October 2, 2006

What is TMC Traffic?

The TMC stands for Traffic Message Channel, and is a great way to get Traffic issues sent to your GPS via FM signals that can’t be picked up by a normal FM car stereo. TMC is a specific application of the RDS or Radio Data System for silently transmitting information like traffic and weather over FM signals. This data-only traffic signal is sent out via ClearChannel communications (in the US), with data provided by Inrix, a large aggregator of traffic information. This TMC signal gives you easy real-time warnings of tie-ups, accidents, slow traffic, and allows you and your GPS to avoid these messes, and is always on. The service is available in about 50 cities across the US. The ClearChannel System has an advantage over traffic.com based systems because it has a broader reach and can get you traffic information on more roads that the competition. Here’s why:

XM – Relies on road sensors that monitor vehicle speeds with an installed network of radar towers along the sides of the road. You’ve probably seen these skinny little towers about 60 feet high about every mile going down the highway near cities. Those towers monitor the flow of traffic and send it ultimately to your GPS.

ClearChannel and TMC – this data collection system is run by Inrix, and they too use installed road sensors. They also use a large network of fleet vehicles with on-board GPS units that transmit back their speed and route information. These fleet vehicles are delivery trucks, taxis and freight vehicles that already have the GPS on board and are now little traffic reporters wherever they go. This network of over 600,000 vehicles nationwide is called the “Dust Network”, and this network allows Inrix, and ClearChannel to get traffic flow data on roads that don’t have hard-wired sensors on them. A recent study showed that the Dust Network worked as well as a hard wired network for predicting travel time and telling traffic flow conditions. The study also confirmed that Inrix has much broader coverage. In some cities this meant twice as much coverage, in some cities this meant up to eight times as much coverage in terms of miles of road covered. Aside: TomTom uses a Bluetooth connection to your mobile phone to download traffic data from the Inrix database, so the data feed quality should be the same as TMC.

Why should you want TMC Traffic?
Garmin’s use of it is a great way to illustrate how this works. If your unit is equipped with TMC traffic, a little icon will pop up in the corner of the screen if there is a traffic incident on your route that you are navigating. Tap on the icon and it brings you to an alert page where you can see how severe the incident is. The warning is color coded Yellow or Red to indicate the severity. Tap another button and the GPS can find a way around the traffic issue.

Cost of TMC
Most companies in the US give a 3-month free trial of the TMC traffic service. After that, the fee is around $60 per year. If you live in a congested city, and commute through heavily traveled roads, the $60 fee will probably save you a few hours of time per year, easily, and is well worth it. The system is over a year old in most cities and is getting better all the time.

Garmin C550 and TMC Traffic
I reviewed the Garmin StreetPilot C550 and thought that it was a great little GPS. What stood out was the TMC traffic receiver that was built right into the 12-volt power adapter, and was so seamlessly integrated into the software, it was easy and intuitive to use right away. I said that it was “Worth its weight in gold.” Read more at GPS Review: Garmin StreetPilot C550 Review by GPS Lodge

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Posted by Scott Martin at October 2, 2006 8:52 AM

Recent Comments

I just got this TMC adapter for my Nuvi 350. I have been monitoring it all day since I activated it. I have noticed it might miss a few incidents, some that aren't really on major freeways, and those that aren't congesting the area. It is keeping up with the website feed from the local news station here in KC, so I think it is worth it if you rely on checking the internet for your traffic information, this may become of use to help reduce the consistent need. I've mainly driven I-35, I-435 on the south and east loop, I-470, and I-70. I know all of these get real bad bottlenecks when something even minor occurs. I wished I had this while I was still in school, might have helped keep the gray hairs away from worrying so much about what was ahead to get to school on time. Go here to this link to get more information on coverage. It also tells you which station is hosting the service.


Posted by: Matthew at January 2, 2009 7:24 PM

Sounds great, in theory. Unfortunately, the reality, at least here in metro Boston, and most of New England, doesn't live up to the promise. I have found that after a year of extensive real life use, TMC traffic info is no better than the traffic info you get from your am radio. All to often was I alerted to traffic that didn't exist, or not alerted to traffic I found myself sitting in. The former has the potential of really adding to your drivetime if it makes you take secondary roads, as mine has, in place of highways due to a fictitious report. Definitely not worth 60 bucks a year. If you can get it for free, and deal with potential false info, it's better than nothing, otherwise, at least until the info and data is improved, save your money

Posted by: David at November 17, 2008 6:59 AM

where can I get TMC subscribe in Toronto area?

Posted by: qianwanli at September 9, 2008 2:12 PM
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