Highway advisory radio
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Travelers Information Radio Stations (TIS), are sometimes also called Highway Advisory Radio Stations (HAR) by Departments of Transportation in the United States. These radio stations are licensed low-power AM radio stations set up by local transport departments to provide bulletins to motorists and other travelers regarding traffic and other delays. They are often near highways and airports, and occasionally other tourism attractions such as national parks. In the latter case, they often provide a loop of prerecorded information about the park's historic and other background information.
These systems are licensed by the FCC in the United States under 47 CFR Sec. 90.242 and are limited to a maximum signal of 2 mV/m at 1.5 km (0.93 mi) using a power of up to 10 watts to achieve this limit in the case of vertical antenna systems (the most common type). Up to 50 watts in the case of the radiating cable antenna systems may be used to achieve a maximum of 2 mV/m at 60 m (200 ft) from the radiating cable. Radiating cable systems are limited to a continuous antenna length of 1.9 km (1.2 mi). Cable systems are used for situations such as Dulles International Airport with very long limited-access approach roads where multiple systems can be placed in 1.9 km segments.
Critical evacuation systems, such as those in the Florida Keys and near chemical and nuclear facilities, have been granted exceptional power waivers for emergency operations. These systems will typically operate under the normal power level, but have permission to exceed that limit, typically to 100 W, in the face of a critical emergency evacuation situation.
The audible signal is required to include an audio low-pass filter which rolls off frequencies above 3 kHz. Content is defined by the FCC as "noncommercial voice information pertaining to traffic and road conditions, traffic hazard and travel advisories, directions, availability of lodging, rest stops and service stations, and descriptions of local points of interest. It is not permissible to identify the commercial name of any business whose service may be available within or outside the coverage area of a Travelers' Information Station. However, to facilitate announcements concerning departures/arrivals and parking areas at air, train, and bus terminals, the trade name identification of carriers is permitted."
In the United States, only governments may have licenses for TIS/HAR stations, with some exceptions granted for quasi-governmental agencies and authorities as well as health and emergency service providers working in conjunction with governmental entities. The FCC formerly reserved the bottom and top channels (530 and 1610) on the AM band for these stations, before the Extended AM broadcast band (1610 to 1700) was introduced in North America. Systems may currently be licensed on any frequency from 530–1700 kHz. (Most radios tune to 1710; however, this frequency has only been licensed in one instance, by Information Station Specialists for Hudson County, New Jersey, due to the potential for an evacuation from New York City.)
A national group of station TIS/HAR station operators called the American Association of Information Radio Operators (AAIRO) is a no-charge national forum for station operations and offers services for station licensees. AAIRO is accessed at www.AAIRO.org. AAIRO members include cities, counties and federal entities which operate the stations, as well as interested parties and founders of the service. AAIRO members free services such a message recording and also receive a newsletter exclusively about topics related to Information Radio at www.theRADIOsource.com.
LPFM stations may be licensed to governments as well, but these are not considered part of the TIS/HAR service. Stations for U.S. national parks and other units under the U.S. federal government are licensed by the NTIA rather than the FCC.
In some states, LPFM stations are used to broadcast travelers information. Colorado has a statewide network of LPFMs used in this manner, while many other state, county, or local governments use one or more stations. Examples include WTUS-LP in Tuscaloosa, Alabama, operated by the Tuscaloosa Convention and Visitors Bureau; and WGEO-LP in Georgetown, South Carolina, which is operated by the Georgetown City Fire Department.
Outside of the United States 
The concept is not limited to the US: TIS stations operate in Canada (on both AM and FM bands), in France (at 107.7 MHz FM along selected autoroutes), in Australia in some areas on 87.6–88 MHz FM, and other countries as well.
See also 
- FCC's directory of TIS stations
- (French) Information on French Autoroutes-Info stations You can listen to streaming audio from these stations as well.