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image. Nevertheless, the radar
systems generated valid alarms.
Typical false alarm rates dur-
ing the course of the trial were
measured and found to be around
one for every 24-hour period. It
is hoped that these will be further
reduced during a planned rollout
of the system as processing algo-
rithms are improved and further
installation experience is gained.
Since the Clearway process-
ing system is able to track each
vehicle as it travels along a road,
during the course of the trial
Navtech's technical staff were able
to adapt the processing to suit
the client's requirements. For
example, peak-hour traffic queues
on the section of the E4, although
technically involving stopped
vehicles, and therefore incidents,
are not of interest to control room
operators dealing with emergency
response. They are only really of
interest for the purposes of general
management of the road network
and perhaps future planning. As
`incidents' they simply add to the
already long list of alarms that
operators have to deal with.
Processing business rules were
added that allowed the number of
vehicles below a threshold speed to
be counted. In the event that these
exceed a threshold in a defined
length of the carriageway, a queue
flag can be set (and later unset).
These alerts are made up of several
stopped or queuing vehicles, as is
usually the case in a traffic queue,
but do not require an immedi-
ate operator response as in an
emergency situation. Of course,
if a stopped vehicle is detected
outside of the queuing lane then
the incident will continue to be
detected. n
Navtech installed two TS350X
model radar systems. The
TS350X can detect a man-sized
object out to a radius of 350
metres. Since it can provide 360
degree coverage, each sensor can
therefore provide a total of 700
metres coverage where condi-
tions allow.
To limit costs and reduce
works by taking advantage of
nearby power and Ethernet con-
nections, the radar systems were
each installed on a post close to
an existing gantry. In addition,
a number of fixed cameras were
installed high on the gantries.
These were to provide video
images of detected incidents
for the purposes of testing and
evaluation.
The data from the radar
was communicated back to the
client's office where a processing
system was configured to gener-
ate incidents alarms including:
stopped vehicle; slow-moving
vehicle; pedestrian; reversing
vehicle; and lost cargo/debris
detection. These alarms were
subsequently used to trigger
recording on a local digital
video recorder. After an initial
configuration period the system
was left to run and detection
and false alarm rate perfor-
mance assessed.
Testing
Examples of typical detected
incidents were registered during
live traffic operations. In each
case the radar systems gener-
ated the alarm messages and
camera pictures were taken from
recorded video. In some cases
the weather conditions were too
poor for a good-quality video
the numbers of incidents and ac-
cidents. A solution was sought.
Many requirements
Trafikverket had a number of
requirements in addition to reli-
able detection irrespective of the
general weather conditions. It
needed to ensure that detection
was continually reliable, with little
or no routine maintenance. Full
lifecycle costs are an important
consideration when designing and
financing an incident detection
system and, as well as equipment
failure or malfunction, operat-
ing costs should also include the
nuisance cost of responding to
system-generated false alarms.
Trafikverket also required the
system to provide full-carriageway,
all-lane coverage from only a few
installed sensors, as the costs of
installing and providing power
and communications to a large
number of additional gantries
or mounting posts could not be
justified. Long-range detection
capabilities were essential.
Two trial locations
In early 2010, Trafikverket invited
UK company Navtech Radar to
demonstrate the capabilities of its
Clearway radar incident detection
system. Two trial locations in the
Stockholm area were chosen, one
above ground on the E4 and an-
other below ground in the Södra
Länken tunnel.
For the surface installation,
Trafikverket is responsible for the
operation and maintenance of the
Swedish road network. The harsh
winter climate in Sweden presents
the Swedish Transport Adminis-
tration with particular challenges
when it comes to operating and
maintaining the road network.
Poor visibility, caused by winter
rain, snow and fog, is a common
cause of vehicle collisions. In addi-
tion ice, which is common, causes
damage to road surfaces, making
driving difficult and leading to
higher than expected numbers of
slow or stopped vehicles, or even
pedestrians. This is true in heavy
traffic, where incidents need to be
addressed quickly to avoid more
general road network disruption.
Light traffic also gives rise to
problems, as vehicles tend to move
at greater speeds and the poten-
tial for major accidents, as the
result of collisions with stranded
vehicles, is increased. Timely
detection of incidents and posting
of warnings to upstream drivers
via motorway message signs is
imperative, therefore.
In recent times, traffic opera-
tors in the control centre in the
Swedish capital have used CCTV
to watch for incidents. Alter-
natively, reports have come via
phone, either from those directly
involved in an incident or from
passing motorists. Clearly, this
is not a reliable way to detect all
incidents quickly, to maintain lane
throughput, or to look to reduce
The Swedish Transport Administration, Trafikverket,
has installed the Clearway incident detection system
on a 16 km section of the highway e4. This covers all
lanes on both carriageways and automatically sends
alarms to the control centre when incidents occur.
Navtech Radar monitors
traffic on Swedish highway
For the surface installation, Navtech
installed two TS350X model radar
systems. The TS350X can detect a
man-sized object out to a radius of 350
metres. Since it can provide 360 degree
coverage, each sensor can therefore
provide a total of 700 metres coverage
where conditions allow.
technology in application