This is why computerized systems that detect vehicles and help those
who are entering and leaving a parking lot are a good thing. Such
systems already do exist. In the Hourly Garage at BWI Airport near
Baltimore, MD, it exists on a couple of levels. However, there are
still some issues with it (shortly after installing it, the airport had
to remove some parking in the garage because it was too close to the
terminal due to post-9/11 issues, but the system still acknowledges
those spots as existing), but as technology progresses, hopefully it
will become cheaper and more common place.