Where the barrier is to be constructed in an urban area or as a walkway or roadway, kerbs
of timber, concrete or other suitable material may be placed at the edges of the backfilled
trench to support more rigid covers which are able to withstand traffic loading. Alternatively
a box structures, of a form similar to a polymer crate, may be placed in the trench (Figure 3)
to provide stability and support the covers in the event of traffic or other loading when the
barrier is not in use.