Is Your GPS Naive?

mi writes "Many GPS devices today will try to scan the FM bands for traffic advisories in the area to display on their screens. The signals, however, are neither authenticated nor encrypted, and one can — with commonly available electronics — construct a device to broadcast bogus advisories. Possible codes range from "bullfight ahead" to "terrorist attack"..."

Re:great potential

[billlion]

I think people are missing the point. It is just data sent over RDS, standard FM radio in cars have this not just Sat Nav systems. Also the original post is inaccurate. Its not Global Positioning System (GPS systems), it is car Sat Nav units, they use GPS+ mapping and routing software to give directions, GPS gives you position (lat long and altitude), and often from that speed and heading etc are calculated.

Re:encryption cant help..

[Anonymous Coward]

You don't actually understand how public key encryption works, do you?

The public key is distributed far and wide, embedded in every GPS receiver in fact. This public key can can only decrypt message encrypted with a specific private key, which is not distributed.

Re:Social hack - use "bullfight" for "speed trap".

[arivanov]

How uninspiring and unoriginal. Based on my recollections from a brief encounter with Ohio cops 16 years ago I am not surprised in the slightest.

They should come here across the pond to introduce themselves to the most recent inventions in motorist taxation like:

The "Accident Assistance Van" and "Yellow Speed Camera Partnership Van". Both are in use by Sussex police and anyone driving along the A14 and A12 can see them on regular basis.

These vans can be parked with a laser speedgun + CCTV pointed through a window (back, side and front), can be parked behind a hedge with the same laser speedgun + CCTV as the only thing visible on a tripod cabled to the hidden van and most importantly can drive at 3 mph under the speed limit and record the speeds of all who overtake them showing van speed and overtaking vehicle speed.

I have seen them used in every single one of these modes of operation. In fact, out of all my A14 journeys in the last month there has been only one where I have not seen one them. None of them has proper police markings.

Re:Social hack - use "bullfight" for "speed trap".

[5of0]

Linkage for I-285 video:
http://cut-to-cure.blogspot.com/2006/03/cant-drive -55.html [blogspot.com]
Direct to video:
http://video.google.com/videoplay?docid=-536655206 7462745475&q=%22meditation+on+the+speed+limit%22 [google.com]

Re:Social hack - use "bullfight" for "speed trap".

[fractoid]

Do you really expect someone to go out to each road, and try and determine the fastest allowable speed? It is a lot easier (cheaper) just to say, every one of these roads has X for a speed limit.

Oddly enough, they don't seem to mind putting in the effort to *police* speed limits.

If we assume that each road will have a speed trap on it at least once, then they've *already got* the data to determine an appropriate speed limit as per the 85th percentile rule [ite.org]. Interestingly, as Wikipedia [wikipedia.org] notes, "a review of available speed studies demonstrates that the posted speed limit is almost always set well below the 85th-percentile speed by as much as 8 to 12 mph (see p.88) [trb.org]." This indicates that in a vast majority of cases, speed limits are set according to political rather than safety concerns.

Re:that's not what they told me

[DarkFencer]

No - you have no obligation to go over the speed limit. You do have an obligation (in almost all states - I'm not sure if Virginia is one of them) to get the hell out of the left lane except when passing. If you're sitting in the left lane while you're not passing you are more of a problem then those who are speeding (at least those only going a reasonable amount over the limit).

That being said - I usually drive the speed limit exactly (65 usually) since its better for fuel efficiency than doing 75, 85, etc.

Re:that's not what they told me

[NMerriam]

in Virginia traffic school, which I had to attend at age 16 over half my life ago. They said you do not have any obligation to move or go faster than the speed-limit whatsoever. This was from the county-enforced state-approved course taught AT the courthouse. Honestly, I think your type are assholes. But I'm too tired for a flame war right now so I will probably ignore your response.

you should probably be a little more careful about who you're repying to when throwing around "your type are assholes" responses, since I assume you were intending that for the original poster and not me. (Especially if you're trying to avoid getting into flamewars.)

And FWIW (I did live in Virginia for much of the last decade), the state law does require you to allow overtaking vehicles the left lane if they provide an audible signal that they want to pass http://leg1.state.va.us/cgi-bin/legp504.exe?000+co d+46.2-842 [state.va.us]. Every state I've ever lived in or looked up the rules for, some similar law has been on the books.

Re:that's not what they told me

[fluffy99]

Well you're wrong. At least according to the State law you're supposed to keep right http://leg1.state.va.us/cgi-bin/legp504.exe?000+co d+46.2-804 [state.va.us] and yield to faster traffic http://leg1.state.va.us/cgi-bin/legp504.exe?000+co d+46.2-842.1 [state.va.us] . According to the State Police this includes when that traffic is exceeding the speed limit http://www.fredericksburg.com/News/FLS/2006/022006 /02092006/166829 [fredericksburg.com] . Why you might ask? Because slow drivers in the left lane increase road rage incidents and cause more accidents.

Re:Now, why would there be...

[RMH101]

BECAUSE IT'S NOT A TRAFFIC WARNING SYSTEM! IT'S *RDS*.
RDS exists to allow FM radios in cars to do fun stuff like retune to a national station as you move around and the frequencies change. It also allows radio broadcasts to be flagged as "traffic" so your radio can automatically tune in and play traffic broadcasts to you.
In other words, its function is to usefully and automatically tune your FM radio to a new frequency.
The NBC "terrorism" broadcast flag is designed so that in the godawful scenario where something Real Bad happens, everyone's RDS-equipped FM radio will tune into the announcement and you'll be aware of it. AFAIK, the NBC flag on RDS broadcasts is non-discretionary - i.e. your radio *will* tune to it regardless of user input. You *can* tune away from it when you realise that the continual 4 minute countdown of incoming nuclear attack is dragging you down and you'd rather spend the remaining 3m30s of your life listening to "Freebird" whilst doing coke off your passenger...

Re:Social hack - use "bullfight" for "speed trap".

[Paulrothrock]

Highway speed limits were originally instituted to save fuel. If you drive between 55 and 60 on the highway you'll get about 10% better gas mileage. Having had to drive 40 miles each way for work each month, I figured this out very quickly.

Re:Social hack - use "bullfight" for "speed trap".

[AndersOSU]

If you drive between 55 and 60 you'll get better fuel economy if you're driving a 70s era car with a carburetor... Since the invention of fuel injectors this is much less true.