evidence from the investigation indicated that longer yellow lights actually reduce the number of accidents at busy intersections. The only problem is, long yellows also have a negative impact on revenue,
http://www.freerepublic.com/focus/f-news/2001566/posts
ht Disambiguator
I have heard that people get used to the long yellows after a while and adjust their behavior so there is no improvement in accident rates. Whether this is true or not, it is CERTAINLY true that if you delay the green, accident levels are permanently lowered.