Travelers' information station
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Travelers information stations (TIS), also called highway advisory radio stations (HAR) by the United States Department of Transportation, are licensed low-power AM radio stations operated by departments of transportation, airports, local government, colleges, parks, events and destinations. The stations provide information to motorists regarding travel, situations of imminent danger and emergencies.
TIS operation in the United States
TIS stations 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, during a critical emergency. The former American Airlines TIS stations at Dallas-Fort Worth International Airport on 1640 and 1680 kHz (before the AM band expanded above 1600 kHz) ran 60 Watts power out under special exemption. The modern iteration of this station was also granted exemption 
The station audio is required to be passed through an audio low-pass filter which rolls off frequencies above 3 kHz. There have been discussions by the FCC about whether to remove this requirement as it has been found that it is not effective in reducing interference to non-TIS stations (the original reasoning for the rule) and it degrades the intelligibility of the station audio.. However most modern AM stations in the US voluntarily restrict their audio bandwith to 5khz as low as 2.5 khz. 
TIS station content is defined by the FCC as
non–commercial 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.
FCC in 2013 clarified in its Report and Order (13-98) regarding TIS stations. The Report and Order was issued as a result of a petition for clarification of the rules by the American Association of Information Radio Operators (AAIRO). (Formed in 2008, AAIRO is a nonprofit organization of operators and licensees from public agencies who manage information radio stations across the country to inform and protect motorists.) In May 2014, a Compliance Guide (DA-14-651) was issued by the FCC to summarize the Report & Order and to make it more accessible for licensees. The Report and Order and the Guide made it clear that TIS stations can be linked in "ribbons" as long as content relates to the motorist at each point in the ribbon. They also clarified that stations' content must relate to travel, emergencies or situations of imminent danger to the public - and that it is at the discretion of the station operator, based on his knowledge of his area and its population, what situations present an imminent danger to the public locally.
In the United States, only government entities 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 channel (530 kHz) and top channel (1610 kHz) on the AM band for these stations, before the AM expanded band (1610–1700 kHz) was introduced in North America. Systems may currently be licensed on any frequency from 530–1700 kHz. (Most radios tune to 1710 kHz; however, this frequency has only been licensed by FCC in one instance, by Information Station Specialists for Hudson County, New Jersey, due to the potential for an evacuation from New York City.) To the present day, 1610 kHz is used in the United States exclusively for TIS.
Usage of low-power FM stations for TIS
Low-power FM stations (LPFM) stations may be licensed to governments as well, but these are not considered part of the TIS/HAR service.
LPFM stations are not continuously available for licensing, and only during discrete filing windows. This is different from AM band TIS/HAR stations, which are continuously open for application. It is unknown if there will be future filing windows for LPFM stations. They are limited in their value for Travelers Information (TIS) or Highway Advisory (HAR) because of requirements to produce up to 8 hours of new programming each day and in certain instances to share airtime with other licensees.
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 the United States
In Germany and former Yugoslavia highways and motorways was covered with radio informations about the traffic. The new age technology have brought that these stations are rearly in use now. Radio system was designed as RDS and its aim was to interrupt current radio frequency and give travelers emergence information about the highway, updated traffic reports and weather reports, public service announcements by various governmental and public organisations, railways information, news bulletins and music. These radio system are using most in Slovenia, Croatia and partly in Serbia. Highways that are covered with traffic radio informations are:
- European route E61: Villach–Kranj–Ljubljana
- European route E70: Ljubljana–Zagreb–Sisak–Slavonski Brod–Belgrade.
- "FCC 77-414: Report and Order" (PDF). Federal Communications Commission. 20 June 1977. Retrieved 13 July 2017.
- "FCC Travelers' Information Stations Search". FCC. Retrieved 13 July 2017.
- "47 CFR 90.242 Travelers' information stations". GPO. Retrieved 13 July 2017.
- "FCC 13-98: Report and Order and Further Notice of Proposed Rulemaking" (PDF). FCC. 18 July 2013. Retrieved 13 July 2017.