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This is draft guidance, and we welcome your feedback |
Elements of our streets (eg utility poles, trees etc) which can pose a clearance risk to public transport and detailed clearance advice for each of these elements.
Note for the essential overall vertical, horizontal and underside clearance dimensions for public transport corridors see the General clearance requirements section:
General clearance requirements
Street trees and vegetation are part of the built environment.
Street trees can pose a significant challenge in achieving corridor clearance, particularly when the corridor is used by double-deck buses. This is because trees are often located close to the kerb and tend to grow out over the urban street or road corridor. For example, tree branches pruned to the recommended minimum of 4.8m may re-grow, including downward growth over time reducing the clearance.
Arborists should consider thickness and angles of tree branches when cutting to ensure that wind and re-growth does not impact the effective clearance beyond 4.6m. To achieve this, arborists may suggest some additional clearance/cutting in some instances.
Street trees have high amenity, environmental and sometimes cultural and heritage values, therefore the heavy pruning or removal of trees can attract stakeholder and public interest. Furthermore, some trees are protected including those by waterways, along the coast and in district plans meaning resource consent for pruning or removal may be required.
Scoping the location of trees and vegetation early in the planning phase can assist to avoid issues and develop options to address clearance issues. The condition, age and species of the tree can limit options to alter street trees.
Councils should seek the advice of a suitably qualified and experienced arborist to assess and establish how best to achieve corridor clearance when the corridor includes street trees.
Corridor clearance can also be achieved by moving the bus further into the middle of the road by changing road markings or building out kerbs.
The feasibility of road narrowing depends on the road space allocation, for example the width of traffic lanes or parking being wider than is needed.
Examples of a bus stop with street trees near the kerb. (Source: Andy Maule)
For tree maintenance advice refer to the following:
Maintaining corridor clearance section on tree pruning
Shop verandahs are a common feature along retail streets in New Zealand.
Some towns and cities require shop verandahs as part of their bylaws and District Plans to provide weather protection to pedestrians and contribute to the local character.
Verandahs are commonly built at a height of 3m above the footpath and can extend close to or past the kerb. See photo below.
Example of bus stop with a shop verandah that has resulted in temporary treatments advising drivers not to pull into the kerb, reducing the accessibility and operability of the bus stop (Image by Lorelei Schmitt)
Under the Local Government Act, road controlling authorities legally own the road and airspace above the road corridor. Therefore, Councils have the authority to require shop owners to alter verandahs that extend over a road to enable the safe movement of people and vehicles.
Verandahs that are within 1.0m of bus stops should ideally be altered or removed. In practice modifications to the verandah can be complicated and expensive. This is because any modification work is likely to require written approval from the property owner, building consent and potentially resource consent.
Other alternatives to achieve the necessary corridor clearance include relocating the bus stop to a less constrained location or building out the kerb.
Potential obstructions from utilities include low hanging power or phone lines and utility poles for power and lighting.
The New Zealand Electrical Code of Practice for electrical safe distances (NZECP 34:2001) requires utility service providers to maintain power lines at a minimum height of 5.5m above the road surface.
In practice some power and phone lines may not always be maintained at this height and should be raised to achieve the minimum height clearance. Similarly, utility poles can be found within the minimum horizontal clearance requirement of 1.0m from bus stops or 0.5m at other locations along the bus route.
The National Code of Practice for Utility Operators’ Access to Transport Corridors (linked below) requires that new installations be positioned at maximum practicable separation from the Carriageway and as close as practicable to the property boundary.
It is important to account for the fact that power and utility cables may stretch in the heat, sunshine, or over time, thus reducing clearance.
Low hanging power and phone lines can be raised to the required height, which is often the best option for removing this obstruction.
For utility poles located within the required horizontal clearance options include relocating the poles or undergrounding the power lines. However, both these options are expensive and therefore Councils should also consider relocating bus stops to between utility poles and the use of kerb build outs.
