On more mindless forms of transport try the 10-minute 'body scan’: “Take a breath in and focus on the sensation – the air rushing through your nose, your chest rising – then breathe out. Let your mind travel all around your body, feeling every movement and concentrating on the present. If a thought comes to mind, acknowledge it, but – like a passing cloud – let it drift off again.” As your breathing slows, your blood pressure will drop and muscles naturally relax.
Reference: Daily Telegraph