The famed Disney epcot center has fiber optic bundles built into the cement. These are used to razzle-dazzle generations of kids.
The same concept could be used to herd generations of adults through the convoluted streets of everywhere. I propose embedding fiber optic cables in pavement on normal
streets. The fiber optics are laid down in the cement which means the high powered efficient bulb can be located in a convenient box next to the road. alternatively "cat eyes" could be placed over the fiber optic ends so that they don't get damaged.
it could be used for several indications, for example if there was an accident or a lane was shut down, red x's or arrows could appear on the cement almost instantaneously (much like the painted ones now) letting you know to merge. These could change colors with traffic signals letting you know the light has turned yellow if you're stuck behind a massive truck. it could replace signs to let you know about time based rules (no left turns between 2-5 pm, loading zone from 9-5) so instead of a hard to read sign that will give you a ticket, a giant red x appears in the turning lane, or a loading zone appears.
they could also be color coded to indicated road conditions (blue means slippery, yellow means traffic etc) and when an ambulance comes it would flash giant X's and create a lane down the middle of the road for them to drive in.
It could also be used in race tracks instead of flag men, to indicate crashes or spilled oil. instantaneous results and could put up routing lines
Now the final aspect is that using traffic monitoring cameras and light gates. a computer could determine the current capacity and average speed of a car lane. the lane markings could change color to indicate if a lane was less than ideally populated. This would help speed up traffic.