Flashing warnings - Speed limits - How?

[egomeister]

Not really a SPL question as such but I thought the most knowledge would be here...

How do the signs that monitor speed then flash the speed limit up if you are exceeding it work (or on occasion not...)

They have a couple of these locally and they don't register anything on my radar/laser detector and also don't appear to have sensors in the road like a Truvelo - just curious as to how they work!

[Einion Yrth]

This says radar - different frequency from that which your detector can detect perhaps?

[egomeister]

Interesting that it uses radar - that wasn't the type of installation used around here, they tend to use "semi-permenant" systems fixed to poles. As you say it may be a frequency not supported by my system. Mine covers:

X-Band: 9.90 GHz
Ku-Band: 13.450 GHz
K-Band: 24.125 GHz
K-Band: 24.150 GHz
K-Band: 24.220 GHz
Ka-Band: 33.40 – 36.00 GHz Superior Band
Ka-Band: 34.30 GHz
Ka-Band: 34.36 GHz
Ka-Band: 35.70 GHz
Laser