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T.RD.M. V.2.6
(Al/2002)
6.3.6.10 Lane drops do complicate enforcement procedures particularly with regard to the general
prohibition for medium and heavy goods vehicles and buses using the fast lane of a three
lane carriageway, as at the point the lane drop starts the carriageway ceases to be regarded as
three lanes. Additionally lane drops particularly can cause difficulty to drivers on the
nearside lane who either have to make a sudden movement to remain on the main line, or to
follow the slip road. Both situations can be the cause of accidents occurring. Therefore
when considering the use of lane drops along Expressways account must be taken: of the
necessity to use gantry signs, and not road side signs; whether the use of a "lane drop" will
create unnecessary difficulties in respect of any future maintenance requirements; and that
all regulations in respect of overtaking, lane prohibitions, and keeping to the left can be
adequately enforced.
6.3.6.11 Junction designs requiring offside slip roads where by the fast lane in effect becomes the
slow lane for vehicles leaving the Expressway should be avoided. Apart from the obvious
dangers such designs can cause because of the necessary weaving involving vehicle
travelling at high speed, it also complicates enforcement in respect of vehicles keeping to
the left and heavier vehicles not being permitted to use the fast lane of a three or more lane
carriageway.
6.3.6.12 At an intersection of two Expressways where a carriageway diverges to form two
carriageways of equal status, it will be necessary for vehicles to weave across lanes and the
notion of having a fast and slow lane in the vicinity of these junctions will generally not
apply. However it is essential that a sufficient weaving length is provided for the
manoeuvres to be carried out safely, and that adequate directional signs in the form of
gantries are provided.
6.3.6.13 Access to Service Areas or Maintenance Operation Centres should be either off the
Expressway by purpose designed grade separated facilities or from the minor road network
adjacent to a grade separated junction, and further advice on this is contained in Section 6.7.
6.3.6.14 Although the general principles in respect of the design of merging and diverging lanes
given in Sections 4.6.8 and 4.6.9 respectively of Chapter 4 of this Volume will apply to
Expressways, the various dimensions regarding merging and diverging lane lengths will not,
as in Sections 4.6.8 and 4.6.9 the dimensions are based on a main line design speed of 100
km/h or less.
6.3.6.15 Diagrams 6.3.6.1 to 6.3.6.7 show the appropriate dimensions and entry and nose taper angles
for Expressway merging and diverging lanes for main line design speeds appropriate to 100
km/h or less.