Aircraft Overhead

It would be naive of me to think airliners don't fly over my town but I've always thought it very rare. The closest international airport is London Luton which is about 40 miles away. In the last week I've seen loads of what look like 737's going overhead. Some appear so high up they are hard to spot and make no noise. Others are much closer and I can hear the engines. One recently was so low if I had a half-decent pair of binoculars I would have been able to read the tail number. Perhaps even see passengers in the windows!

I imagine they are of different height because some will be climbing and other descending but is there a way of finding out the routes and accurately estimating when it will be flying overhead? Or are the/some routes classified?

All commercial aircraft follow recognised airways
Maybe Luton swopped runways because of the weather and thats why you are seeing traffic
Finding airways above your location is a hit and miss affair and I cant find any(mind you I didnt look for too long)

http://flightaware.com/