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While using Distronic Plus in my 2021 GLC during a recent road trip I encountered a major flaw in speed control. It seems that the state of Georgia has placed signs reading "MINIMUM SPEED 40" signs alongside I75. The signs are identical in size and coloring to their speed limit signs. Unfortunately Mercedes Distronic does not actually read the words on the sign and automatically drops the Distronic speed control from the speed limit (70 for example) to 40 mph. This created more than a few panic moments when the drop in speed ocurred while in heavy traffic. Once I figured out what was happening I turned off the automatic speed control option while in Georgia. I view this as a major safety issue and will be reporting it to both Mercedes and the NHTSA.
Last edited by jj31234; Jun 16, 2022 at 09:49 AM.
Reason: Provide more accurate feature name
The Minimum Speed sign is a standard sign in the US. I don't see it often here, and I don't recall if my car reads it correctly. I do have the automatic speed limit adoption turned off in my C63, though. I don't find it useful in the USA. However, I had it active in Europe during my European Delivery trip, and it worked well. In parts of the German Autobahn there is a speed limit or a lower speed limit when the roads are wet, and it always correctly interpreted that sign. That's not to say that there isn't possibly a bug with US signs, but the system is capable of reading the words. The only issue I had with it in Europe were the lorries. By law they have to have a sticker on the back that looks like a small speed limit sign with the maximum allowed speed on it. Typically 80 kph, so whenever I came close to one it adopted the 80 kph.
Appreciate the find and glad it didn't cause you any traffic issues. I generally have mine turned off all of the time as well.
After reading the manual, that’s the first thing I turned off when my car arrived. Minimum, bus limits. It reads them all. I had an Acura loaner, it read road signs. It showed a 31 mph speed limit after passing a road sign. The limit was actually 70.
Wow, this is an amplified version of my gripe with the street signs. I don't have Distronic, but my 2020 reads street signs and shows the Speed Limit in the instrument cluster and the navigation screen. I've had numerous issues where the Speed Limit indicator is flashing 20 or 25MPH on my instrument cluster while on 55MPH or 65MPH highways. Sometimes it's when I enter the highway (and there is no new speed limit upon entering), and sometimes it's reading the speed limit sign from an off-ramp that I drove past.
If the car slowed to those speeds, I'd be beside myself in anger (assuming I didn't get rear-ended first) My wife's Dodge Durango has a Speed Limit indictor on the GPS screen and it seems to always be accurate (other than construction zones, etc.). Why does Mercedes (and BMW) just overcomplicate things?
I'm likely to vote with my wallet and not lease another MB (the GLC is, I think Mercedes #6) as a result of all of the tech issues (stupid routing, incorrect speed limit indicators, the vaporware of Wireless CarPlay for MBUX that was promised via software update, etc.)
What is this feature called? I want to turn it off...
Its called traffic Sign Assist.
Multimedia system:
4 Vehicle 5 k Assistance 5 Traffic Sign Assist
Activating or deactivating automatic adop‐ tion of speed limits
# Select Limit Adoption.
# Activate O or deactivate a the function. The speed limits detected by Traffic Sign Assist are automatically adopted by Active Distance Assist DISTRONIC.
Displaying detected traffic signs in the media display
# Select Display in COMAND.
# Activate O or deactivate a the function.
% If one of the following systems is activated, the detected speed can be manually adopted as the speed limit:
R ActiveDistanceAssistDISTRONIC R Cruisecontrol
Further information (/ page 162).
Its called traffic Sign Assist.
Multimedia system:
4 Vehicle 5 k Assistance 5 Traffic Sign Assist
Activating or deactivating automatic adop‐ tion of speed limits
# Select Limit Adoption.
# Activate O or deactivate a the function. The speed limits detected by Traffic Sign Assist are automatically adopted by Active Distance Assist DISTRONIC.
Displaying detected traffic signs in the media display
# Select Display in COMAND.
# Activate O or deactivate a the function.
% If one of the following systems is activated, the detected speed can be manually adopted as the speed limit:
R ActiveDistanceAssistDISTRONIC R Cruisecontrol
Further information (/ page 162).
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