Motorway aquaplaning - an avoidable accident?

[DonkeyApple]

rlg43p said:

I'm out. There's so much st being expressed by people who clearly don't really understand the issues.

There's fk all car control you can exercise if you're aquaplaning - you just need to drive appropriately to the conditions.

The car control required is to basically chill out and not do anything while prepping for when grip returns. In reality, that suggests that the average driver who is oblivious to what to do or what is happening is likely to have the right response by default.

As you say, the real killer secret is to be able to tell whether you're driving a van or a mid engined sports car and then to know whether it's wet or dry outside that vehicle. Those two bits of data can then be used to ascertain basic odds on whether driving inappropriately is more or less likely to ruin your day on that occasion.

A very crude rule of thumb for mid engines sports car drivers when there is standing water about is that if you're not being passed by van and SUV drivers then you're probably not driving appropriately.

[Countdown]

rlg43p said:

Lexington59 said:

Passive aggressive?

The dude has trashed two Boxsters. Some may say that's unlucky but I'm not sure he has much to lose from a bit of tuition on car control...

I'm out. There's so much st being expressed by people who clearly don't really understand the issues.

There's fk all car control you can exercise if you're aquaplaning - you just need to drive appropriately to the conditions.

Surely those people who "understand the issues" would be able to avoid aquaplaning in the first place?

Speed isn't the only factor but it IS a big factor. Mid-engined/rear-engined cars are also going to behave differently but if that is something that causes the driver to aquaplane it's a lack of driver capability/understanding/experience of how their car behaves.

I'm sure this thread will run for volumes. however the sad fact is that few people are prepared to recognise their own errors when the S hits the fan

[millen]

Does switching on the hazard lights if trundling along a wet motorway at 30 mph make sense, or is that frowned upon? Might avert the risk of someone with less caution rear-ending you from 60 mph.

Also, how are police drivers taught to recognise the aquaplaning risk? It's some years since I've been in such a situation but I do recall loud sloshing noises from waves of water hitting the floor being a warning to back off.

[DonkeyApple]

millen said:

Does switching on the hazard lights if trundling along a wet motorway at 30 mph make sense, or is that frowned upon? Might avert the risk of someone with less caution rear-ending you from 60 mph.

Also, how are police drivers taught to recognise the aquaplaning risk? It's some years since I've been in such a situation but I do recall loud sloshing noises from waves of water hitting the floor being a warning to back off.

Your problem with some cars is that the speed which is safe in terms of maintaining control during such events is going to break the threshold where the speed is too slow to be safe. Ie, much below 50 and you're starting to ask to be punted from behind.

Rear dogs are the first thing to go on to help with visibility if you're having to move into L'1 and travel slowly but that's also the point at which you need to start considering just leaving the motorway when in a car that is just more susceptible to standing water than typical traffic.

[TheJimi]

Took me a ridiculous amount of time to work out "rear dogs" = rear fogs

[Koolkat969]

No aquaplaning here but a few stalled cars.

I guess they weren't going fast enough to aquaplane but fast enough to hit the water hard and stall!

https://youtu.be/fPSiUx851Qo

[SidewaysSi]

Everyone should drove something like a Caterham when it is pissing down with rain as that sort of car teaches you to drive. And if you get it wrong, it will hurt or you will die.

All these people driving their new tin boxes with all the systems on think they are good. Until they suddenly reakise that they aren't.

[MC Bodge]

SidewaysSi said:

Everyone should drove something like a Caterham when it is pissing down with rain as that sort of car teaches you to drive. And if you get it wrong, it will hurt or you will die.

All these people driving their new tin boxes with all the systems on think they are good. Until they suddenly reakise that they aren't.

Or a motorbike

[DonkeyApple]

TheJimi said:

Took me a ridiculous amount of time to work out "rear dogs" = rear fogs

A Labrador gaffer taped to the back would soften a blow from an HGV though!

[jamieduff1981]

This was derived empirically by NASA long agp for aviation rather than for cars, and it's very simplified ignoring the effects of many variables.


[i]The contact pressure between tire tread and pavement establishes the escape velocity of bulk water drainage from beneath the tire footprint. High pressure tires can expel surface water more readily from the footprint than low pressure tires. When the aircraft ground speed equals or exceeds the escape velocity of water drainage from the footprint, choked water flow occurs. The tire has now reached a state of total dynamic hydroplaning. Test results .... indicate that the critical aircraft groundspeeds required for this total hydroplaning condition to occur on a flooded (runway water depth is greater than tire tread groove depth) pavements with an unbraked tire are approximately:

Spin-down (rotating tire) speed, knots = 9 sqrt Infl. pressure, psi
Spin-up ( nonrotating tire) speed, knots = 7.7 sqrt Infl. pressure, psi

......... It is important that pilots be aware that the lower hydroplaning spin-up speed, rather than the high hydroplaning spin-down speed, represents the actual tire situation for touchdown on flooded runways.[/i]


For cars, this tends to give speeds a bit higher than those at which people have experienced aquaplaning, but the relationship of aquaplaning speed with tyre pressure does describe in a crude way the relationship of tyre contact patch with the mass of the vehicle.

