Vaporware: Road Tunes
Almost everyone has heard the awful sound of the rumble strip along the nation's highways and major roads. Sometimes the roadway itself is grooved to allow for better drainage and safer driving conditions in wet weather. It should be possible to vary the frequency of these patterns in the roadway itself to create sounds only possible to hear clearly when driving the correct speed. If the audio were carefully recorded and processed then spoken advertisements and cautionary messages would be possible.
Since the audio range for human hearing is rather narrow, it is possible to make layered audio where a very fast moving vehicle would hear an audible message to slow down while a very slow moving vehicle would hear a warning to speed up. The fast lanes could have reminders to keep right except to pass, while the slow lanes simply included vocal indications of changes in speed.