Yes, in places in which there are high incidence of car bombings, barricades should be placed around a building. In countries such as the United States where gun violence is the prevalent crime, this measure is not necessary. However, in countries in which car bombing attacks happen at a substantial rate this protective measure should be used.
Barricades around public buildings to prevent car bombings might work but if someone wants to blow up a building they will more than likely find a way. There are a lot of preventive measures that you could implement but a lot of times those could be blown up too. Bombers will always find a way.
More needs to be done to ferret out terror risks, without giving up our basic civil rights. Terrorists are bullies and wish to disrupt our social order in the name of some esoteric utopia they will never see. Giving in to terrorism is like handing over your lunch money to the school bully instead of kicking his butt.
No, public buildings should not be made inaccessible to car bomb attacks because there are good things that come from cars being able to access buildings. Celebrities and politicians are safer when they travel if they can travel directly into a building by car. Some people have luggage and a lot of things to carry.