If your car is installed with a GPS system then speed limit information for each street, intersection of every county, city and state should be available too. I see no reason for people driving having to look out the window constantly in search of speed limit signs. Ideally what should happen is that the GPS System feeds the information to the Speedometer which changes the dial color from green to red (or any other format) so that the driver knows that he is crossing the speed limit. Once can then adjust speed and save paper and money.
-- nomadic_wonderer, Mar 31 2004

INFATI... http://www.infati.dk/uk/isadiv.htm
"...a Danish acronym for "INtelligent FArtTIlpasning" - which is Danish for Intelligent Speed Adaptation (ISA), which is the generic term for a variety of techniques for speed support with traffic information, which primary purpose is to improve road safety. The systems help the driver to observe the speed limits." [phoenix, Oct 04 2004]

I like this idea, but would be happy with a sliding post on the face of my speedometer which kept track of the localized speed limit. This would get rid of the problem of posted limits being obscured by foliage, passing vehicles, poor placement, or other obstructions. And it would be readily verifiable by both the driver and highway patrol officers at the time a ticket was being issued.
-- jurist, Mar 31 2004


If you are on cruise control it should take down the speed automatically.
-- kbecker, Mar 31 2004


Why not install transmitters on each speed limit sign that broadcast the speed limit posted at that point?

Using GPS, you'd have to have a speed data file that maps your current location to a speed limit. And a new file would have to be transmitted everytime a speed limit was changed somewhere.

With individual transmitters, the road maintainance crews could adjust the setting any time they replace the signs (they gotta go out there anyway).
-- b00ber, Mar 31 2004


[b00ber] I think the cost of installing a transmitter on every speed limit sign will outstrip the cost of having a central updatable database by a huge magnitude.
-- nomadic_wonderer, Mar 31 2004


Here in Australia they're trialing a new speed detection system for freeways, where your numberplate is recorded at one point, and 20km down the road it's recorded again. If you got there too quickly, you're nicked.
-- simonj, Mar 31 2004


Thats been done already [www.blackspot.com.au] only has Australia and New Zealand on that particular site, but i know england has them and I'd bet my life that the U.S does too. Doesn't just show speed limits, but as the URL suggests it alerts you to black spots, also school zones, rail crossings, and where red light and fixed speed cameras are. You can also add your own points for those spots you have seen police before. For long distance drives in areas you don't know its worth every cent
-- hatch, Apr 01 2004


I have used my Benefon Esc GPS phone to tell me my true speed limit when I am in doubt. My speedometers on both cars are quite off.
-- Frostybeard, Apr 01 2004


Frosty GPS can be off to have seen some very silly speeds measured using gps that could not have been achived
-- engineer1, Apr 01 2004


The map databases in Europe now start contain this kind of data. So speed limit info will be on European navigation systems soon. US may follow later?
-- Frederik De Vusser, Apr 29 2004


Hey bakeyees. Inspired, a couple of us built this thing using a PIC. [gpscruise.com] So far it beeps if you speed and hooks to normal cruise control. We need your help in building a list of all speed limit signs. Be immortalized by owning/adding your own speed limit sign!
-- carterson2, Aug 09 2006


Carterson2 Curious about what you built! TomTom just released TomTomONE which warns driver if vehicle exceeds speed limit. We are actually also developing an upgraded version to this - should we chat?
-- gdc, Jun 20 2007


I like the idea of linking it to cruise control. I never really liked the idea of cruise control until I went to the states recently and found that the freeways there are much safer than ours because everyone is on cruise control and travelling at similar speeds. Much safer than UK motorways which involve constant overtaking and lane swapping. I won't even talk about the autobahn - that's just insane.
-- wagster, Jun 20 2007


Two very small issues:

Firstly, what happens when two roads with different speed limits cross with a bridge? You'd have to make sure the folks on the fast road didn't end up suddenly braking - or those on the slow road suddenly accelerating. Easily solved, but needs taking into account. (This could also occur with two parallel roads with different speed limits, if the GPS wasn't precise enough.)

Secondly, the cruise control needs to be aware of upcoming speed limits and slow you down as you approach them, rather than braking sharply as you enter them.
-- Cosh i Pi, Jun 21 2007


The GPS nav systems must already deal with your first problem, [Cosh]. The second is a good point but again fairly easily solved.
-- TheLightsAreOnBut, Jun 21 2007


//I see no reason for people driving having to look out the window //
Well, of course not, god forbid that drivers should have to look out of their cars when they've got a GPS, an MP3 player and a mobile phone to monitor.
-- AbsintheWithoutLeave, Jun 21 2007


Hey world. Here it is: After market cruise control you can use off-highway. Comments welcomed: gpscruise.com

BTW, halfbake, you need to add email opt-in notification when people post here.... ;-)
-- carterson2, Aug 08 2008


I am also interested in obtaining a data base with speed limits throughout the nation. My company recently built a speed limiting device, but the next step will be to attach a GPS to it and download real-time speed limit data to it to make it a dynamic, automatically controlled speed limiting device. If anyone knows how to get access to speed limit data (in the US) please let me know.
-- jsr27350, Sep 18 2008


I'm assuming that there are some user friendly built in overrides, if you want to sell any of these things.
-- normzone, Sep 18 2008


This is already (almost) baked. I have a Garmin GPS system that has the speed limits on highways and major roads. I honestly don't see the need for it to know the speed limit on smaller roads, generally they are all 30 mph anyway.

To address a comment, if the speed limit changes, even for a few miles, the GPS "knows" and shows the correct speed limit. It's actually kind of fun to watch as you pass the new speed limit sign because it usually changes within a few seconds.

I don't like the idea of the speedometer changing color or the car automatically dropping you down to below the limit if you're on cruise control. The former is just an annoyance and the latter is downright dangerous. I prefer to be in complete control of my car when I'm driving. The only thing I let my car to do by itself is turn on the lights with the little sensor it has.
-- rfl717, Sep 19 2008



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