You must ban cars. See how dangerous they are.
And no way a gun could have stopped it.
But maybe another car 
No, not in this case.
The man used his car as a high velocity weapon. Full speed racing through the crowds, to bypass security I guess. Thus getting access to a secluded piece of road where a kind of parade was going on. All casualties are audience, that he overran full speed from the back.
No car could have stopped him, unless killing even more of the audience.
You see: with better access to guns, he could have gotten a rifle and shot directly at the royal family, who probably were his presumpted victims. Now a lot of innocent bystanders were killed for nothing. No innocent bystander was ever shot when someone murdered or trying to murder US presidents.
Sorry, but that's just not true.
When Giuseppe Zangara attempted to assassinate United States President-elect Franklin Delano Roosevelt, Roosevelt was not injured, but five people were shot: Margaret Kruis, Newark showgirl; William Sinnott, an oldtime New York City detective who used to guard Governor Roosevelt; Russell Caldwell, Coconut Grove youth; Mrs. Joseph Gill, wife of the President of Florida Power and Light; and Chicago mayor Anton Cermak, who died of peritonitis nineteen days later.
When Lee Harvey Oswald assassinated John F. Kennedy with a high powered rifle, the governor of Texas, John Connally, was also shot in the back, chest, wrist and thigh. Another innocent bystander, James Tague, was wounded in his cheek by a bullet or bullet fragment.
When John Hinckley, Jr. tried to kill Ronald Reagan, he wounded three other men, White House Press Secretary James Brady, Secret Service agent Tim McCarthy, and D.C. police officer Thomas Delahanty. They all survived, but James Brady was permanently disabled.
