Question:  I travel the same route to work on the same streets and at approximately at the same time 5 days a week. So here it is a holiday week and yes, traffic is lighter but then that gets me into work earlier. Why is it sometimes left-hand signals will be quick and other times they TAKE FOREVER. Is it lighter traffic not triggering the signal or is it time of day?

Answer:  The easy part of your question is the very last.  A traffic signal detector, with very few exceptions, is binary.  Yes, or no.  There is someone waiting or not.  It can not tell if there is one car waiting or several. 

What is probably happening when you want to make a left turn move is that the light is actually taking the same time to respond as usual, but since traffic is so light on the through moves during the holidays it feels longer.  Speaking for myself, I don’t mind waiting a while for my green light as long as plenty of other cars are moving.  But I hate waiting (and it seems like a super long wait) when there is a green on another move but no traffic.