The traffic light sensors are set off by the metal in the object passing over it

1. The color red of street-lights is chosen because it is associated with blood and danger. The color for "go" used to be clear but when the filters for red-light fell out the light was clear. Furthermore, from the distant, stars and sun's glare were sometimes mistaken for the "go" signal. Green is associated with nature and is calming and was eventually chosen
http://www.myuniversalfacts.com/2005/10/why-are-traffic-lights-red-yellow-and.html
2. The traffic light sensors are set off by the metal in the object passing over it, not weight.
http://answers.yahoo.com/question/index?qid=20061022163125AAcaKke
3. The most covered song of all-time is Eleanor Rigby (The Beatles), it has been covered 131 different times.
http://www.independent.co.uk/arts-entertainment/music/features/the-10-most-covered-songs-1052165.html