Concerned Mother,

From the map, it looks like this is a closed-end development. Therefore, these speeders doing "50-60 miles an hour" must be fellow residents, or their visitors.

Take down the license numbers and report them to the police. After a few days of this, they'll probably send someone out to observe for themselves.

Sound like a lot of trouble for you? Hey, it's YOUR daughter that wants to ride her bike. Take some action, don't just gripe on a message board.