When you first hear these you mistake them for the sounds of frustration. But you soon notice the signs on the back of the lorries asking other road users to toot and realise that something else is going on.
In fact all this noise gives the drivers another dimension to track the traffic in – a kind of 360 degree view.
It strikes me that Twitter is providing the same kind of functionality online. Twitter gives us a continuous sense of where our friends, family and colleagues are and what they are doing – and this is something which is genuinely different and might account at least in part for some of its popularity. Whatever comes after Twitter, something will have to perform this task in the future.