Odd behaviour from speed limit recognition

[ColinB]

The westbound carriageway at the eastern end of the M3 has an unusual temporary speed limit through the roadworks, it's 55 instead of the 50 that you usually find in such circumstances. It wasn't just one or two rogue signs, they were all like that so clearly that was genuinely the limit. The Jazz did not display that speed limit at all, it just showed "---". Not sure whether that's an issue with the software being unable to read the signs (maybe it's only programmed to look for "likely" numbers and doesn't know what to do with unusual ones ?), or maybe the the display just can't show it.
It was interesting that many drivers didn't seem to believe the 55 signs, and stuck resolutely to 50 !

[ColinS]

I suspect you are correct in that it only recognizes common signs.  The only other one that mine sees is the no overtaking sign.

[richardfrost]

My H-RV consistently misreads a pair of 30 limit signs and displays 120!

[Jocko]

And they want to go to driverless cars!

[andruec]

There's one point along the A55 where it picks up the limit from an adjacent road and shows 40 instead of (/). What does the limiter do in that situation? One minute your rolling along at NSL (70mph) the next thing the car thinks you're way above the speed limit.

[VicW]

Interestingly my speed limit recognition system doesn't have such 'modern' problems.
It's called the 'Mark 1 eyeball'.

Vic.

[ColinB]

There's one point along the A55 where it picks up the limit from an adjacent road and shows 40 instead of (/). What does the limiter do in that situation? One minute your rolling along at NSL (70mph) the next thing the car thinks you're way above the speed limit.

Car behaviour in this situation has been previously reported here:
https://clubjazz.org/forum/index.php?topic=8617.msg44156#msg44156
and in the follow-up comment here:
https://clubjazz.org/forum/index.php?topic=8617.msg44161#msg44161
That's the reason why I don't use the so-called Intelligent Speed Limiter. How would it respond in the situation where a 55 limit isn't being recognised or displayed ? Dunno, didn't try because I didn't want to risk getting points finding out. I prefer to set the "normal" speed limiter manually.

[andruec]

Yikes! Definitely a bad idea to use the limiter then. I assumed it only stopped acceleration not that it actually slowed you down. I've not bothered to look into it myself because I'm annoyingly(*) good about not exceeding the speed limit. I take pride in it. But it is occasionally nice to be able to glance at the dash to confirm the current limit if bushes or parked vehicles have obscured a repeater sign.

(*)It sometimes seems like I'm annoying every other driver on the road by doing it :-/

[Jocko]

It sometimes seems like I'm annoying every other driver on the road by doing it

Snap. I sometimes feel threatened by other motorists by sticking to the posted limit. Especially in 20 mph zones. The thing is, I go my my GPS speedometer, which reads 10% higher than the car's speedo. Imagine if I was sticking to that!

[andruec]

It sometimes seems like I'm annoying every other driver on the road by doing it

Snap. I sometimes feel threatened by other motorists by sticking to the posted limit. Especially in 20 mph zones. The thing is, I go my my GPS speedometer, which reads 10% higher than the car's speedo. Imagine if I was sticking to that!

My speedo reads low but not hugely so. It's going to vary according to how the tyres wear but last month it seemed to be reading 50mph when my sat nav reckoned 48 and 70 was actually 65 so it seems like a non-linear relationship. But I just don't care. No one is going to really notice the difference in journey times unless they are going hundreds of miles along a motorway. For a typical daily commute +/- even 20mph on the open road will be swallowed up at junctions at one or both ends.

My commute is straight out to main road then 9 miles at 50mph (with a mile at 30mph in the middle) then four miles, five roundabouts and a lot of traffic. Sometimes there's an HGV or even a tractor that knocks the 50mph section down to 40mph or even 30mph. It never makes any significant different to my arrival time. The only thing that does is severe congestion (like when the M40 barfs and Banbury's primary egress clogs up)..and the recent roadworks at the roundabout outside our office.

But on the open road nothing seems to have much impact..it's all dwarfed by what happens in the Town.

[VicW]

My satnav says my speedo reads 2mph high when above 40mph otherwise it's accurate.

Even in a county like Lincolnshire there is very little point in rushing about, you will always catch up something going slower than you are and the overtaking opportunities are few and far between.
Maybe that's why the county has one of the highest accident rates in the country. Death rate this year averaging three a month and it's a good year!

Vic.

[Jocko]

I regularly drive through a huge section of Average Speed Cameras, as they build the new Forth Crossing (opening 30th August), and I like to keep as near to the 40 limit as I can. I reckon on 40 + 10%, so try and keep at or just below 44 on the GPS, knowing that average speed drops away very quickly as soon as you fall below by any amount. No real reason. It is just a bit of a challenge. But it only takes a slower car sitting in lane two and it all comes to nought!

[pb82gh3]

I read somewhere the other day that drivers who break speed limits and drive too fast for conditions on average save about 27 seconds per day. I wouldn't mind betting they then spend more than 27 seconds de-stressing.

[Skyrider]

I regularly drive through a huge section of Average Speed Cameras, as they build the new Forth Crossing (opening 30th August), and I like to keep as near to the 40 limit as I can. I reckon on 40 + 10%, so try and keep at or just below 44 on the GPS, knowing that average speed drops away very quickly as soon as you fall below by any amount. No real reason. It is just a bit of a challenge. But it only takes a slower car sitting in lane two and it all comes to nought!

I live near the bridges, my satnav gives an average of 37mph when I go through at cruise control set at 40 mph.

[Jocko]

That's about what I find too.