[paul.fr]

There must be a speed at which road gritters get optimum coverage, does anyone know it? Also, "how far" does one load go?

[dentstudent]

by experience, the general speed is in the region of Mach 3 and the range is targetted onto my bonnet. And I don't mean my hat.

[Don_1]

by experience, the general speed is in the region of Mach 3 and the range is targetted onto my bonnet. And I don't mean my hat.

This may be the case on German roads, but on UK roads they move so fast they can't be seen, or is it that they just don't bother coming out?

[dentstudent]

Nein, ve grit ze strassen mit der airplanes, ja!

[Don_1]

Nein, in their dreams!!!

[graham.d]

It is not, directly, the speed of the gritter that causes high impact to passing vehicles. The grit is not ejected at high speed. The problem is in the speed of the passing vehicles hitting the bouncing bits of rock. Of course there is a good deal of correlation because once the grit hits the road it tends to stop having too much forward velocity, and if the gritter is going quite fast it means overtaking vehicles have to go faster to pass or spend longer being pummelled.

The driver of the gritter will judge the optimum speed so as to get back to the depot before his tea goes cold :-)

I found out from one UK council website that between 6 and 10 tons of rock salt are spread along 100 Km (65 miles) of road. Another site (Stoke on Trent) says "Spread rates depend on the weather conditions. In frost conditions we spread at a rate of 10 grams per square metre, in ice conditions we spread at 20 grams per square metre and when it snows we spread at 2 X 20 grams per square metre for up to 50mm of snow. Above this level ploughs are used."

Big gritters can carry 18 tons I believe. But because the effective time to spread is before the temperature drops below freezing, they usually are limited by a narrow time window - maybe about 2 hours. On a motorway (ie a very wide road) this would mean that a big gritter would not be using a full load unless snow was predicted, because his speed to deposit it in the time would be unreasonably high. I could not find out an optimum speed, but I suspect that the limitation is more to do with safety for overtaking vehicles than for getting a better distribution. I would guess a max speed of about 50km/hour would do the job.

A new design of gritter is being used where the salt is pre-wetted allowing more efficient use of the salt and (maybe) less damage to passing vehicles.

An interesting question.

[dentstudent]

Well, thinking about this area of Germany, I've not seen gritters at all. Generally, when it snows, the ploughs are needed, but also (and probably most significant) you are not allowed into certain areas unless you have winter tyres. These (as you might surmise) are deeply treaded tyres that can deal efficiently with snow and slush. This winer tyre theme is spreading, and generally, there is an increase in the number of people who are fitting these tyres every winter. If you look into many people's garages, there is a spare set of wheels which they change according to season. Perhaps the UK should adopt a similar strategy...

[lyner]

'Winter' tyres don't last very long on snow-free roads so, in the UK, we have a dilemma.