Councils should consult with utility providers early in the corridor clearance process to agree a works programme and cost sharing arrangement.
If utility poles are relocated, then Councils must ensure a suitable footpath width (recommended to be at least 1.8m wide but certainly no less than 1.5m wide) can still be achieved to maintain access for all street users including those with wheelchairs or prams.
For further details on accessible footpath widths refer to the following guide:
Pedestrian Network Guide on accessible footpaths
For further information on installing utilities refer to:
Street furniture including sign posts, seating, rubbish bins, parking machines and bus stop shelters can conflict with bus front and tail swing.
Street furniture within 1.0m of the kerb face can often be relocated and therefore presents less of a challenge than other types of obstructions.
When relocating street furniture Councils must ensure a suitable footpath width (recommended to be at least 1.8m wide but certainly no less than 1.5m wide) to maintain access for all street users including those with wheelchairs or prams.
Note some councils may have a greater minimum specific to their jurisdictions, where the local guideline exceeds the recommended minimums in this guideline, the local guidelines should take precedence. For example, Auckland Transport advises 2m footpath widths.
Fixed structures such as low bridges and tunnels can constrain the use of double-deck buses due to the high cost associated with increasing clearance.
Measures to increase clearance could include lowering the road under a bridge and excavating the roof or sides of a tunnel.
In practice it may be difficult to justify such measures and therefore alternative routes or fleet options may need to be investigated.
Road surfacing is a factor that can present obstructions to public transport operations in its own right or can reduce clearance to other types of obstructions.
The elements of road surfacing that should be considered for public transport corridor clearance include:
In general, the smoother and more uniform the road surface, the easier it is to operate public transport vehicles and the better the customer experience is.
Where crests, dips and tilts in the road surface cannot be avoided then it is preferable to have a gradual transition between road features.This is particularly important for high speed roads and where there are sharp corners as these factors contribute to greater bus sway.
There are aspects of geometric design of road surfaces that can affect corridor clearance.
Crossfall is the generic term for a difference in level between parts of the road surface measured perpendicular to the direction of travel.
The primary reason for crossfall on a road surface is to drain surface water as quickly and effectively as possible.
This is achieved by draining water across the road surface and travel lane to a gutter or channel, often formed by a kerb, or a simple a roadside ditch or verge. From there, longitudinal fall controls the water flow to a collection or discharge point.
Camber is a term used to describe the shape of the road surface and includes changes in crossfall across the road eg crowned or curved.
The below image shows a cross section of a typical urban road with a crown (high point) in the centre of the carriageway with crossfalls to kerbs on either side.
Diagram showing road crossfall for a crowned road (not drawn to scale).
Superelevation is crossfall that is usually applied in a single plane across the road (as illustrated below).
Diagram showing road crossfall for a superelevated road (not drawn to scale).
Roads are typically designed with superelevation on corners or sweeping curves, for the purpose of improving vehicle cornering performance and passenger comfort by managing the outward forces on a vehicle.
Dependant on the radius and the speed environment, superelevation usually varies between 3% and 10% and are not generally applied in urban environments where the operating speeds are less than or equal to 50 km/h.
Road designers should refer to the Waka Kotahi technical memorandum TM-2501: Superelevation calculations with supporting information in the State Highway Geometric Design Manual when designing superelevation:
Waka Kotahi technical memorandum TM-2501: Superelevation calculations
State highway geometric design manual
The higher the crossfall, the more a bus will tilt which brings the top corner of the bus closer to any roadside obstructions on the lower side.
It is preferable to have a crossfall of around 3% which is generally effective at removing surface water. Where site constraints mean that this cannot be achieved designers should consider bus tilt when designing roads with steeper crossfall gradients (including camber and superelevation). Designers should also ensure that there is a smooth transition between different gradients to minimise swaying for double-deck buses.
A double-deck bus tilting out towards the kerb (Photo credit: Tim Wedmaier)
Austroads, Guide to Road Design Part 3, Geometric Design, Section 4.2.2(external link)
