It is my understanding that while traffic signals are almost always hardwired to mains supply (somewhat surprising observation is that traffic cameras often are not but use Pb battery packs that are recharged during the night from street lighting power) they very often use radio interfaces for communication, be it something PACTOR-like, point-to-point 802.11 on unusual frequency bands (ie. sub-GHz) or straight 802.11.
The sub-GHz 802.11 seems to be uniquely american thing. And maybe just pushing anything over RF is somewhat uniquely Czech thing (caused by the fact, that Czech spectrum allocation has somewhat unique additional 10GHz ISM band), but in Prague there is an giant nest of smallish microwave antennas on every tenth street light pole (the extreme is probably Malostranske namesti, where there is 10GHz link between two traffic signals that spans about 70m).
The sub-GHz 802.11 seems to be uniquely american thing. And maybe just pushing anything over RF is somewhat uniquely Czech thing (caused by the fact, that Czech spectrum allocation has somewhat unique additional 10GHz ISM band), but in Prague there is an giant nest of smallish microwave antennas on every tenth street light pole (the extreme is probably Malostranske namesti, where there is 10GHz link between two traffic signals that spans about 70m).