Brian Bartlett raises an important point regarding the use of grass lined drainage channels (swales) alongside carriageways and the potential for the bogging down of broken down vehicles in wet weather and damage to the drainage system during vehicle recovery.
One solution is to use an engineered grass surface with load bearing capability such as the Advanced Turf Systems (ATS) involving a selected rootzone layer into which is blended small interlocking polypropylene mesh reinforcing elements.
Grass roots penetrate the mesh to form a deep anchored root system and stable load bearing rootzone. Over very weak formations the system can be further stabilised by placing a conventional sub-base layer below the reinforced rootzone.
ATS has a proven performance in occasional access and emergency service routes and grass verges. It could readily be applied to swales. Clearly there would be an additional cost element in providing this positive support but compared to a conventional pavement these costs are relatively small.
John H Dixon (M), Tensar International, email@example.com