Damage from debris in road

Joe_Horner

Ultrasonic wrote: »

I'm clearly missing something :huh:

victor2 wrote: »

You're not the only one.

Don't panic!

robatwork

http://en.wikipedia.org/wiki/Towel#Appearances_in_popular_culture

should lead you on an enlightening journey

Nearly_Old

john342 wrote: »

It may of been possible to stop just in time, although it is not certain. In any case, where do you draw the line at what size obstacle are you expected to be able to see? Should I drive everywhere at 5mph just in case there is a nail in the road?

If the road in question conforms to the requirements of the DMRB (Design Manual for Roads and Bridges) then the visibility requirements for Stopping Sight Distance are:

Driver's Eye Height: 1.05m to 2.00m
Object Height: 0.26m to 2.00m

For a Design Speed of 48kph/30mph the Desirable Minimum Stopping Sight Distance is 70m and if the One Step Reduction is used then this reduces to a Stopping Sight Distance of 50m.

No you wouldn't be able to see a nail but IF the road generally conforms to the design standards an object standing >200mm above the road surface should be visible within a distance that allows a vehicle to stop.

vaio

so anything less than 260mm (like the 150mm rock in question) is not going to be visible until you are too close to stop?

Iceweasel

So we really need to know the make and model of car - so we can find out the ground clearance.

The rock must be assumed to be a 20 to 30 mm bigger than that to have caused that much damage.

Joe_Horner

vaio wrote: »

so anything less than 260mm (like the 150mm rock in question) is not going to be visible until you are too close to stop?

Not quite, because that spec is for the design speed of the road - in this case 30mph.

So, if the driver was travelling at the speed limit, regardless of the conditions then you'd be right. If the driver had slowed to an appropriate speed for passing a lorry in busy traffic then the visibility distance for the rock in question would be the same, but the stopping distance would be less.

Nearly_Old

vaio wrote: »

so anything less than 260mm (like the 150mm rock in question) is not going to be visible until you are too close to stop?

Not an easy question to give a definitive answer to as there are so many variables. When designing new roads or improvements to existing roads sight lines are someting that usually requires a lot of attention to detail so trying to keep it short:

The road surface is basically a flat plain surface that can be level or on a longnitudinal gradient and can also be cambered (high in the middle falling down to each side) or superelevated (falling either towards the nearside or offside). In urban areas there can be street signs, guardrails, etc and in rural areas trees, bushes, etc.

On the plus side an object on the road surface becomes an irregularity on the flat plain surface and our eyes are generally better at noticing irregularities. The colour / shape of the object can also make a difference.

An example is speed bumps: the maximum allowable height is 100mm but generally heights between 65 and 85mm are used. There is a straight section of road that I use with black tarmac speed bumps on the black road surface and these are easily visible from around 100m. There is one however just around a tight righthand bend which, if there is oncoming traffic blocking the sight line across the inside of the bend isn't visible until you are about 25m away from it.

bigjl

Was going to read the entire thread but it seems a bit messy.

None of us was there so we don't know exsctly what happened.

I hit some debris on the M25 a couple of weeks ago.

Bit of square shaped metal fell off the side of a polish lorry in the lane ahead of me and bounced down the road.

Couldn't swerve much as traffic all around and the wife was following behind.

Managed to lose some speed and hit it when it was as low to the ground as possible then went over it with both o/s wheels so it didn't bounce up and hit the wifes windscreen. But i still nicked the front bumper low down.

Now will somebody say i could have avoided it completely?

Well yes i could but caused a probable fatal rtc in doing so.

It is possible the OP was distraced by the workmen and large vehicle parked on the side and their attention was partially diverted.

I don't think the OP will get any financial recompence but i wish them luck.

And looking on the bright side they weren't injured physically.

bigjl

Just had a thought part of the permissions to carry out the work should include keeping the road clear and clean during the works.

So i would suspect they have a duty of care to any road user that hits something they have left there.

As such, surely the road should have been closed whilst this was done.

AdrianC

bigjl wrote: »

I hit some debris on the M25 a couple of weeks ago.

Bit of square shaped metal fell off the side of a polish lorry in the lane ahead of me and bounced down the road.

Couldn't swerve much as traffic all around and the wife was following behind.

Managed to lose some speed and hit it when it was as low to the ground as possible then went over it with both o/s wheels so it didn't bounce up and hit the wifes windscreen. But i still nicked the front bumper low down.

Now will somebody say i could have avoided it completely?

So - just to compare the two situations...

- Stationary obstacle, high enough to hit bottom of engine hard, urban 30mph limit, already slowed to squeeze between stationary truck and oncoming traffic

- Moving obstacle, low enough to barely nick front valance, 70mph motorway limit, free moving traffic.

Yet _still_ you saw it in plenty of time to brake, slow and position yourself to minimise damage.