You, Sam, Steve and Nat were being chased by The Winter Solider, fearing that he was going to kill you all

In reality, The Winter Soldier, aka Bucky Barnes, was actually programmed to protect you! So, he was trying to save you from the other 3, you guys didn't know that

Sam dodged the traffic as The Winter Solider was jumping from car rooftop to rooftop, trying to get to you guys