How do Ottawa intersections get selected for advance left-turn arrows?

A dramatic scene unfolded at the Fallowfield Train Station on Sunday afternoon, as a car-train collision triggered a massive response from local paramedics. Firefighters rescued the driver of the car, who was trapped inside the mangled vehicle and was pushed dozens of feet into a bush. She was then taken to hospital with non-life threatening injuries and remains in stable condition. Dr. Lesley Spencer, who used to work as an E.R. doctor in Smiths Falls, was waiting at the train station for her husband to arrive. She recounts what she saw on Ottawa Now.