Since GPSApp routes are pregenerated on a PC, couldn't the TTS program be integrated into the route generation pipeline to precompute the spoken directions? Would mean a longer conversion process, but would be doable.

Edit:The process would be to use the TTS program to compute the names of roads, seperate from 'turn', 'exit', 'continue', 'left', 'right', 'onto', etc, to allow it to determine what the real turn would be at runtime (coming from the wrong direction etc..).