travelers information stations
Histories of radio broadcasting often make a particular focus on the most powerful stations. For historic reasons, WBCT of Grand Rapids, Michigan broadcasts FM at 320ΒΈ000 watts. Many AM stations are licensed to operate at 50,000 watts, but this modern license limit represented a downgrade for some. WLW, of Cincinnati, once made 500,000. Less is made of the fun you can have under 10 watts: what we now call the Traveler's Information Station (TIS).
The TIS was not formally established as a radio service until 1977, but has much earlier precedents. The American Association of Information Radio Operators, an advocacy group for TIS, has collected some of the history of early experimental low-power radio stations. Superintendent James R. McConaghie of Vicksburg National Military Park must have been something of a tinkerer, as he built a low-power AM transmitter for his car in the mid-1950s and used it to lead auto tours. He suggested that a tape recorder might be added to provide a pre-recorded narration, and so anticipated not only the TIS but a common system of narration for group tours to this day.
During the New York World's Fair in 1964, a "leaky cable" AM system was installed on the George Washington Bridge to provide driving directions to visitors. This is the first example I can find of a low-power AM station used for traffic guidance. I can't find much information about this system except that it was the work of William Halstead, a pioneering radio engineer. Halstead is best known for developing FM stereo, but as we will see, he was a major force in TIS as well.
The National Park Service continued to innovate in radio. Low-power stations offered a promising solution to the challenge of interpreting a park to increasing numbers of visitors, especially in the era of the automobile, when rangers no longer lead tour groups from place to place. In 1968, Yellowstone acquired six custom-built low power AM transmitters that were installed at fixed locations around the park. Connected to an 8-track player with a continuous loop cartridge, they broadcast park announcements and interpretive information to visitors approaching popular attractions.
As an experiment, Yellowstone installed a five-mile "auto nature trail," a road with regularly spaced AM transmitters built for the experiment by Montana State University. The notion of an "auto nature trail" confounds our modern sensibilities, but such were the 1960s, when experiencing the world from the interior of your car was an American pastime. In a 1972 article on the effort, park service employees once again pointed out applications beyond park interpretation:
Not only is this new aspect of radio communications opening interpretation of natural areas to motorists, but the idea of being able to communicate with hundreds of motorists without having them stop their cars is a patrolman's blessing.
Along these lines, the NPS article mentions that the California Department of Transportation had deployed a low-power radio station to advise travelers of a detour on I-5 following the San Fernando earthquake. I have, unfortunately, not been able to find much information about this station---but the NPS article does tell us it used equipment from Info Systems.
Info Systems, Inc. appears to have been the first vendor of purpose-built transmitters for low-power informational stations. I haven't been able to find much information about them, and I'm a little unclear on the nature of the company--- they were apparently reselling transmitters built by vendors including ITT. I'm not sure if they were built to Info Systems designs, or if Info Systems was merely a reseller of equipment originally intended for some other application. Of course, I'm not sure what that application would have been, because at the time no such radio service existed. These transmitters operated either at milliwatt power levels under Part 15 rules, or at 10w under experimental licenses. This perhaps explains why the National Park Service figures so prominently into the history of low-power radio: as a federal agency, they presumably obtained their authorization to use radio equipment from the NTIA, not the FCC. The NTIA was likely more willing (or at least faster) to issue these experimental licenses. Info Systems transmitters were extensively installed by NPS, likely over a dozen just at Yellowstone.
In 1970, the general manager of Los Angeles International Airport became frustrated with the traffic jams at the arrival and departure lanes. He hoped to find a way to communicate with approaching drivers to better direct them---a project for which he hired William Halstead. Halstead partnered with radio consultant Richard Burden to design and install the system, and we are fortunate that Burden wrote a history of the project.
In 1972, a leaky cable antenna was buried along the median of Century Boulevard as it approached the airport. A second antenna was buried along the main airport loop, and two different NAB cartridge message repeaters (tape loop players) drove two separate transmitters. Drivers would thus begin to hear a different message as they crossed the overpass at Sepulveda Boulevard. Here, the short range of the low-power transmitters and inefficient antennas became an advantage, enabling a fairly small transition area between the two signals that would otherwise interfere.
Each of the message repeaters had three different cartridges they rotated through: a list of airlines using each terminal, parking information, and traffic information. Some of these recordings, like the traffic information, had different prerecorded variations that could be used depending on the weather and traffic conditions.
An interesting detail of the LAX radio system is that it was coupled to a new signage strategy. During development of the recordings, Burden realized that it was very difficult to direct drivers to terminals, since the terminal numbers were indicated by high-up signs that weren't noticeable from road level. Brand new signs were installed that were color coded (to identify terminals or parking areas) and bore large terminal numbers and a list of airlines served. The signs from this project were apparently in use at LAX at least until 2012. There is, of course, a lesson here, in that any new interpretive or information system will be most effective when it's installed as part of a larger, holistic strategy.
