At intersections where the left turn traffic signals are structured with the Marblelite Doghouse structured left turn traffic signals as well as the 5-Signal Inline structured left turn signals, it is relatively unsafe to make left turns. The part that makes it unsafe is that it may cause yellow trap problems, the yellow trap problem is when the controller decides to give the opposing direction another opportunity to make the protected left turn, the thru signal in your direction will turn from yellow to red, causing motorists the confusion as to the fact that even though their thru signal changed, the opposing direction's thru signal is still a green light. These signals need to be replaced with either the standard left turn traffic signals or the left turn traffic signals that includes the flashing yellow arrow, this way it will solve several issues that arise with the confusion to causing the yellow trap. Also to note, the left turn traffic signals that replaces these left turn doghouse signals or the 5-Signal inline left turn signals need to be all arrows.
For those not sure how the flashing yellow arrow traffic signal is defined, here are some links to the videos that explains the flashing yellow arrow left turn signal:
http://www.youtube.com/watch?v=9nIBGGfkluM
http://www.youtube.com/watch?v=fmvn0rH253A
Also, a link to the yellow trap animation could also be found here:
http://projects.kittelson.com/pplt/LearnAbout/Learn3.htm
