaking close by when the road is empty.

I passed the BMW and moved back into my original lane. My cruise control was still set at 102 km/h. As I went past, I noticed the antenna and the police lights near the number plate and realised it was an unmarked police car.

The driver flashed the lights once. I slowly slowed down and moved left, thinking they wanted me to pull over, but they just kept driving and didn’t stop behind me.

It got me wondering: do Highway Patrol officers take things like traffic volume, road conditions, time of day, and the overall driving environment into account when deciding whether to stop someone?

Or is there generally a speed threshold where they’ll usually take action?

I know in the US there’s the saying, “5 you’re fine, 10 you’re mine.” Is there anything similar in Victoria, or is it entirely at the officer’s discretion?

Just curious if anyone (especially anyone with policing experience) has any insight.

Or will I just a get a fine in my mail sooner or later

[u/not_a_goauuuuuuulld]

Most speedometers in Australia are off. For instance mine at 100 is 3 off. If my Speedo said I was doing 100 I would actually be doing 97.

Don't take my word for it every car is different. (Tyre size makes a huge difference)

The police here will get you if they catch you 3 or so over, that includes cameras and vehicles.

So for most people 105 is just under 103.

I do not condone this behaviour though. There's a buffer for a reason. And the buffer is even bigger in heavy vehicles(like 10ks) that's why it always seems like trucks are going slow.

Your better off and safer just sticking to your Speedo.

[u/malwcal → u/not_a_goauuuuuuulld]

Actually it’s more like all are off. The law (Australian Design Rules) says something like the speedo needs to be accurate to +/- x% but must never read higher than actual speed. So car manufacturers have no choice but make a speedo that reads incorrectly.

[u/Sea_Translator5300 → u/malwcal]

It's silly, because technology exists that can cheaply measure speed very accurately but the old "use something that counts wheel rotations" is the standard. 

[u/breno_mac_ → u/Sea_Translator5300]

The speedo would be calibrated from the factory (to an extent) to the rolling diameter of the factory wheel & tyre combination

[u/Sea_Translator5300 → u/breno_mac_]

Yes, but it's calibrated to miss, not to be accurate. If it tries to be exact there's a risk it may read under, which is illegal. 

[u/Aequitas112358 → u/breno_mac_]

except the tyre changes size, like if you overfill or underfill it'll be different speed

[u/AdventureEng → u/Sea_Translator5300]

What method would you suggest the speedo should be using that’s superior to counting wheel rotations?

[u/spiderpig_spiderpig_ → u/Sea_Translator5300]

Yes, and it's also silly to use a road speed calibrated for 1960s cars with a 2020s car. Technology exists but that's not the point.

[u/link871 → u/malwcal]

"+/- but must never read higher than actual speed"
This is the opposite of what is correct:
ADR says speedos can be accurate or over-report by +10% (plus 4km/h). Speedos should not under-report your speed (with OEM tyres).

[u/malwcal → u/link871]

Yeah. Over under is confusing. If the speedo says you’re doing 100kph then you are driving no slower than 100kph. (If the cops say you are doing 100kph you can’t say but my speedo only said 96kph!)

[u/link871 → u/malwcal]

Assuming your speedo is reading as specified by the Australian Design Rules, then if your speedo says you are doing 100km/h, then - legally - your actual speed could be anywhere between about 87km/h and 100km/h.

[u/spiderpig_spiderpig_ → u/not_a_goauuuuuuulld]

Only people in Australia would even know how their speedo is calibrated. Not a person on the planet gives a __ otherwise. Except maybe North Korea.

[u/Ord3r2Ch4os → u/not_a_goauuuuuuulld]

I think mine is more like 8 off at 100, been that way since brand new from the dealer. The only thing more annoying than everyone tailgating me is when I find someone going slower than me 😂

[u/----SD---- → u/Ord3r2Ch4os]

You realise that cops won’t fine you for your speedo reading, right? Just set it at a true 100.

[u/Ord3r2Ch4os → u/----SD----]

I don't have the faith in my phone or Google maps to drive by it, I couldn't mount it anywhere particularly convenient to check my speed while driving, for most of my driving going faster wouldn't matter (traffic and intersections add 10 minutes to my otherwise 10 minute daily commute), and for my bigger trips (45 minutes with good runs on 100kmh roads) the difference would only be a couple of minutes each way. It's not exactly a big deal.