Traffic Data: Is FM RDS-TMC data as accurate as TrafficMaster Monitor Data from those blue posts?

As per my other post I've been looking into Sat Nav with integrated
traffic functionality. Most devices seem to use the RDS-TMC system to
provide traffic information to the devices. I understand that RDS-TMC
is a system where Traffic Message Channel (TMC) services - receive
Traffic Message Channel (TMC) data via FM radio broadcasts. There
seems to be different providers of the actual data, and Garmin (only I
think) use RDS-TMC data supplied by TrafficMaster which is claimed is
better quality data [1]

My question on the devices that use this is does it provide information
in mapping format similar to that available from TrafficMaster's
Monitor Product [2] in TrafficMaster.net style [3]

The reason I ask is because I understand that with products like
TrafficMaster Monitor [2] and TrafficMaster Freeway (an audio device
which talks to warn you of delays on the road ahead) get their data
from the roadside units on the road you are on (in fact my unit bleeps
every time it is updated) and I'm guessing that this data is very
focused on where you are. Surely FM transmissions used by RDS-TMC
cover a massive area (e.g. the area covered by BBC Radio Cambridgeshire
for example) so do such broadcasts cover all traffic information for
the entire region? Does RDS-TMC provide a level of accuracy of data
equivalent to TrafficMaster monitor? Is it provided in a similar
format to TrafficMaster Monitor.

Perhaps if anyone is familiar with both systems they could advise?

Cheers,

David

[1] http://www.trafficmaster.co.uk/shownews.cfm?num=369
"Garmin chose Trafficmaster above other UK based RDS TMC providers
because it believes that Trafficmaster offers the most accurate and
robust traffic service."

[2] Traffic Master Monitor
http://www.trafficmaster.co.uk/page.cfm?key=trafficmonitor2

[3] TrafficMaster.net
http://www.trafficmaster.co.uk/page.cfm?key=trafficmasterdotnet

[4] NavMan n60i
http://www.navman.com/Navman/Templates/productinformation____47199.aspx

[5] Garmin nuvi 660
http://www.garmin.com/uk/automotive/nuvi660.htm

I think cross posting to this group is appropriate as people in here
may have a Garmin nuvi 660 or a NavMan n60i and be able to answer the
question ;-)

davidcookoz@yahoo.com.au wrote:

Have had 1 weeks experience of my Nuvi 660 using this system. Returning from
York down the M1 to Kent between 4 @ 7pm on a Tuesday. Not surprisingly
there were multiple jams on many motorways. The device slightly
overestimated the delays on the M1 as I was travelling south. Arrival time
at home jumped from 7.40 to 10.50 at one point, ended up arriving back at
8.15!. Offered alternate routes a few times, the traffic was building quite
badly at one point so took up the suggestion, re-routed us from M1 to A1(M)
which probably saved us 15 - 20 minutes of very slow traffic.

The unit displays traffic problems as a coloured bar along the road, you get
an audible warning of traffic ahead (can be hard to tell which side of the
motorway is effected), as well as a traffic icon which you can click to get
details of alternative routes.

All in all a good system, though can be irritating at times when there are
traffic queues 'everywhere', like at rush hour, 'there is a better
alternative route available' coming out every 5 minutes can get a little
much. Also it can give you some alarming data! - namely the 10.50 arrival
time!

It should also be noted that the FM signal is variable, sometimes there is
no traffic news, when you know there has to be, other times it's fine. As
for range, it frequently gives traffic reports of 60 - 70 miles away. Not
bad if you are planning a long route.

All in all I have been very happy with the Nuvi, neat device that makes it
easy to pocket, reducing the chance of leaving it in the car and having it
stolen. Other features that are useful are JPG viewer, and MP3 player
(though the good FM transmit feature has been disabled in UK units).

Hope this helps

Many thanks for this mini-review Jon. It does help a lot! Having seen
a demonstration in Halfords of the sat nav aspects of the nuvi 660 unit
only I think I am tending towards getting a Garmin nuvi 660 rather than
a NavMan n60i. Although I have not seen the NavMan n60i a number of
people have independently commented that NavMan software is not very
reliable and more prone to failure.

Please could I ask another question? Did you get your 660 fitted to
your vehicle and is this a requirement for the traffic functionality?
I have read on a US site that the power lead acts as the FM aerial and
as such has to be fitted (i.e. the power lead fitted to get power from
the car fuse system). Perhaps this is a way of improving the variable
FM signal you mention? I was thinking of not getting the nuvi 660
fitted but just using it on battery power, but if this is a requirement
I will go for fitting.

Many thanks again,

David

One more question Jon.

On your unit, is it possible to enable the "FM transmitter" that
allows the handfree/Bluetooth integration to work through the car
speakers. An in-depth review (from the US) of the nuvi 600 [1] is very
positive, but states of this feature that "The integrated FM
transmitter is one of the best things about the nuvi 660. I was really
surprised at how much it added to the user experience."

I understand that currently FM transmission devices such as this (and
iTrip) are illegal in the UK, but it is my understanding that things
are changing and these devices will be legalized soon [2]

Thanks again,

David

[1]
http://www.gpsmagazine.com/2006/10/garmin_nuvi_660_indepth_review.html

[2] http://news.bbc.co.uk/1/hi/uk_politics/4993528.stm