I don't know where you live but we've had sensors in the pavement at stoplights here for years. With computer chips getting affordable the sensors can determine how long to allow the light to stay green to allow most of the cars in line to make it through.

its nice to know that some countries can afford such innovation, by the way im from the philippines. and yes we dont have that kind of technology yet but i'm hoping that we'll have it too. what country are you from "HYENUF"?

In the US, Canada, and most of the industrialized countries in Europe, most lights do actually have sensors.

The problem is, that they work in a way that most people don't expect. Traffic lights themselves always follow a certain pattern (in most 4-way intersections, there are eight individual phases in the pattern), and the phases have inter relationships that can't be broken without causing accidents. The problem is that jumping around in that pattern causes all sorts of issues (too many to explain here), so, when one of these sensors is activated, what it really does is:

1) If the phase that would allow the car to continue is active, it lengthens the length of the green (but, it usually does so in a dropping-off sort of way, so that nomatter how busy a street is, it will still allow the side streets to cross)2) If it isn't, it will decrease the time for the current phase (usually, in an increasing manner, so if you have tons of traffic on one street, and very little on another, the second's time is reduced signifigantly).

Cross-walk buttons are another issue all together (and I include them here, just because I'm on a roll): Most people think they work like #2 above. However, what they really do, is have a delayed action like #1 -- they make the associated green lights last atleast long enough so that pedestrians can cross before they get run over. The walk/dont walk lights act a bit different, too. The 'walk' signifies that if you were to step off the curb while it is on, you will make it -- thats why it always seems to switch while you're in the middle of the street -- it's only times to allow the average person to get about 10 steps from the curb.

Why have the expense of people with cameras? A networked timer chip could handle all of it (maybe a $10 microcontroller max), and change times based on time of day (i.e. longer lights for busy roads at rush hour). Sensors could be integrated later with a software update when the budget comes through after you save the cash on the people and the cameras.