News0 min ago
pollution control valve
when driving on the m25 i have noticed signs for pollution control valve on the side of the hard shoulder (permanent signs not temporary) what is this and what is it used for ? i know obviously pollution this entrigues me as i have not seen these signs on any other motorway except the m25
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These are mainly on the south side of the M25, but they are in a few other places as well. By the motorway, usually when you are on an embankment, there is a larger than normal ditch called a balancing tank (although it is just a big ditch). These 'tanks' are used to regulate drainage run off during rain, as the water course the rain drains into may not be able to take all the water at once, so it prevents local flooding. As a consequence of this, if an accident happened on the motorway, say with a petrol tanker or just a ruptured fuel tank, the liquid will find its way into the water course via the balancing tank. By putting a penstock (which is just a flash word for a big valve) on the exit of the tank, you can use the tank to hold the pollutant until it can be safely tankered away. This system is used on newer and recently re built roads. On old roads, the council just chuck a load of sandbags in the ditch to dam it up and hope the ditch will be big enough to hold all the polutant.