Highway advisory radio

Highway advisory radio (HAR) transmits audio traveler information messages via radio to travelers within range of the signal. Roadside signs inform travelers of the radio frequency and often use flashing lights to alert travelers of advisory messages.

Key characteristics





WSDOT regions

Other names

  • Traveler's information station

Strategy description

Highway advisory radio (HAR) provides timely traffic and travel condition information en route to motorists. HAR systems broadcast an AM radio signal over specially reserved, low power radio frequencies to provide audio messages to vehicles.

HAR operations

Operating a HAR system requires a Federal Communication Commission's (FCC) permit in order to broadcast on the reserved frequencies. However, FCC regulations limit the broadcast power of HAR systems in order to minimize interference with commercial radio broadcasts. This limits the effective broadcast range to one to two miles and makes the transmissions highly sensitive to interference from buildings, electric lines, and weather. 

Typically, a central message distribution system operated at a traffic management center (TMC) is used to record new messages, store pre-recorded messages, and distribute messages to transmitters in the field.

HAR signage

Roadside signs are typically placed in advance of the HAR transmitter to inform travelers of the radio frequency and often use flashing lights to alert travelers that an advisory message is being broadcast.

Positives and negatives of HAR

One of the primary advantages of HAR as compared to other traveler information strategies, such as roadside variable message signs (VMS) or mobile apps, is that it can provide a larger amount of information due to its audio format, and do so without imposing a visual distraction. Additionally, it can reach more travelers than a VMS and only requires an AM radio to receive the broadcast.

A significant disadvantage of HAR is that it often suffers from poor signal quality, which limits the reliability of the system to convey important information to the traveling public. It also requires the driver to take an action to turn on the radio or change the station or both. This can lead to low levels of access to the information.

When to use this strategy

HAR makes sense for locations where travelers routinely need information (e.g., the entrance to mountain passes) or before locations where travelers must make a routing decision. It can also support active traffic management strategies where having a means to provide en-route traveler information is a core element of the strategy.

HAR is especially valuable in rural settings where cellular connectivity may be weak and AM radio broadcast may be the most effective way to provide traveler information to the largest audience possible

Strategy benefits:

  • Improves traveler decision making, which can improve safety, reduce congestion and travel delay, as well as decrease traveler frustration
  • Reduces collisions by alerting drivers to slowed or stopped traffic ahead
  • Can provide more information than other traveler information approaches, without imposing a visual distraction
  • Allows all travelers with AM radio—a technology that nearly all vehicles have—to receive messages when they are within range of transmitters. Radio has minimal data transmission cost and does not require any technology know-how

What you need in order to implement

Policy needs:

  • Development of message prioritization rules to ensure that critical messages are broadcast when needed
  • Clear and direct language in messages that allows for quick and easy comprehension

Planning needs:

  • Federal Communications Commission (FCC) approval to operate a HAR system
  • Analysis to determine the number, placement, and type of HAR transmitters necessary to provide traveler information effectively (e.g., a HAR placed well upstream of a major interchange allows travelers time to tune to the station, listen to the message, and reroute safely)

Equipment needs:

  • Radio transmission equipment along the roadway to broadcast AM signals to motorists
  • Central message distribution system to record and/or automatically generate message content and distribute to multiple HAR transmitters in the field
  • Signage upstream of HAR transmitters to alert travelers of current announcements

Maintenance needs:

  • Regular maintenance of the HAR system to ensure the transmitters are broadcasting clearly and reliably

Agency resources needs:

  • Traffic engineers to place transmitters and establish proper messaging
  • TMC operators to operate and monitor the HAR

Learn more about this strategy

Federal Highway Administration (FHWA), Freeway Management and Operations Handbook, Chapter 13.2.7. https://ops.fhwa.dot.gov/freewaymgmt/publications/frwy_mgmt_handbook/chapter13_02.htm

Federal Communications Commission, Travelers’ Information Stations Search (describes HAR guidelines and lists currently existing HAR stations by state).

About key characteristics

Location notes:

HAR works best for high volume corridors and primary routes where travelers would benefit from getting information about incidents, travel times, detours, or special events. It is also suitable for rural settings where cellular connectivity may be weak. Urban areas present challenges due to the interference impacts of tall buildings and electric lines.

Cost notes:

HAR costs vary depending on the number of transmitters installed along the corridor and the extent to which existing power and communications is available at potential transmitter sites.

Technology notes:

HAR message transmission uses standard, well-established AM broadcast technology. Sophisticated central software may be required to generate automated messages.

Collaboration notes:

Collaboration needs are relatively low as the HAR system is typically operated by a single agency (usually a state DOT) on that agency’s roads. However, some collaboration with external agencies may be necessary in order to broadcast a broader range of traveler information from various sources.