[trails]

SidewaysSi said:

Everyone should drove something like a Caterham when it is pissing down with rain as that sort of car teaches you to drive. And if you get it wrong, it will hurt or you will die.

All these people driving their new tin boxes with all the systems on think they are good. Until they suddenly reakise that they aren't.

In spades. I remember driving my S2000 home after buying it; torrential rain, Lane 1 M25 whilst being overtaken by trucks. Those moments never leave you do they

[Mave]

jamieduff1981 said:

This was derived empirically by NASA long agp for aviation rather than for cars, and it's very simplified ignoring the effects of many variables.


[i]The contact pressure between tire tread and pavement establishes the escape velocity of bulk water drainage from beneath the tire footprint. High pressure tires can expel surface water more readily from the footprint than low pressure tires. When the aircraft ground speed equals or exceeds the escape velocity of water drainage from the footprint, choked water flow occurs. The tire has now reached a state of total dynamic hydroplaning. Test results .... indicate that the critical aircraft groundspeeds required for this total hydroplaning condition to occur on a flooded (runway water depth is greater than tire tread groove depth) pavements with an unbraked tire are approximately:

Spin-down (rotating tire) speed, knots = 9 sqrt Infl. pressure, psi
Spin-up ( nonrotating tire) speed, knots = 7.7 sqrt Infl. pressure, psi

......... It is important that pilots be aware that the lower hydroplaning spin-up speed, rather than the high hydroplaning spin-down speed, represents the actual tire situation for touchdown on flooded runways.[/i]


For cars, this tends to give speeds a bit higher than those at which people have experienced aquaplaning, but the relationship of aquaplaning speed with tyre pressure does describe in a crude way the relationship of tyre contact patch with the mass of the vehicle.

It would be interesting to know which factors they varied, and which they kept constant. I'm struggling to correlates the NASA relationship with my personal experience of lots of different cars with different aquaplaning chatacteristics, but similar tyre pressures (I recall my RX7 was much more aquaplaney than the mk1 micra my wife had at the same time, but they were both ~30psi)

[DuncanM]

Mave said:

It would be interesting to know which factors they varied, and which they kept constant. I'm struggling to correlates the NASA relationship with my personal experience of lots of different cars with different aquaplaning chatacteristics, but similar tyre pressures (I recall my RX7 was much more aquaplaney than the mk1 micra my wife had at the same time, but they were both ~30psi)

FWD cars just hoof along fairly obliviously, because the dynamics are so much safer when the wheels re-grip, after the aquaplaning.

My GT86 was horrid in the heavy rain in December.

[LunarOne]

Mave said:

jamieduff1981 said:

This was derived empirically by NASA long agp for aviation rather than for cars, and it's very simplified ignoring the effects of many variables.


[i]The contact pressure between tire tread and pavement establishes the escape velocity of bulk water drainage from beneath the tire footprint. High pressure tires can expel surface water more readily from the footprint than low pressure tires. When the aircraft ground speed equals or exceeds the escape velocity of water drainage from the footprint, choked water flow occurs. The tire has now reached a state of total dynamic hydroplaning. Test results .... indicate that the critical aircraft groundspeeds required for this total hydroplaning condition to occur on a flooded (runway water depth is greater than tire tread groove depth) pavements with an unbraked tire are approximately:

Spin-down (rotating tire) speed, knots = 9 sqrt Infl. pressure, psi
Spin-up ( nonrotating tire) speed, knots = 7.7 sqrt Infl. pressure, psi

......... It is important that pilots be aware that the lower hydroplaning spin-up speed, rather than the high hydroplaning spin-down speed, represents the actual tire situation for touchdown on flooded runways.[/i]


For cars, this tends to give speeds a bit higher than those at which people have experienced aquaplaning, but the relationship of aquaplaning speed with tyre pressure does describe in a crude way the relationship of tyre contact patch with the mass of the vehicle.

It would be interesting to know which factors they varied, and which they kept constant. I'm struggling to correlates the NASA relationship with my personal experience of lots of different cars with different aquaplaning chatacteristics, but similar tyre pressures (I recall my RX7 was much more aquaplaney than the mk1 micra my wife had at the same time, but they were both ~30psi)

Cars are expected to grip strongly when lateral forces are applied during cornering, while aircraft tyres need to be able to slip sideways to a degree to prevent them grabbing during crosswind landings. In addition, aircraft tyres also need to be much more resistant to aquaplaning at high speeds because a typical airliner can't fly much slower than 145 kt (165mph) without falling out of the sky. Aircraft tyres have much higher loading factors than car tyres and they're round in cross section, quite different to modern low-profile car tyres which are flat. It's much easier for a given depth of water to lift a car tyre off the road surface than an aircraft tyre off the runway. So I'm not sure that NASA's research really apply to cars with totally different wheel loadings, speeds and tyre cross-sections.

