Speech annunciation from highway surface grooves

Grooves are embedded in the pavement along the shoulders of many interstate highways in the United States to alert straying drivers with a rumbling sound. Using specially encoded grooves, speech can be annunciated instead. A groove pattern was devised that resembles a recorded phrase of human speech. The original recording was filtered to remove high frequency noise and then dynamically compressed into an equal amplitude square wave with variable pulse width. Before committing significant funding to build and test the encoded strip, the phenomenon was empirically modeled using system identification on the sound of an automobile being driven over existing rumble strips. The input was a simple periodic square wave pattern. Then, several phrases from different speakers were encoded into strip signals and used as inputs for the model. A subjective evaluation was performed to determine the most intelligible case. The selected strip was constructed by milling the groove pattern into sheets of aluminum. Tests with a truck found the fidelity of the sound was intelligible and resembled the simulated sound. An U.S. patent application has been filed