The battery on my current car which has stop/start is certainly a damn sight more expensive, as I found when it needed replacing in the spring.
As tyres wear, the speedometer will over-read more, but not by much. In practice, speedometer accuracy is not checked during an MOT test. Prosecutions for under-reading may have occured, but I can't find any. Far more likely to collect speeding fines.
I recently drove my work pool car for the first time. At one point the dashboard screen said the speed limit was 70, but the (built in) sat nav screen said the limit was 60....
Yes, this is a really serious prospect. Some slip roads have a 30 limit and in London there are 50mph dual carriageways which run parallel to 20mph local roads.
Theer is the A168 which runs parralel to the M1 btween Wetherby and Scotch corner. Not dual carriageway so 60 national speed limit applies. Can satnav tell if a car is on A168 or M1? Reliably?
learned summat today! dont get over there much.
It seems that all these potential GPS issues are being considered only in the situation where every driver drives with their foot flat on the floor relying on the speed limiters to protect them from both prosecution and being involved in any collision.
I am not sure why you imagine that driving at the legal limit involves having your "foot flat on the floor". I have seen collisions narrowly avoided when traffic is driving at 40 in a 40 limit and one numpty panics on seeing a camera and slams the brakes on. That was only a 10mph drop, if a "smart limiter" suddenly and incorrectly picks up the wrong limit on a national speed limit road the difference could be 40 or 50 mph. To avoid a collision if that sort of braking occurs without warning you need to be totally focussed on the car in front. In practice a good part of your attention is on the cars ahead of that one to anticipate anything that will cause him to brake.
If that happens (and I agree that it's a possibility in the short term and a near certainty in the long term), I suspect that car speed limiters not working will be one of society's smaller concerns...
I didn't say that driving at the legal limit involves having a foo flat to the floor. What I was referring to was that in situations where there are absolute limiters, (in this case a speed limiter) drivers know that it will usually prevent them exceeding that speed so the limiter takes the place of the accelerator and the pedal functionally becomes a go/stop switch, i.e. the risk of speeding is normalised because of the limiter, that is, until it malfunctions.
I make extensive use of cruise control as my driving is mostly long distance on motorways. My own car being older does not have adaptive cruise control; however having driven cars which do I totally get the advantages. I also see great benefits in driver controlled speed limiters, particularly in EVs where "every little helps" in preserving range. Furthermore I drive using Waze as a guide to hazards ahead which has the advantage of providing a GPS indication of speed in addition to the indicated reading of the speedometer so I never consciously go over the limit. Where I have reservations is in having the car decide it knows 100% better than my judgement in 100% of situations.
Yes. My Toyota under reads by 3mph on standard tyres and 2mph on winter tyres
This point about the braking issue keeps being made, one thing which will not happen is cars dropping anchors to get down to speed limits, it is obvious to all that that would be very dangerous and no one is stupid enough to introduce that.
All the cars with built-in GPS I have owned included inertial guidance. They will quite happily keep track through long Alpine tunnels.
I agree inertial guidance can achieve this although they are prone to drift. Most use other inputs such as axle probes and GPS signals to constantly compensate for drift.
Agreed that inertial guidance will drift. In cars, it is definitely a backup to GPS. It should easily last long enough for any of the scenarios suggested in this thread though. I once had the car antenna fail while in Austria, so no GPS signal on the way home. Between interial guidance and 'must be following a road' logic, the system hung on remarkably well, but eventually ended up circling a field in Belgium.
One of the motoring TV shows did a test. If I recall correctly, they put a litre of fuel into two identical cars then drove along a pre determined route around Birmingham. The car that cut the engine at red lights went quite a bit further before it ran out.
Many times that I've driven on motorways, I've encountered a lorry that's taken several miles to overtake another one, clogging things up somewhat, with all faster traffic (that is, all motors, most vans) squeezed into the overtaking lane. There was on, I think, the Newsthump a spoof tale of a lorry driver given a prize for taking from Junction 5 to Junction 19 on the M1 to overtake another lorry; a bit of an exaggeration, but it seems almost that long when you're stuck behind overtaking lorries.
There's a motor near my house with a big sticker that apologises for the slow speed and explains that this is because the motor is fitted with a black box.
