Hi echoes. Not really sure what you're asking about as there are many green bus routes! But don't dismiss public buses if you can find a direct route. The fare is a LOT less and many children use them.
My daughter takes the public bus 74 or 75 to KEVIHS as do a few of her friends. One travels all the way from Dudley on the 74 without any hitches. When it snowed though my daughter walked the 3 miles home along the Soho Road. Her friends carried on walking to West Brom bus station. Quite an adventure. Only takes her about 20 minutes on the bus normally and they are very frequent.
Good safe and quite areas along any of the green bus routes.. We are not from Birmingham and we would be moving to Birmingham so we don't mind moving to any area as long as its safe and quiet.
We have not discounted public buses but as it can be seen from my message above we are bit apprehensive about safety of a 11 year old girl travelling on her own.