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T.P.D.M.V.2.3
(Al/2001)
33.8 Climbing lanes for Single Carriageway Roads
3.3.8.1 Gradients can cause severe congestion on single carriageways, where a slow moving goods
vehicle will create long platoons of traffic if faster vehicles are unable to overtake. These
platoons will frequently be unable to dissipate for a considerable distance, as overtaking is a
difficult and hazardous manoeuvre on a 2 lane road.
3.3.8.2 When improving an existing single carriageway road, such congested locations will be
readily identified. Significant improvements in flow will be effected by the strategic
provision of climbing lanes at frequent intervals on gradients to permit overtaking where it
is most necessary. It is not suitable to provide gradient/traffic criteria for the provision of
climbing lanes on single carriageways. Each site must be considered individually in relation
to overtaking possibilities on the route as a whole, to arrive at the most suitable means of
achieving improvements to traffic flow. In some cases, the provision of a climbing lane on a
2-3% gradient may represent the most advantageous means of ensuring that steady progress
can be made.
As an interim measure, the construction of strategically located passing bays should be
considered where it is likely that a full climbing lane could not be achieved for some period
of time, and the length of the road in question is greater than 500m.
3.3.8.3 For new single carriageway rural roads the provision of climbing lanes on hills offers the
most economic and effective means of ensuring that there are frequent opportunities for
overtaking and the strategic placing of climbing lanes will ensure steady progress. As with
existing single carriageway roads, it is not possible to provide gradient/traffic criteria and
each site must be considered on its merits in relation to overtaking opportunities on the route
as a whole.
3.3.8.4 The minimum carriageway width at climbing lanes should be 10m, divided into 3 lanes.
The climbing lane should be 3.2m wide, the other two being 3.4m each. Appropriate double
white line road markings should be in accordance with Volume 3.
3.3.8.5 Generally, the full width of the climbing lane should be provided at a point "S", 100m uphill
from the point where the sag curve attains a 2% gradient, as shown in Diagram 3.3.8.1. A
taper of 1 in 30 to 1 in 40 should be provided over the 100m length as in Diagram 3.3.8.2
3.3.8.6 The physical width of the climbing lane should generally be maintained to a point "F", 200m
beyond the point where the crest curve reduces to 2% gradient, followed by a 100m taper.
Cross hatching road markings and advance warning signs should be provided in advance of
the taper, to channelise vehicles.(see Diagram 3.3.8.3).
3.3.8.7 At short hills, it may be necessary to commence the climbing lane in advance of point S so
as to provide a minimum length of at least 200m of full width climbing lane. For existing
roads, where crest curves may be substantially sharper than the minimum prescribed, it may
be necessary to adopt a shorter terminal detail so as to prevent the lane reduction extending
too far beyond the crest.