weather station contains a number
of sensors that combine to calculate
the level of grip on the road surface.
Weinberger says: “The station has
non-invasive sensors that point down
at the roadway and pick up the
temperature and condition. The other
thing we look at is what is the current
weather. So is it actively snowing or
raining? We put all those factors
together and output a grip
coefficient, with 0.8 being a
completely dry, high-grip surface.”
The station uses lasers to detect
the moisture level in the road surface.
“It sends out a beam and
depending upon the
reflection, it can understand
whether the water molecules
on the roadway are
crystalline or liquid. So
whether it’s ice, snow or
water,” he says
In the case of ice the
signal that is bounced back also helps
the system calculate the amount of
air inside the ice. This is an important
measurement because it helps
determine the type of ice on the road.
“The difference between white ice
and black ice is due to the amount of
air that’s in there – when air gets in
to ice it turns it white,” he says.
Some of the practical applications
of Vaisala’s weather sensing
technology are fairly intuitive, says
Weinberger. For example, Colorado
Department of Transportation is
looking at using the technology for
1996 The year AASHTO, ITE
and NEMA agreed to work
together to develop and
maintain NTCIP standards
for ITS interoperability
|Weather Responsive Intersections
The station has non-invasive
sensors that point down at
the roadway and pick up the temperature
and condition
Jason Weinberger, Vaisala
when to enact their chain laws –
driving restrictions imposed during
icy weather that make it mandatory for
commercial vehicles in mountainous
areas to drive with tire chains.
Other applications of the technology
are less obvious. In Arizona, for
example, the same sensors that
produce the grip coefficient are used to
detect the presence of dust storms.
“So when the visibility drops
they’re able to reduce the speed limit
on a corridor using variable speed
limit signs,” says Weinberger.
Traffic management
Another important aspect of weather
responsiveness is the data transfer
between the sensors and traffic
managers. To facilitate this transfer
Vaisala’s road weather stations in the
US are compliant with the National
Transportation Communications for
Intelligent Transportation System
Protocol (NTCIP), a family of
standards that allows communication
between electronic traffic control
equipment from different
manufacturers.
“So NTCIP-compliant software
can poll our weather station to get
that grip data and then utilize it,”
says Weinberger. “Vaisala itself has
software that has that same polling
capability. In that scenario, we could
do a direct data transfer to the
systems there control the traffic
signals, for example.”
The interoperability made possible
by the NTCIP standards – which
were initiated in the mid-1990s – is
the reason automated systems like
ASC can exist. But while the high cost
of ASC currently makes automation
quite niche, replacing fibre optics
with wireless connectivity would
likely bring down the cost.
According to Fu developments
like this are in the offing with some
companies already experimenting
with “using wireless technology to
connect the traffic signal controller to
the traffic control centre.”
Until that happens the work
done by Fu and his colleagues is an
important interim step, offering traffic
managers a low cost way of making
their traffic signalling weather
responsive and the roads they
manage safer as a consequence.
Top left: A RWIS
(roadside weather
information system)
installed by Vaisala in
Pennsylvania
PHOTOGRAPHS: DANIIL, AKARAT PHASURA/STOCK.ADOBE.COM
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November/December 2019 Traffic Technology International
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