I suspect they were referring to the way that street lighting including traffic lights can be on a different circuit to the housing/buildings, so you can have power to the shops and houses but the street lights might be out.
There are also some instances (I think London has it) where Traffic lights might have the option to be controlled centrally (useful in cities), and so failure of power away from the lights can affect their functions so they may not operate as smoothly as normal.
When our town had issues with the power at peak time (who knew massively increasing the size of the town without increasing the links to the grid could affect reliability), it was interesting to note how and where things went down when there was a power cut.
For example street/traffic lights might be the only things working in a street that was dark, or half the highstreet would lose power along with a load of street lights in surrounding streets (but the houses might still have power).
Oddly enough traffic flowed better without the traffic lights