When The Whistle Blows
As new US legislation is being introduced to curb trains sounding their horns, this programme celebrates that quintessentially American sound - the passing freight train.
Europe doesn't have train horns because we have fences.
But in America, when they built the railways it was still the wild west where cattle were free to roam the wide open plains.
So instead of fences they had train horns to warn people and animals a train is approaching.
Of course over the years the towns and suburbs spread along the tracks.
The people who live close to crossings can hear the horn blasting away day and night.
For some of them it is a wake up call, literally.
So new legislation is being introduced which will limit the frequency and volume of train horn blasts.
This prompted Diane Hope, a British ecologist and environmental scientist living in Arizona, to investigate how the modern freight train horn came to sound the way it does.