The 9/11/01 terrorist attacks upon American soil were a seminal point in American history, to which, to a certain degree, time is now, measured pre-9/11 and post-9/11. There have been numerous government agencies created specifically because of 9/11, such as Homeland Security, metadata mining implemented on a national scale, border fence improvements as well as new immigration identification processing and reform, significant changes to airport security rules and so forth since the advent of 9/11. Still, despite all of these changes, of which some are definitely noteworthy material changes, there hasn't been any additional checkpoints setup within America or added to America, since 9/11. This means that residents of America can pretty much walk and drive to whatever destination that they are going to without having to go through annoying security checkpoints.
The fact that security checkpoints have not been added into strategic areas within America is, to a certain degree, somewhat surprising, as there isn't much of anything that is more conducive to population and crowd control than the setup of checkpoints. The thing about checkpoints is that it places all residents going through a checkpoint on public roadways and property, on the defensive, as they recognize that having contraband or not having the correct appearance or proper respect to these authorities could result in harassment or much worst. Then too there is something to be said for having the ability to setup random checkpoints or to stop and frisk any citizen that is out in public, with or without justification, in the sense that by having such an ability, it allows the State to better control its population while adding in the all important fear factor for those that are desiring to mess with America.
However, there are two basic problems with adding additional feet on the ground for security and checkpoints within America, to which the first is obviously, that those that are innocent, good citizens, and so forth, will find it a real hassle, a time waster, and almost an affront to them personally, each and every time that they are stopped by homeland security personnel or at a checkpoint. The second problem is even greater, which relates to the fact that in America, this is not supposed to be a police state, in fact, there is a presumption that unless upon probable cause that police and other agencies do not have the Constitutional right to stop and harass citizens.
The thing about checkpoints is that they are a security measure, which may or may not be effective in what they are set up to actually do; what cannot be denied though, is that security checkpoints in the absence of a real and present danger, are in direct conflict with the God-given right for citizens of the United States to enjoy their life, have liberty, and be able to pursue their own version of happiness.
The 9/11 terrorist attack has made material changes to America, it has not added, however, additional checkpoints within America, which is a blessing, because the thing about Governmental authority, is that they are forever coming up with hobgoblins to keep the population clamoring for more protection and more security, with far too many not recognizing that by their panic in attitude and mindset, they are forging the very chains of their own new serfdom or slavery.