As for Mike’s comment, I would have to agree that PNDs that are not integrated with the car (such as built-in navigation devices found in various cars such as the latest Honda’s) have difficult volume issues. One other example is in an officer’s vehicle. From the voice chatter on the radio, the siren if its on, and the inherent noises found in these cars are high speeds make it difficult to even hear the instructions let alone actually deciphering them.