A few years ago I saw a parking system in Switzerland that made me wonder why the same system hadn't been implemented everywhere. It's so simple - in a multi-storey parking structure, each parking bay has a sensor mounted above it that can tell if a vehicle is parked there or not. If there is, the sensor shows a red LED. If not, it shows green. The result is that you can tell - just from looking at the ceiling, exactly where all the open spots are in a long row of parked cars. It prevents (or should) the long, slow crawl of procrastinating drivers trying to find a space. In theory, you just look for the green lights, and head for those parking bays.
I finally saw my first one of these systems installed here in the US this weekend. The parking garage at the Mandalay Bay in Vegas has this system installed and it works beautifully. The open spots are super easy to spot and the system there also has digital counters at all the intersections that tell you exactly how many open spots there are in any given direction.
Now - this does rely on drivers having some common sense, and I you could tell those who got the system straight away, and those who thought all the red and green lights were Christmas decorations. Several times, we were stuck behind people crawling along, doing the old hunt-and-peck routine instead of looking at the lights. But other times we found ourselves in a fast-moving stream of traffic that were just heading directly for all the open spots without any fuss.
Personally I think this system is genius and should be installed by default in any parking structure. Click the image below to see a larger version where you can see the three open spots.