Step 1: Analyze the meaning of "knocked down".
In this context, \textit{knocked down} means that the men were hit and caused to fall, which is the correct meaning for a person being struck by a speeding car.
Step 2: Evaluate the alternatives.
TURNED DOWN means to reject or refuse something, which doesn't fit the context.
PULLED DOWN refers to forcibly bringing something down, typically in a physical manner, but not in the context of a car striking a person.
BROUGHT DOWN means to cause something to fall or collapse, but it is typically used for objects, not for people being hit by a car.
Step 3: Conclusion.
The sentence is already correct as it stands. \textit{Knocked down} is the appropriate phrase for describing someone being struck by a car.