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How
do we stop our roads from freezing during the winter months? It
seems like a straightforward question and the answer would appear
to be just as obvious - throw salt on the roads.
In
the early 1980s it was found to be possible to measure the temperature
of the roads by using sensors. Soon computer models of the road
surface were developed. |
| Richard
Angwin |
But
how do we know that the roads are going to freeze? Which roads will
freeze first? Just how icy will the roads get?
These
are just some of the questions that the Met Office tries to answer
using its 'Open Road' system of monitoring and predicting the state
of the roads across the West Country.
Cold
nights
Twenty-five
years ago there was no such system in place. When weather forecasters
were predicting a cold night, gritters would go out and cover the
region's roads in a layer of salt.
Unfortunately
a cold night does not always result in icy roads so a great deal
of expensive and environmentally damaging salt was wasted, to say
nothing of the staff costs.
In
the early 1980s it was found to be possible to measure the temperature
of the roads by using sensors. Soon computer models of the road
surface were developed.
Forecasting
By
correctly forecasting the likely cloud, winds, air temperatures
etc. and entering this data into the model, the fist accurate predictions
of how the temperature of the road would change through the day
were produced.
Today
these models are sophisticated enough to tell exactly when the roads
are likely to freeze, how much ice will form and when any ice is
likely to melt.
Data
sensitive!
We
monitor the road temperatures at more than 700 sites around the
country. Data from these sensors is sent to forecasting centres
around the country who use this data to produce the forecasts for
our region.
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| Weather
conditions can make effective salting of the roads very difficult |
The
forecasts are sent to companies who are contracted to the Highways
Agency, such as W.S. Atkins on the A46 near the M4, and whose job
it is to send the gritters out when the roads are forecast to turn
icy or when snow is expected to fall.
To stop ice forming they use pure salt (not grit) which comes from
Cheshire or sometimes Northern Ireland. Spreading this on the road
surface lowers the freezing point of any water on the road surface,
preventing it turning into ice. Hundreds of tons of salt are used
during each 'season'.
Ninety
per cent accurate
We
aim for something like 90 per cent accuracy using this system. It's
not foolproof and even when we get the forecast 100 per cent right
the weather condition can make effective salting of the roads very
difficult.
by
Richard Angwin
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