Welcome to the Garmin GTM 25 Traffic Receiver (SUNA compatible Traffic Receiver) review.  This is a series of Garmin accessories designed for their Nuvi portable GPS systems.  The GTM 25 is mainly designed for the Nuvi 265W, 255W, 205W, 265, 255 and 500 series and all new Nuvi 1000 series. 

This accessory when connected to a compatiable Garmin GPS will upgrade it to the 'T' series.  Eg. 265W will now have 265Wt functionality!

It basically a FM receiver built into the power cord of the Garmin GPS. If you want it built in you'll need a model with a T at the end. But make sure you check the specs anyway to make sure it's built in or otherwise.  The built in models are about $100 more than those without. The TMC traffic signals are not everywhere and often limited to the city areas. 

The Garmin GTM 25 is a FM-RDS TMC receiver that allows the GPS unit to receive live traffic information broadcast over radio waves.  The traffic information is provided by various organisations around the world.  In Australia it is an organisation called Intelematics and the brand the system is marketed under is SUNA name.  You can get other SUNA compatible systems in Australia but if your GPS unit doesn't have the internal software to use the traffic information it won't be of any use.  The traffic information is provided free (In Australia).  Only the  latest GPS systems have this capability.

I guess this writeup is more a SUNA review rather than the GTM 25 one because it is really the traffic data and related software rather than the receiver its self... 

As you can see from the picture the GTM 25 basically replaces the Garmin's original car based power cable.  The cable has a slight bulge that it the receiver unit.  It's antenna is built into the power cable but an additional antenna is also provided in the box but you don't need to use it if the signal is strong in your area.  I didn't need to use the external antenna.

Just plug the new cable into a compatible Garmin and power it up.  Because the GTM it's not built in you need to turn the car on before it will start to get the traffic information. This is the only issue I have with an external traffic receiver. You'll know its working once a green car symbol on the left appears on the main map screen.

If you have a Garmin with the built in TMC traffic receiver you'll have the same options experience as I'm describing.

Where available the road's speed limit is displayed. (even without the GTM attached)
The speed limit details are NOT accurate because they don't update automatically.
Another airport and anther city - what's the traffic like? Press the green button!

Pressing the green button will activate the traffic menu which has a few more options to show the traffic version of the map, search for traffic and . It's all logical and easy to use.

The search function shows all the traffic in the database.
Since I tested this at night there's not much to see.

I was surprised at how much information the SUNA system or any other brand distributes and that it works regardless of whether you've programmed a destination in or just simply viewing the screen.

This is the wider view with a few more details.
When you get off a plane and wonder how the traffic is like in the city.

As for avoiding the traffic problems - yes, it does seem to work but the directions can appear odd if traffic is moving albeit very slowly so there does not appear to be a reason to change route...if the traffic situation changes.  Furthermore there are very few opportunities to exit a blocked free way unless you plan ahead.  Remember the information is supposed to be live!  More updates as I test it in proper high traffic and pressure situations...

The traffic data that is shown include: Road works, Traffic accidents, heavy traffic, moderate traffic, Hazards...

Conclusion so far: Is TMC useful? Does the SUNA network work?  Is simply listening to the radio just as good?  Each to their own really but if you are travelling to a destination in a big city that does have traffic problems and that you really aren't familiar with then yes! Besides regular radio station updates aren't frequent enough for my liking and why wait when the GPS will tell you in advance of problems.  Beats listening to some often pointless person on the radio and some very poor choice of music.

Since I just got the GTM 25 (ie. 4 days ago) I haven't had the full experience with it just yet so I'll give update the page in a week or so with a proper conclusion.  You cannot do the system justice by simply reviewing one uneventful and less traffic ridden trip.  It will be more interesting since I'll be away from home once again.

For the time being the system has great potential and I would like it as a standard or built in receiver BUT its usefulness is limited to high traffic city areas AND I wouldn't pay for subscription data if it became chargeable because of this.  Maybe if it detailed ALL road works not just the major ones or even festivals that could be avoided.  Nonetheless having a SUNA compatible GPS is a great idea...