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T.PD.M.V.2.3
(Al/2001)
33 Road Alignment
33.1 General Principles
3.3.1.1 When designing a new road or improving an existing road, the alignment should be selected
with care so as to:
(i)
(ii)
Minimise any detrimental effects that may be caused by noise or fumes on the
surrounding environment.
Ensure that communities are not unnecessarily severed or cross movements unduly
restricted.
3.3.1.2 On dual carriageway roads, the alignment should aim to provide at least the minimum
standards defined in the following Sections. In addition, the following principles should be
followed wherever practicable to secure a satisfactory alignment.
(i)
(ii)
Horizontal and vertical curves should be as large as possible.
Changes in horizontal and vertical alignment should be phased to coincide
particularly on high speed roads. Where this is not possible, one curve, usually the
horizontal curve, should embrace the other.
3.3.1.3 Rural locations and urban locations are those areas where the Road Types referred to in
Section 3.2 occur. Generally therefore, Hong Kong Island, Kowloon and new towns will
have urban locations, and the New Territories outside of new towns will have rural
locations.
3.3.1.4 Whilst the Design Speed derived minimum geometry as detailed in the following Sections is
equally relevant to single carriageway design, the additional dimension of opposing vehicles
means that the various geometric parameters must, for rural roads, be assembled with much
greater care than the simple aesthetic design considerations described in paragraph 3.3.1.2,
that is:
(i)
(ii)
(iii)
For the improvement of existing rural single carriageways, evidence of operational
problems always exist. Sharp bends and junctions causing congestion or accidents
can be identified for improvement; hill sections causing congestion can be identified
for the provision of passing bays or climbing lanes. Proposals for improvement
should concentrate on those features with evident problems, and not on bringing the
entire alignment "up to standard".
The design of significant lengths of new rural single carriageway roads, however, (in
excess of 3-4 km), creates a real problem for the designer to ensure that the design
will appear to the driver to be a conventional single carriageway, and not a high speed
route. The alignment recommendations for dual carriageways shown in 3.3.1.2, are
not appropriate for single carriageways. Great care should be taken in selecting the
alignment, and mid to large radius curves should be avoided in favour of straight, with
short, low radius curves to facilitate changes of horizontal and vertical alignment.
Such curves shall be accompanied by conventional double white line road markings
and signs to prevent overtaking at these points. Climbing lanes should be provided on
gradients to ensure regular opportunities for passing slow moving vehicles.
In urban locations, the frequency of junctions, traffic signals, etc., and low operating
speeds means that no special consideration need be paid to design, beyond normal
Design Speed geometric requirements.