Can my car tell me the speed limit?

By: Robert Lamb

Essential Car Gadgets Image Gallery Sure, we have speedometers, but can't something else on the dashboard tell us what the speed limit is? See more pictures of essential car gadgets.

It's easy to fall into a herd mentality out on the open highway. There'­s safety in numbers, protection in conformity. Travel too slow and you'll incur the angry honks of your fellow drivers. Travel too fast and you'll attract unwanted attention from robotic speed cameras and police officers wielding radar guns. Naturally, the best way to avoid flashing blue lights and wallet-busting tickets is to stick to the car speed limit, but what do you do when you don't know it?

It's an easy situation to find yourself in. You take an interstate on-ramp or wind your way through crisscrossing rural roads. The next thing you know, you're wondering if the speed limit is still 65 mph (105 kph) or if you missed a sign somewhere along the way. In many areas, you can always fall back on the standard default speed limit. For instance, in the United States, California's default highway speed limit is 65 mph, making it a good speed to drop back down to if you're in doubt. In addition, just knowing the speed limit isn't always enough. You can earn a speeding ticket for going faster than current weather conditions, such as fog, warrant, even if you're traveling at the posted speed.


At times it seems like law enforcement officers don't even want you to know what the current speed limits are. All of this leads us to the inevitable question: Can't my car tell me what the speed limit happens to be? In an age when GPS devices seem to be replacing roadmaps, is it too much to ask for a built-in speed limit indicator? Wouldn't such an option make the roads safer, in addition to cutting down on driver anxiety?

Read on to find out.


Driving into the Future: Speed Limiters and Intelligent Speed Adaptation

Can you drive 55? Should you? The right GPS device can let you know what the speed limit is at any given time.
Can you drive 55? Should you? The right GPS device can let you know what the speed limit is at any given time.
© Sheasby

While the 21st century hasn't yet delivered on all the science-fiction promises of yesteryear, it has managed to make our driving experience a little more Knight Rider-esque. Global positioning system (GPS) technology tracks our location, vehicles can park themselves and, yes, with the right equipment, you can look down at your dashboard and find out exactly what the speed limit is. Yet tragically, flamethrowers and ejection seats are still not standard issue on most automobiles.

With a GPS receiver and a relatively clear sky, a driver can pinpoint exactly where he or she is on the globe. This is because a GPS gadget receives signals from at least four of 24 orbiting satellites [source: Global Positioning System] The device calculates its distance from these satellites to determine its exact location on Earth. Sync this up with a computerized map, and you suddenly don't have to mess with cumbersome and confusing road atlases anymore. Most service providers keep these maps reasonably up to date with current road, city and location names, although that shouldn't prevent you from downloading updates frequently.


Some GPS applications allow users to program custom speed warnings. These devices are quickly becoming obsolete, however, as many GPS gadgets go the extra mile and actually tell you what the speed limit is on a given road. Sometimes the data are presented next to your current vehicle speed as well, since GPS can determine this, too. Still, the technology is far from perfect. While such a system might prove highly dependable when it comes to major highway speed limits, less-traveled rural roads might throw it for a curve.

For the paranoid speed demons out there, this technology may seem a little scary. As the technology improves and becomes standard, the vehicles of the future will inevitably know how fast they should be going at any given moment. How long until lawmakers connect the dots and create vehicles that can't be driven over the speed limit? Maybe sooner than you think.

In Japan, the new Nissan GT-R already comes equipped with a speed limiter or intelligent speed adaption (ISA) system. Unless you drive the vehicle onto the GPS coordinates for a racetrack, the onboard computer will prevent the vehicle from going faster than 112 mph (180 kph). The feature prevents drivers from reaching insane speeds and limits them to merely life-threatening velocities, but what happens when ISA systems are less lenient? Politicians and safe driving advocates in the United Kingdom continue to push for mandatory ISA systems in vehicles. They insist that the measure would cut down on accidents, congestion and pollution. In 2003 and 2004, researchers at Leeds University carried out experiments involving 20 ISA-enabled vehicles with largely positive results. Critics, however, argue that ISAs would merely create more problems by turning drivers into unobservant zombies.

Will such technological innovations eventually lead to automated highways full of robotic drivers? Many futurists and transportation experts think so. For the time being, however, no machine overlords can force Sammy Hagar to drive 55. But if he wants to, he can buy a GPS gadget to tell him when he should.

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