How does the Traffic Alert function on a car radio work?

I was asked this question the other day in The Pirates and the Economy and the answer should really be in the form of a question. How does your radio know what the name of the radio station is?

Basically the answer is that the radio signal has a data signal that is sent along with it. This is very similar to the way that teletext works on television but with much less data.

For each radio station there is a set of different data that gets sent with certain identifiers. These data change for each radio programme and so it is possible for the radio to tell you which station you are listening to and even which program. The system for this is called RDS (Radio Data System [RBDS in America] – easy to confuse with the other acronym floating about for radio in Europe which is DAB even though it contains none of the same letters – DAB is digital radio RDS is data being sent via FM).

One of the identifiers is TA which means traffic announcement. This means that the station is playing a traffic announcement right now and so you should probably stop what you’re doing and listen to the radio. This basically only works if are tuned in at the moment that the station starts broadcasting the TA signal. But what if you want to listen to any traffic announcement not just one from the station that you were listening to before you put the CD player on?

Well in that case you need a different signal TP (Traffic Program – versus Traffic Announcement) this means that the station regularly has Traffic Announcements and so it’s worth paying attention to. Generally the way that most modern radios work is that they scan all of the radio stations once, and pay attention to any which have the TP signal. Then they scan just the ones which have TP, and watch for a TA appearing on any of them. And if one appears then they stop the CD or tape and play the appropriate radio station.

EON (Enhanced Other Network) is the original way that this was supposed to work which suggests to you other stations which broadcast traffic info. So BBC Radio 1 would suggest the local BBC station or Radio 2, 3, 4 or 5 to you. But the new method of monitoring all of the stations is a good way of dealing with the situation – this only really works if you aren’t actively listening to the radio though. Most car radios only have one tuner which means that they rely on using EON to tell which other radio stations are playing traffic news if you’re listening to the radio. But once the radio is off (or you’re listening to a CD) it can be from any station that you would get your travel news.

Although most stations don’t do it (or certainly most radios don’t receive it) the station could in fact display track info or information about the show on RDS. The BBC is one of the few broadcasters to bother doing this in the UK but you may find that your radio does not display it.

At one point the fact that the system automatically played track information played merry havoc as Simon Mayo’s quiz where people had to guess the name of the obscure tracks he was playing was ruined somewhat by the fact that a select band were being provided the answers by the radio itself!

8 thoughts on “How does the Traffic Alert function on a car radio work?

  1. Nick Ollivère says:

    For some reason the Traffic Alert function is something I’ve always found quite magical. When was it first introduced? It seems as though it was a piece of technology ahead of its time. The great thing about it is when you’re driving across England it will pick up local radio stations in each area you arrive at, giving you up to date and specific information about upcoming roads. Outstanding. It’s the simple things in life that matter.

  2. Nick Ollivère says:

    And who invented it?I also have another question regarding the Black Museum, but should perhaps save it for later…

  3. rkelly9 says:

    would it be possible to pick up the data from a specific song? say all the songs had data attached and you could list your favourite songs of the week then like the TA the radio would pick ur favourite songs up using the data attached or would this be too complex/not possible

  4. Alex Andronov says:

    That’s quite a good idea rkelly9. Not sure exactly how it would work but it could be the answer!

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  8. Clare Reeves says:

    Is it possible to ‘select’ the local radio stations for traffic announcements? I live in Bristol and I not interested in road problems in North Wales or Hereford and Worcestershire but they come along with Bristol, Somerset, Gloucestershire and Wiltshire – sometimes more traffic announcements that programmes.

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