I’m going to invite you to answer a series of “pop questions,” a la speedy Keanu Reeve.
Pop question one: How often do tyre blow-outs occur in typical passenger cars? The answer, very rarely. We see blown treads on the highway, but they’re almost always from large trucks.
Pop question number two: how likely is you’ll notice that your tyres are under inflated by 20% or more? Answer, this time: I’d guess that it’s pretty likely – an under inflated type is pretty obvious.
However, it is the unexpected answer to both of these questions that is driving the legislature to mandate TPMS.
Phillip Zaroor, president of PressurePro (a leading TPMS vendor) quotes research showing excess petrol usage due to under inflation in the US is around 16 million litres per day. According to the US Bureau of Transit Statistics, there are around 240,000,000 cars and light-commercial vehicles in USA. This means that each vehicle on average wastes one fifteenth of a litre per day (big deal!).
The SEMA website also quotes The Insurance Institute for Highway Safety suggesting that 200,000 accidents in the US were caused due to blowouts in 2007 (less than 1 per 1150 vehicles).
Herewith we have the sum total of reasons to mandate the use of TPMS on all new vehicles.
Although trivial, this could be a good idea, right? Unfortunately, no.
The problem with TPMS is in the implementation. Specifically in how the pressure sensors communicate with the control unit located close to the driver.
So, if you were designing such a system, how would you communicate the pressure data from the tyres to the central controller, considering you have a design lifetime of at least 7 years and need to keep the costs down?
The designers took a very obvious technology and adapted it to the situation: RFID. This technology is already in use for short-distance reading of passports, transportation ticketing, retail and many other applications. In this instance, there is the extra problem of communication distance – the rear wheels of a truck might be 10m or more from the controller.
One of the side benefits was that innately, RFID uses uniquely serialised chips – no two RFID tags share the same ID number.
Now do you see the problem?
Allow me to explain. Firstly, recall two critical pieces of information – “10m communication distance” and “unique serial numbers.”
We all know that passports can be read from a considerable distance to the detriment of the holder. TPMS is just the same. Let me summarise a few scenarios that have been outlined by a variety of bloggers.
Imagine embedding RFID sensors at regular intervals in the road. Speeders won’t have a chance; neither can they obscure where they’ve been. Unlike GPS, you can’t simply turn it off. And obscuring your number plate won’t help either!
What if a “bad guy” knows your TPMS ID numbers? He suddenly has a much easier time tracking you, or alternately being able to wait for you to go by a particular point. One blogger even offered the possibility of a road-side bomb being triggered by the victim’s own vehicle.
Are the limited benefits (1/15th litre per day) and a slight reduction in accidents (only if you never check your tyre pressure) worth the privacy trade-off?
As they say, may you live in interesting times.