A form of design used to encourage slower traffic and to provide better (usually wider) pavement facilities for pedestrians, and indeed cycling infrastructure. While in principle a good idea - narrower carriageways tend to lower vehicle speeds - they must be carefully implemented to ensure that there is not conflict between cycles and motor traffic.
In particular, where carriageway narrowing is employed without separate cycling provision, these kinds of designs tend to force people cycling into the main flow of traffic, which is subjectively unpleasant; or they encourage dangerously close overtakes when people cycle to the left of the carriageway.
On streets with motor traffic levels above 2000 PCU/day, cycling should be physically separated from motor traffic. If this cannot be achieved, motor traffic levels should be reduced, so that the carriageway is suitable for sharing.
Above is an example of a narrow carriageway (2.8m lanes in each direction), with separate cycling provision.