The gully, its connection pipe and the length of gutter that carries water to it. Water enters through the kerb face continuously along the run instead of travelling to discrete points.

That removes a set of things that fail: gully pots that silt up, connections that settle and crack, and covers that are struck by traffic. Each was a separate maintenance liability in the running surface.

It also removes the ponding that develops around a gully as a road surface deforms, because there is no single low point the whole gutter has to reach.

In most conditions yes, because water leaves the carriageway close to where it lands rather than running along the channel line to find an inlet.

The practical benefit is less standing water at the kerb line and less spray, which matters on high-speed roads and on any surface where the gutter is also a cycle lane.

The limit is the inlet area itself. Openings in the kerb face are finite, and on a very steep gradient fast-moving water can run past them, which is addressed with larger or more frequent openings rather than a deeper unit.

By jetting from access units set along the run at planned spacings, in the same way as any concealed channel. Those units are part of the layout rather than an addition.

The inlet openings themselves need periodic clearing, since they collect leaf litter and road detritus at the kerb line where sweeping tends to push it.

Access spacing is set by jetting reach and by the site's maintenance regime. A trunk road with regular planned cleaning can accept wider spacing than an urban street cleaned reactively.

Carriageway duty, and the higher classes are usual because the unit forms part of the road edge and is struck by wheels mounting the kerb.

The kerb face takes impact as well as vertical load, which is a different demand from a channel in the middle of a surface, so the units are substantial and the bedding detail is part of the rating.

Where buses and heavy goods vehicles routinely track close to the kerb, at stops and on tight radii, the specification is raised accordingly rather than averaged across the scheme.

Yes, and it is a common resurfacing improvement, though it is a kerb line replacement rather than a drainage addition. The existing kerbs come out and the units go in on a prepared bed.

The connection to the existing system is the part that needs thought. The run has to discharge somewhere, and reusing the old gully connections as outfall points is often the economical route.

Levels are the usual constraint. The units are deeper than a standard kerb, so there must be room below the kerb line, clear of services, which is checked before the scheme is priced.