Driving on a beltway this morning. Speed limit 55 mph, though no actual sign. A sign comes up saying TRUCK speed 35 mph. The speed limit sign on my car dash goes to 35 mph. Obviously, this Lexus mechanism cannot distinguish between posted CAR speeds and posted TRUCK speeds.Just an interesting observation I thought I’d share.

 

I've wondered how that system works. In California it is common to have 65 MPH or 70 MPH speed limits with frequent signs for trucks posted with a 55 MPH limit. My speed limit on the dash never reflects the 55 MPH truck speed limit.

 

Any part of a system that is erroneous is considered dumb and should be able to be turned off by the user. I would not turn this off but for the newer infotainment system in the 2024 ES and the new RX I was looking at there is a school zone warning on big screen for a school that was torn down 10 years ago and can't be turned off. That is just one of the things that turned me off on the new RX. Sticking with my 2020 ES300h UL for now until forced to change.

 

I think here in the US, the camera will only scan and recognize the standard speed limit sign, regulated by DOT/FHWA
Anything else around it such as time, minimum, maximum, vehicle type etc. won't be read or considered
I bet there are other vehicles can read all of these sign and smart enough to display it on screen, just not Lexus yet
Those app on your phone (Apple Maps, Google Maps, Waze etc.) work much better, they always have up-to-date database, they don't scan anything, they have it saved already.

I do not rely on this feature on the car, always obverse the road.

 

it also says in the owners manual,

Situations in which the display function may not operate properly

When a sign intended for trucks, etc. is detected.

if you have the embedded navigation system, it’ll sometimes take the posted speed limit off the navigation but once it detects a sign it’ll use that speed limit instead. thus there will be a mismatch between the RSA and navigation speed limit.

 

That's exactly what happened.Since this road is 55 unless otherwise posted, the sign it picked up was for truck speed. It changed the next time a speed sign was passed. No problem. Just wanted to make sure mine was functioning as designed. I was using WAZ off my phone and not an embedded nav system which I wouldn't spring for because I use s system through the phone.

 

I've noticed that mine will often take the 20 MPH sign from school zones and use that, even though the sign reads "when flashing". So even at 10pm, it suddenly tells me I should be going 20 MPH instead of the regular 35 or whatever is posted as the normal speed limit.

 

I'm happy that the car is not smarter than me.
Here's another example: whenever I get near a school, even at 10PM on a Saturday, I get a little note in the corner of the screen telling me I just entered a school zone. This does not bother me. Most of my friends think it's nice of the car to mention it, even though the kids are home all tucked into bed.

 

I turned this off first week

 

What makes the car dash speed limit sign turn off when you are still on the same road, just a few miles past where it initially read a sign?
I can't relate it to distance or time, maybe a major change in direction like on a windy road.

 

While it isn't very informative, the Owner's Manual (see page 194 of the 2024 pdf version) has this:
Your guess is as good as mine as to what's in the "etc." bin of road changes and what goes into determining a "certain distance" has been travelled.

 

Thank you for looking it up. It really does seem like a random event, but it would make sense that a change in road direction would flip it off. Around here the cows decided where the roads would be and humans just paved over it.

 

I had a similar thing happen the other day. Same issue. No sign because I went from state road to indian reservation. It saw the 35 posted by the intersection but never change to 55. It was kind of a back road so I could see it.
I thought I saw a training video where if the Lexus navigation had speed limit information via (the cloud) google maps then it could update from that info. I haven't tested it.