I've just done that. My score is 31 and has an amber label to it.
BUT - I live in the country in Suffolk, 4 miles from the nearest town and on a B road that gets a medium/light traffic flow. So, either this programme is so sensitive that its picking up some local farting pigs or its accuracy needs to be questioned.
Same where I am, proper countryside but it's imperial college London... Oh wait... It's imperial college London, the accuracy definitely needs to be questioned