Speed limit when overtaking? Teach me please.

Forums › Transport (cars, bikes and boats) › Speed limit when overtaking? Teach me please.

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#1163628 28-Oct-2014 15:20

ckc:
Inphinity:
Kyanar: no NZ road has the characteristics to get above 110Km/h.

Not quite true if you're talking just about the road surface (length, width, surface type, gradient etc), there are number of areas of roading in NZ which are suitable on paper for 120 -130km/h traffic, but at present there is no allowance for that under NZ speed regulations, and also, once driver competency, crash history, etc is taken into account, making it over 110 could be a bit risky. We need to get the idiots off the road first ;)

The fact that someone felt the need to start this thread makes me despair of driver education in NZ.

This thread, and driving in NZ every day. Both of those things make me despair of driver education NZ.

Also that some policeman don't seem to know the road rules or just actively ignore them.

Many things make me despair of driver education in NZ.

until you make compulsory pulling over of slower drivers this problem will continue to exist. or 2 laned per direction roads blanket rule in A roads (AND make people drive on left when no passing)

lagbort

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#1163630 28-Oct-2014 15:23

joker97:
Inphinity:
1) it's not the length of a truck, though, it's the distance the truck covers in the time it takes you to pass.
2) Anything that's unstable below 160kmh in good conditions should be in the same boat as a moped and not allowed in high speed areas, imo.
3) I'm also surprised at this, 160 - 190 on public roads is ridiculous imo. 130+ is just asking for trouble, imo. I would like to see 110 limits in some places, though.

i'm going to be really generous and say it takes 10s to pass a truck. not many cars can get to 90-190 in 10s.

i'm thinking about the undrivable bit ... who knows i don't drive such cars anymore thankfully (i'm thinking of my cars when i was a student in AKL ... )

Based on Truck and 90 kph, 2 sec separation beforehand, 10 metre clearance at end, allowing for oncoming traffic at 100kph + 10% clearance of that:
90 kph = 90,000/3600 = 25 metres/sec.
100 kph = 100,000/3600 = 27.8 metres/sec

Distance to pass = (2 x 25) + (Length of Truck) + 10 + (Length of Car) Say car is 5 metres, truck is 20 metres, then

Relative distance to pass = 50 + 20 + 10 + 5 = 85 metres

Time to pass = 85 metres / 2.8 metres/sec = 30.4 seconds Distance travelled to pass = 27.8 * 30.4 = 844 metres Clear distance required to oncoming traffic = (844 x 2) (+ 10%) = 1688 x 1.1

= 1,856 metres = 1.9 kilometres.

Batman

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#1163641 28-Oct-2014 15:32

huh?

lagbort

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#1163643 28-Oct-2014 15:33

you said being generous it would take 10s to pass a truck, the math shows that if both are doing legal speed it actually takes 30s and almost 2km

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#1163644 28-Oct-2014 15:36

ok oh thanks :D

but we were talking about someone overtaking a truck at 190kph and i tried to say it wasn't possible for most cars

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#1163646 28-Oct-2014 15:37

lagbort: you said being generous it would take 10s to pass a truck, the math shows that if both are doing legal speed it actually takes 30s and almost 2km

although there was someone who did suggest you pass a truck at 100, I argued that it was definitely impossible, and now you've showed why

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#1163650 28-Oct-2014 15:40

joker97: ok oh thanks :D

but we were talking about someone overtaking a truck at 190kph and i tried to say it wasn't possible for most cars

Given 30s though I would say there would actually be quite a few cars on the road that could get to 190ish

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#1163671 28-Oct-2014 15:53

going 30s between 90-190kph you can't overtake. either you run out of straight road so you end up in the ravine, but most importantly, the poster said he needed to go 190 because cars are coming, so i take that as within 10s, not easy to pull to 190.