I'm also not convinced that it's only when the depth of standing water exceeds the depth of the grooves and sipes in the tyre that there is a risk of aquaplaning. Considering the cross section of a car tyre in contact with the road, between 50% and 60% of that cross section will be rubber contacting with the road, with the other 40-50% being grooves and sipes which can be considered parts of the tyre where no contact takes place. If we assume for the sake of argument that the ratio of rubber to gap is 50:50, then a 3mm tread depth cannot adequately take up 3mm of standing water. It would only take 1.5mm of standing water to fill the 3mm voids in the tyre contact patch.

In actuality, this isn't correct because the rolling action of the tyre functions to pump water out from under the tyre, but there's a limit to the efficiency of this process and there will be a speed at which a tyre with 3mm tread depth cannot pump 3mm of standing water out from under the tyre. The ratio of rubber to void contacting the road, the deeper the tread depth, the design of the tread pattern, the loading on the tyre, the depth of the water and the speed at which the tyre moves through the water are all significant variables. But for a modern lightweight sports car wearing sporty tyres optimised for dry conditions (high rubber to void ratio), 3mm of tread depth is not nearly enough to disperse 3mm of standing water at motorway speeds.

[OzzyR1]

Just seen this thread and it reminded me of something that makes me cringe to this day.

Aged 17, I had a 3.0 Capri and was being a general tool and showing off to friends in an empty industrial estate car park late in the evening.

Not really having any experience of driving (much less car control - having passed my test only 2 months before), I misjudged my speed & braking ability and stuffed the front end of the car under a post and rail style fence at the edge of the car park. The rail was just the right height for the front of the Capri bonnet to slip under then crumple the whole bonnet and wings with the momentum.

Couldn't face telling my dad that I was being a tw*t and with the thought that it had been raining heavily that evening, my approach was to tell him I had aquaplaned and that would (in my mind) absolve me of blame.

Of course his first question was "how fast were you going when you aquaplaned then"?

Not having any understanding of aquaplaning & speed, but knowing I would get in trouble for driving fast, I responded "under 20mph".

His stare and shake of the head said it all. I didn't know at the time but looking back, as I said in the first line, cringe.

[carl_w]

Mave said:

It would be interesting to know which factors they varied, and which they kept constant. I'm struggling to correlates the NASA relationship with my personal experience of lots of different cars with different aquaplaning chatacteristics, but similar tyre pressures (I recall my RX7 was much more aquaplaney than the mk1 micra my wife had at the same time, but they were both ~30psi)

Space Shuttle landing speed was over 200mph...

[LunarOne]

carl_w said:

Mave said:

It would be interesting to know which factors they varied, and which they kept constant. I'm struggling to correlates the NASA relationship with my personal experience of lots of different cars with different aquaplaning chatacteristics, but similar tyre pressures (I recall my RX7 was much more aquaplaney than the mk1 micra my wife had at the same time, but they were both ~30psi)

Space Shuttle landing speed was over 200mph...

And the tyre pressure was either 300 or 340psi!

[TheJimi]

DonkeyApple said:

TheJimi said:

Took me a ridiculous amount of time to work out "rear dogs" = rear fogs

A Labrador gaffer taped to the back would soften a blow from an HGV though!

[carinaman]

legless said:

jjones said:

Often see cars way on the verge on the A46 as it exists Coventry to the south after aquaplaning. Heavy rain always leaves large patches of standing water in the outside lane. If you don't know (or don't care) it is a recipe for disaster.

I used to drive that section every day. You could tell the regular users of the road because if it was raining they'd stay well away from the outside lane until Kenilworth.

It's the worst section I've ever seen for standing water, and it's been like that for at least 20 years. It baffles me why the drainage hasn't been fixed in that time.

So when the authorities have their little maps with red marker pins showing where the accidents are to justify the siting of Speed Cameras why hasn't somebody noticed accidents happening on that stretch of road and that the accidents coincide with wet weather and thought 'Perhaps we need to look at improving the drainage'?

Speed kills.

I've really not done a lot of miles so far this year but on a not particularly wet day I was going up a hill in a 40mph limit and it was another case of seeing water coming across the road in front of me right to left where the gaps were in the white lines in the centre of the road. It's often like that on a NSL dual carriageway I use.

[carinaman]

legless said:

jjones said:

Often see cars way on the verge on the A46 as it exists Coventry to the south after aquaplaning. Heavy rain always leaves large patches of standing water in the outside lane. If you don't know (or don't care) it is a recipe for disaster.

I used to drive that section every day. You could tell the regular users of the road because if it was raining they'd stay well away from the outside lane until Kenilworth.

It's the worst section I've ever seen for standing water, and it's been like that for at least 20 years. It baffles me why the drainage hasn't been fixed in that time.

So when the authorities have their little maps with red marker pins showing where the accidents are to justify the siting of Speed Cameras why hasn't somebody noticed accidents happening on that stretch of road and that the accidents coincide with wet weather and thought 'Perhaps we need to look at improving the drainage'?

Speed kills.

I've really not done a lot of miles so far this year but on a not particularly wet day I was going up a hill in a 40mph limit and it was another case of seeing water coming across the road in front of me right to left where the gaps were in the white lines in the centre of the road. It's often like that on a NSL dual carriageway I use.

Edited by carinaman on Friday 14th January 00:52