LIFE is about choices
First of all May God rest Oscar's soul. Those cops were jerks. They should have went after that fat guy who attacked Oscar and started the fight not the innocent ones. However, this thing shows life is about choices.
A---Mother tells them to take the train. She even touches on this at the end. If they would have drove sure they get stuck in a traffic jam here and there but most likely they get home safe.
B---Oscar even tells fiancé/girlfriend that they should just stay home and watch the ball drop on TV. Probably would have been a good idea...stay home as a family and celebrate with little daughter.
C---When the train is about to come to Fruitvale station stop, why did Oscar separate from his girlfriend/fiancé who sat down? I did not get that part. If they stay together this ruckus never happens.
Obviously in these situations they never thought "Lets choose this so we do not die". Obviously some things are beyond control. But to making the above choices in A or B would have been at least less stressful options for sure.