Subject: How do those lines under the pavement at traffic lights control the lights?

At intersections with traffic lights there are usually metal 
lines under/at the surface/imbedded(?) in the pavement where cars 
stop at the light.  I think they somehow detect if a car is 
stopped there, and therefore, time the light somehow.  At a newly 
built road I have seen multiple lines radiating out from the 
curb, crossing all lanes, including the left turn lane.  How do 
they work and how do they "install" the system after the road is 
built?
Thank you for responding. 

Re: How do those lines under the pavement at traffic lights control the lights?