That’s not the way with any intersection I’ve been in and an emergency vehicle went through. They turn their light green and all others red. Makes sense too, that way traffic already waiting for the light ahead of the emergency vehicle isn’t plugging up the intersection.
Off topic, but opticon light changers may change all the signals to red or just certain signals green. This is selectable by the municipality and I have seen both in the Chicago area. I’m told that in virtually (all?) every state, flashing lights are not legal unless used for strictly defined signalling, ie turn signals, hazard flashers, emergency vehicles, towtrucks, etc.
Usually, the ones I have seen have uncolored flood-type bulbs facing each of the lanes. There is a certain order to the floodlights…something like the flood will flash for the lane with the detected strobe while the others have steady-on. This is so that if two ambulances are screaming to the intersection, the one wiht the flashing will have the right of way and the steady will know there’s another emergency vehicle in the area.
And for the buried metal detection loops, I once read in a bicycle magazine to lay the bike down over the loop to turn the signal. Seems the larger metal cross section and closer proximity is often enough to trip the stoplight.
This also works at fast food drive through windows 
IIRC, the ‘Opticon’ operates on a simple 100hz strobe light. Look at the light bars of emergency vehicles in areas that have this system. There is a clear, usually center-mounted strobe light. It shouldn’t be too difficult to measure the frequency of this light (they don’t appear to be modulated) to confirm that they operate at 100hz. There is likely some rule against using a similar strobe light on personal vehicles, but perhaps not. Might help the commute if the local constabulatory forgot to make it illegal!
As far as the OP, I think a ferrite core might very well distort the inductive field sensors at stop light.
I used to work for a contract electronics manufacuturer. We had one customer that was designing a system for traffic lights which would detect the direction of an oncoming siren’s audio signal. Never did find out if the product ever made it past the prototype stage however.
That’s fine for a bicycle, but it’s not going to be much fun picking up a large motorcycle (or replacing any scratched fairings and broken wingmirrors/brake levers) at every traffic light…
Just for you, OP, I asked this dude at work if they work. He rides a Harley.
He say’s he doesn’t have that problem, and “Fuck all you guys anyway. That’s what you get for riding a rice burner.” 
Too Cool, 
huh?
Many of my coworkers ride Harleys too (see Mangeorge’s above post) with no problems, but some lights aren’t triggered by the Sportster model (Harley’s smallest bike). A coworker with a Sportster was told that the ‘light changer’ is simply a largish rare earth magnet. He yanked the magnet out of an ancient SCSI drive (it was a huge drive and a huge magnet) and that seemed to do the trick. Just anecdotal evidence.