LAX's new traffic radio station operated at 830 kHz under an experimental license. Unfortunately, early experience with the system showed that drivers had a hard time tuning to 830 kHz using the slider-type tuners of the era, creating a dangerous wave of distraction as they passed the signs advertising the new radio station. Burden wanted to move the station to an extreme end of the AM band, where drivers could just push the slider until it stopped. Unfortunately, 540 kHz, the bottom of the established AM band, was licensed to a Mexican clear-channel station and could not be allocated so near to the border. Instead, Burden convinced the FCC to allow an experimental license for 530 kHz: the vast majority of cars, they found, would receive 530 kHz just fine when tuned to the bottom of their range. The frequency was formally allocated for aviation NDBs, but not in use at LAX or almost any other airport. Thus we have the origin of 530 kHz as one of the two standard frequencies for TIS [1].
By 1973, the FCC had started the rulemaking process to create a 10w TIS radio service. The National Park Service, apparently wanting to take a conservative approach to equipment purchasing, chose to stop buying new low-power AM transmitters until transmitters certified under the new FCC rules were available. In practice, this would take four years, during which time the lost sales to NPS were so great that Info Systems went out of business.
During this period, a company called Audio-Sine continued to manufacture and promote Part 15 AM transmitters---but for a different application. The "talking billboard," they proposed, would improve outdoor advertising by allowing travelers to tune their radio for more information on a product they saw along the roadside. The talking billboard concept never really caught on---a prototype, in Minneapolis, advertised for the idea of the talking billboard itself. "Look for talking billboards throughout this area in the near future." At least one other was installed, but in Duluth, advertising for Dean Nyquist's primary race for Minnesota Attorney General. "The Audio Sign... gives a very positive pitch for the City of Duluth..." the campaign manager said. "I would advise the city or chamber of commerce to use one or more all the time." I wonder if he was invested in Audio-Sine. A newspaper article a few days later comments that the talking billboard apparently did not work, something the same campaign manager attributed to a railroad trestle blocking the signal.
This is an obvious limitation of Part 15 AM transmitters: the power limit is very low. Audio-Sine only really claimed a range of "4-8 blocks," and today I think you would struggle to meet even that. The more powerful 10W stations, operated under experimental licenses, could reach as much as eight miles in good conditions.
Despite their limitations, the Audio-Sine milliwatt transmitters did find some use as early equivalents of TIS. This overlap does make it amusing that when the California Department of Transportation introduced their first changeable message signs around the same time, they called them "talking billboards" in the press.
There exists to this day a "microbroadcasting" hobby, of individuals who operate low-power FM and AM transmitters under Part 15 rules. To these hobbyists, who are always looking to transmit the best signal they can within the rules, the specific technical details of these early transmitters are of great interest. They remain, to this day, just about the state of the art in intentional broadcast radio transmission within Part 15 rules. In fact, the availability of these commercially-manufactured low-power AM transmitters seems to have lead to a short-lived boom of "whip and mast" Part 15 AM stations that attracted the attention of the FCC---not in a good way. Various details of our contemporary Part 15, such as the 3-meter antenna, feed line, and ground lead limitation of 47 CFR 15.219, seem to have been written to limit the range of the early 1970s Info Systems and Audio-Sine transmitters, along with a few other less prominent manufacturers of the day.
There are historical questions here that are very difficult to answer, which is frustrating. The exact interpretation of the limits on Part 15 intentional radiators are of great interest to hobbyists in the pirate-radio-adjacent space of legal unlicensed broadcasting, but the rules can be surprisingly confusing. You can imagine this leads to a lot of squinting at the CFRs, the history, and what exactly the FCC intended the rules to be when they were originally written. The fact that the FCC actually enforces according to a booklet of standards that it won't release but may be based on 1970s installation practices only makes the matter more intriguing.
In 1977, the FCC promulgated Part 90 rules formally establishing the Traveler's Information Station/Highway Advisory Radio service. TIS were allocated 530 kHz and 1610kHz, the two extremes of the American AM broadcast band at the time. Incidentally, the AM broadcast band would later be extended up to 1700kHz, but TIS on 1610 has not been moved. 530 and 1610 remain de facto exclusively allocated to TIS today. TIS rules remain largely unchanged today, although there have been some revisions to clarify that the established practice of "ribbons" (sequences of TIS transmitters) was permissible and to allow 5 kHz of audio bandwidth rather than the former 3 kHz.
Part 90-certified TIS transmitters are now commercially available from several manufacturers, and widely installed. Power is limited primarily in terms of field strength, although there is an RF output power limit as well. Leaky cable systems are permitted up to 50 watts into a 3 km long antenna to produce a field of 2 mV/m at 60 m from the antenna; conventional antenna stations are limited to 10 watts power into a vertically polarized antenna up to 15 m high and a field strength of 2 mV/m at 1.5 km. Most TIS installations are "whip and mast" types similar to those at the genesis of the category, using a monopole antenna mounted at the top of a signpost-type mast with the transmitter in a weathertight enclosure mounted to the side of the mast. You learn to recognize them. Typical coverage for a TIS station is 3 km (indeed, that is the limit on the planned coverage area).
