Don’t go and tailgate any buses between Bath and Bristol Airport. You do not want to get too close to their exhaust fumes because it runs on poo. Food waste and human poo! Does it need a coffee to get it to move in the morning?
It runs on biomethane that is produced in a local sewage treatment works and the 40-seater bus has been referred to as “The Number 2!” It can travel nearly 200 miles on a damn good
dump fill up from about 5 people. Link
Now if you had all the crap from out of these 5 it would probably go nearer 500 miles!