I wish to make some comments on the highway drainage of the A120 Stansted to Braintree Improvement (NCE 24 June).
My concern is over the use of a grass lined drainage channel, called a swale, along the edges of the carriageways.
In principle this has environmental benefit and saves on construction costs.
However, it has a particular disadvantage when used on all-purpose dual carriageways because it takes up most of the verge and, in wet periods, can become extremely soft.
On such carriageways the verge will very likely have to be used by broken down vehicles.
The consequence of this is deep rutting and disruption of the drainage system, plus the possible need for vehicles to be towed out in wet weather.
A two lane all-purpose dual carriageway is the worst situation to use this type of drainage as there is a real pressure on the vehicle in difficulty to leave the carriageway for safety. The most appropriate situation therefore is on motorways with a hard shoulder.
Apart from the A120 I have noticed swales being installed in other dubious circumstances and I wonder if additional advice is needed on the use of this drainage.
Brian Bartlett (M) BartlettBR@aol. com