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#1163673 28-Oct-2014 15:57

lagbort:

Based on Truck and 90 kph, 2 sec separation beforehand, 10 metre clearance at end, allowing for oncoming traffic at 100kph + 10% clearance of that:
90 kph = 90,000/3600 = 25 metres/sec.
100 kph = 100,000/3600 = 27.8 metres/sec

Distance to pass = (2 x 25) + (Length of Truck) + 10 + (Length of Car) Say car is 5 metres, truck is 20 metres, then

Relative distance to pass = 50 + 20 + 10 + 5 = 85 metres

Time to pass = 85 metres / 2.8 metres/sec = 30.4 seconds Distance travelled to pass = 27.8 * 30.4 = 844 metres Clear distance required to oncoming traffic = (844 x 2) (+ 10%) = 1688 x 1.1

= 1,856 metres = 1.9 kilometres.

If the car is traveling at 110km/h and all else is equal, it takes half the time (15.5 seconds) and 1.05km of clear road.

However if the truck slowed to 80km/h, and the car still overtakes at only 100km/h, it still takes 15.5s but you need only 900m clear.

Amazing what a huge difference that 10km/h makes in each case, really. And comparing the 90/100 scenario to the 90/110 scenario, which is safer? How often do you have 2km of clear, visible space?

DravidDavid

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#1163683 28-Oct-2014 16:07

ubergeeknz: How often do you have 2km of clear, visible space?

Not very often. Which is why when you get a stack of cars trying to pass a truck on a standard passing lane, the truck often slows down to a crawl to let everyone pass. Many of these passing lanes are up hill and the truck has no choice of course.

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#1163691 28-Oct-2014 16:12

ubergeeknz: ....How often do you have 2km of clear, visible space?

"Visible" is the key word. No-one can see if the road is clear 2km ahead, especially if you like to look for side-road traffic. You simply can't safely pass a vehicle doing 90km/h unless you break the law.

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#1163694 28-Oct-2014 16:14

lagbort:
joker97:
lagbort:
frankv:
DravidDavid:
clevedon:
Kyanar: and no NZ road has the characteristics to get above 110Km/h.

I'd have to disagree with that.

Indeed.

Your car, tyres, suspension and braking ability are much bigger factors. In certain cars 180 on these roads is suicide. In others, not so much.

I can't imagine a NZ road where 180 would be safe in a normal, street-legal road-going car. Maybe in a fully rollcaged, 5-point harnessed race car of some sort.

But that begs the question of what happens to the normal road-going car you run into. In any car, 180 on these roads is murder.

The entire Wellington Motorway from the city to either Porirua or Upper Hutt would be fine at 180 in any decently new car or well maintained sports car

until you lose concentration and rear end someone because you didn't realise them going at 80 means you'd catch their bum very fast

or the one going at 80 suddenly decides to come into your lane and not realising you were approaching them twice as fast

or until you do a Paul Walker's mate

I did mean of course without other traffic, or in traffic doing similar speeds. The road is perfectly capable of such speeds, current traffic is not

Hmmm... how do you ensure that there's no other traffic? You would have to close every side road and gateway.

Of course, you also meant that the traffic lights wouldn't be an issue. And that your tyres would be appropriate for the weather. And that your car would have sufficient downforce to not get airborne at the Korokoro lights, or good enough springs to absorb the landing. I guess that excludes most decently new cars and well maintained sports cars. I do believe I'd pay good money to see someone go 180kph around the (I believe 55kph? it has been a while) corner under the Petone overbridge.

So I think we're in agreement... the only place for 180kph in NZ is on a track or closed road.

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#1163698 28-Oct-2014 16:18

I was in a car that went around the Petone Overbridge corner at 120kmh, I was not driving but nearly had an incident I haven't had since probably 2 years old

lagbort

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#1163701 28-Oct-2014 16:20

KiwiNZ: I was in a car that went around the Petone Overbridge corner at 120kmh, I was not driving but nearly had an incident I haven't had since probably 2 years old

I quite frequently do 110-120 around the Petone overbridge corner... It's not even close to dangerous for a corner of that radius, I'm more concerned about who is on the other side than the corner itself

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#1163702 28-Oct-2014 16:23

lagbort:
KiwiNZ: I was in a car that went around the Petone Overbridge corner at 120kmh, I was not driving but nearly had an incident I haven't had since probably 2 years old

I quite frequently do 110-120 around the Petone overbridge corner... It's not even close to dangerous for a corner of that radius, I'm more concerned about who is on the other side than the corner itself

I should have mentioned it was in an Audi Q7. It was very scary.

I take that corner at about 70 due to cyclists etc

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