RDS and TMC
You know that you can receive information on traffic updates to your GPS, but did you know that this information comes from the RDS-TMC traffic receiver in your GPS? Most likely, you had no idea. But, what exactly is RDS-TMC?
Well, RDS stands for Radio Data System while TMC stands for Traffic Message Channel. Basically, TMC is hosted by Clear Channel Communications, and these messages are sent to the RDS. The RDS will then broadcast the message and provide drivers with information about traffic problems via the FM channel airwaves.
Every traffic event that occurs is sent as a TMC message. This message will contain information such as what type of event it is and the coordinates of the event. These messages can usually be sourced back to police data or traffic cameras, but it may also come from other sources as well.
Traffic incidents can be nearly anything having to do with the traffic. This includes accidents, construction, non-working traffic lights, bad weather or even a busted water main. Regardless of the type, they all fall under the traffic incident category and are reported as a TMC message.
The location code of each event comes from location code tables, which are based on location table points throughout the country. Points are spread out in irregular patterns, and one point may encompass more than one area. These codes are given a number based on the road where the event is located, and these codes are kept up on a national level.
How It Works
But, how does this relate to GPS units? Well, RDS-TMC antennas can also be added to cars, and many of these come with their own car GPS unit. Or, the antennas can be added to the vehicle’s GPS system. These antennas are meant to be added to the car via a suction cup that can be affixed to the windshield.
These systems will then provide information on traffic flow, accidents, weather and other data related to traffic conditions. This allows the user to locate where problems are and avoid them if they can.
The RDS-TMC systems are great for long road trips, where drivers are not familiar with traffic conditions. Or, commuters can use them to figure out which areas are the least congested during high driving times.
While the RDS-TMC information can be very useful to drivers, there have been some complaints with the systems. It’s hard to tell the exact locations of many traffic incidents. What happens is that the location tables cause information to be slightly unreliable when it is downloaded to the traffic receiver for the GPS units.
This problem lies in the fact the location codes have to be placed over the map that the GPS is using. But, location codes are not precise. The location table point for the code may actually be several miles away from the actual traffic incident.
This could cause the driver to believe that they are avoiding the problem when they are actually driving right into it. And, the GPS won’t know to reroute the driver since the location code has the traffic problem located in a different area.