Seems to me that a roundabout at the clusterfuck that is the Decarie/de Maisonneuve intersection would be a great solution instead of closing Upper Lachine.
Roundabouts are the safest of all forms of intersection because they eliminate left turns, which are responsible for a high percentage of accidents. Roundabouts are safe for pedestrians and cyclists because cars go slower and can be made to stop more easily to yield. Roundabouts slow traffic down and eliminate the need for lights. They also usually feature an aesthetically attractive feature in the middle.
Read Coolopolis’ suggestion here: http://coolopolis.blogspot.ca/2012/12/montreal-needs-more-roundabouts.html