Searching for TIS licenses is a little odd because of the formalities of the licensing. All TIS licenses must be issued to "government entities or park districts," in part because TIS is technically part of the public safety pool. The AM frequencies allocated to TIS stations are sort of "transferred" to the public safety pool (on a primary basis for 530 kHz and secondary basis for 1600-1700 kHz). In other words, TIS licenses are best found in ULS by searching the PW (public safety pool, conventional) service for frequencies between 0.530-1.700 MHz. There are 1,218 such licenses active.
I'm not going to provide a breakdown on all thousand-plus licenses, but I did take a quick look for any "interesting" entries, and some boring ones as examples of a typical application.
Consider the very first result, KMH441, licensed to the State of Illinois for 1610 kHz. It appears to have a surprisingly large tophat antenna. It probably serves weather advisories for the nearby freeway. Rather dull, but most TIS are just like this, except with less impressive antennas. KNIP553 is licensed to the Foothill-De Anza Community College District Police in Los Altos Hills, CA, at 1610 kHz as well. It's probably on the roof of one of the campus buildings. Like most TIS, there are essentially no mentions of this station on the internet, except in listings of TIS based on licenses.
KNNN871 1610 kHz is licensed to the city of Vail, Colorado, and this one got a local news article when it was installed. There are two transmitters. WNKG901, Greater New Orleans Expressway Commission, is on 1700 kHz and has four licensed transmitters at various toll plazas. The transmitters are standard whips on masts, but this one is in an unusual place.
WNRO290, State of New Mexico, operates at 530 kHz at the St. Francis/I-25 interchange in Santa Fe. The transmitter is totally typical and shoved into a median space.
WPEZ840 is assigned to the Lower Colorado River Authority and covers 1610 or 1670 kHz at six locations, each a power plant (some of them hydroelectric, but the Lower Colorado River Authority apparently operates some coal plants). Like many emergency-oriented TIS, these stations normally rebroadcast NOAA All-Hazards Weather Radio.
While TIS are limited to government agencies, there are definitely some cases of private organizations finding a government sponsor to obtain a TIS license. For example, Meteor Crater in Arizona has signs at the freeway advising that there is attraction information on 1610 kHz. This is WQDF361, which is actually licensed to the nearby City of Winslow. Like many TIS stations, the license contact is Information Station Specialists, a company that specializes in TIS including both equipment and licensing.
Because TIS are ubiquitous low-power AM stations, some DX (long-distance receiving) enthusiasts will try to pick up very distant TIS. Historically, some TIS operators would issue QSL cards. Considering that there are quite a few TIS in service that are government-registered but seem to be physically maintained by radio clubs or amateur radio operators, there are probably still a fair number out there that will return a QSL card if you try.
Having discussed TIS, we finally need to consider the fact that there are a lot of things that look and feel like TIS but are not. Most notably, when the Low Power FM (LPFM) class was established in 2000, one of the authorized functions of LPFM stations is something that is very much like, but not quite, TIS. A notable advantage of LPFM stations for this purpose (besides the higher popularity of FM radio despite its poorer range) is that the license class explicitly allows large-area networks composed of many low-power transmitters---something that is kind-of-sort-of possible with TIS using very long "ribbon" sequences, but not encouraged. These rules mean that TIS-type LPFM networks can feasibly cover multiple towns.
A major example is in Colorado, where the state operates eleven LPFM stations such as KASP-LP, 107.9 FM Aspen. Anyone familiar with the extreme difficulty of actually getting LPFM licenses will be rather jealous of the State of Colorado for bagging eleven, but then government agencies do get preference. The Colorado stations rebroadcast NOAA All-Hazards Weather Radio with 100 W of power, mostly just allowing people to listen to them without having a tuner capable of covering the 160MHz weather band (an unfortunately common problem).
It's hard to know what the future holds for TIS. The broad decline in AM radio suggests that TIS may fade away as well, although it appears that AM receivers will be mandated in vehicles sold in the US. Some states, such as Virginia, have significantly reduced the number of TIS in operation. Still, some TIS systems are popular enough with drivers that plans to eliminate them lead to public objections. Most TIS operators are increasingly focusing on emergency communications rather than traffic advisories, since TIS offers a very reliable option for communications that is completely under local control---very local control, considering the short range.
[1] Wikipedia suggests that an NDB on 529 kHz at Manchester, TN can be heard in many parts of the US. There's a weird lack of basic information on this NDB, such as its location or the name of the airport it is located at. It seems to have been installed at a private airport by an amateur radio operator, probably as more of a hobby project than anything. I cannot find it on contemporary charts or even find an airport that fits the description, and I don't see references to it newer than 2009, so I think at least the NDB and possibly the entire airport are gone to history.