GPS speed limiters in action

Imagine a satellite navigation system that not only told you were you were but also made sure you kept within the speed limit.

The New South Wales Centre for Road Safety recently implemented an Intelligent Speed Adaptation (ISA) project designed to control the speed of vehicles using GPS satellites and a digital map of speed limits.

Covering 2500km of road across the Illawarra region south of Sydney where road types vary significantly, the project will use 100 fleet vehicles fitted with the ISA devices, from businesses within the area.

How they work

Two different ISA systems are being tested - advisory and supportive. Advisory systems alert the driver with a sound or a message when the vehicle exceeds the legal limit. Supportive systems limit the fuel to the engine once the driver reaches the speed limit. Supportive systems can be overridden by the driver.

Data recorders within the devices themselves, as well as written surveys will gather information regarding speed limit compliance, traffic infringement rates, fuel consumption, greenhouse gas emissions, driver acceptance, crash involvement and device reliability and usability.

The major aim of the project is to save lives and prevent injuries on NSW roads.

Testing the systems

Project Manager of the ISA project, John Wall invited carsguide for an exclusive test of the devices in one of the Sydney areas that has already been mapped, so we could find out if what sounds great on paper is as good in practice.

Both systems, attached to the dash, looked a lot like current external GPS satellite navigation systems, although as popularity increases they are likely to be integrated.

The system displays are designed to be simple so as not to divert the attention of the driver. The current speed limit within a red circle is just about all you can see on the screen.

If you do not exceed the speed limit, all other alerts are audible, usually by way of a ‘dong’ followed by a voice that lets the driver know when a new speed limit is in place.

Advisory system

“The advisory system is simply a smarter version of a speed limiter that can be found in most modern cars today.” says Wall. “The difference is that with ISA devices, there is no need to manually enter your desired speed limit - the system does it for you”.

Once the speed limit has been exceeded, an initial ‘beep’ is sounded, followed by a voice that lets you know that you are travelling too fast. If you keep speeding the beeps become more frequent until you slow down to the required limit.

Different manufacturers of these ISA systems will carry slightly different alert sounds and warning messages. This particular model alerted us when we were travelling through a school zone which was helpful.

Supportive system

Unlike advisory systems which just advise you that you are speeding, supportive systems actually cut the flow of fuel to the car if you travel over the speed limit.

Initially we were a little apprehensive about trying this one because we like to be fully in control of the vehicle – and are pretty sure we’re not alone in that. But we pressed on,  accelerating hard to push past the 50km speed limit on a straight stretch of road.

The car travelled to about 54km/h and the device beeped before we felt a subtle –  very subtle – loss of power. There was no sudden jolt or jerk – it was almost like the feeling you get when you hit top speed in a golf cart and the limiter cuts in – very smooth and gentle.

Wall explains that “..the system tricks the vehicle into thinking that you have taken your foot off the accelerator”.

A foot continuing to press on the throttle simply held the speed at 54 for a short while, then it dropped to 53, 52, 51 and 50.

Like cruise control in most cars today, gravity and inertia play a part in how fast the vehicle travels. At the moment, the ISA devices do not use the braking systems in the car which is the reason for it creeping up a few kilometres over 50km/h.

The delay can also be attributed to the time it takes the devices to retrieve new data from the satellites and then to perform the complex calculations necessary.

To over-ride the system you simply press the accelerator to about three quarters of the way down to the floor. Once the point of resistance is met, the system cuts out and the car continues to accelerate.

How they went

After our initial scepticism, we were very impressed with the both of these systems. There are so many instances where we inadvertently lose concentration and end up over the speed limit without knowing it. The accuracy of the ISA devices was near perfect and the gentle loss of power when using the supportive system felt very safe and unobtrusive. The audible alerts – unless we were speeding – were helpful rather than irritating.

The ISA devices are simply there as a guide. For those of who remain cynical, remember that both systems can be overridden so the driver is still ultimately in control.

On the drawing board for phase two of the project are devices that will adjust speed limits in rain or fog and even slow the car down – using the cars brakes – within advisory speed limits around sharp corners.

There is no doubt that as the use of more sophisticated technology develops these systems further, there is huge potential for them to advise and support drivers on a much larger scale.

The ISA systems should be commercially available before the end of the trial in November 2009 – when results of the project will be presented. They should cost around $400 – $800.