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Low
Power FM radio stations are usually owned by local businesses or community
groups. Broadcasting over a small, local area, these stations are typically
used to disseminate local information over a 15 mile range. Realizing
the potential of this dissemination medium, Departments of Transportation
began to use LPFM to disseminate traffic and travel information over
a small area.
Low
Power FM stations use much less powerful equipment than regular FM stations.
LPFM uses the same broadcast frequencies as regular FM, and can be received
on standard car radios. Low Power FM (LPFM) broadcast stations can now
be licensed on frequencies throughout the FM band at powers of up to
100 watts. Using a 100 foot tower or a natural hill, high quality coverage
is possible over a 12 to 20 mile diameter. Several states (including
Colorado, Iowa, New Mexico and Vermont) and some turnpike operators
have applied for networks of LPFM licenses. Castle Rock has implemented
four LPFM stations to date: three in Iowa and one in Vermont.
LPFM
for DOTs is intended to augment traditional traffic information updates
that can be heard on nearly every full power FM station. Licenses
for specific locations were obtained during FCC licensing windows
based on specific corridor needs. DOTs also deploy roadway signs before
and after the station on nearby interstates or state highways to alert
drivers to the service. The roadway signs typically state a simple
“tune-to” message and display the station’s FM frequency.
Castle
Rock has taken LPFM one step further than static messages and implemented
an automated process that updates individual LPFM stations as events
are entered into a states CARS system. Messages are passed to a central
hub that distributes messages to a specific station in a form that complies
with national transportation messaging standards. The individual station
software parses the messages based on pre-defined rules, and then queues
them for transmission. The software also accommodates the ability for
states to record, update and queue their own messages in addition to
the standard message sets.
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