This is draft guidance, and we welcome your feedback

Ongoing inspection and maintenance requirements once a corridor has been cleared.

Any significant changes to the road surface or roadside obstructions should trigger a reassessment of the corridor clearance.

Checking corridor clearance

Inspections recommended to identify any potential corridor clearance issues.

Initial inspection

When a road is being investigated for use as a bus route it is good practice to first complete a trial run of the road to identify any potential corridor clearance issues.

For single-deck bus routes, the public transport authority can ask a bus company to undertake trial runs and provide feedback on any issues encountered such as parked cars or tight turns.

For double-deck bus routes it is good practice to complete trial runs using a single-decker bus with a mock-up to replicate the height of a double-deck bus.

These trial runs should be carried out during quiet times on the road network (weekends or evenings) to reduce the impact on road users from any resulting delays.

During the trial runs the mock-up bus should pull into bus stops and use planned dead-runs and likely diversion routes to replicate, as closely as possible, real operational conditions. In addition, a walk over of the route using a measuring device such as the one shown below should be completed.

Any obstructions identified during the trial runs or walk through should have measurements and photos taken with the location recorded.

This information can then be used to identify any sections of the route that require more detailed surveys and investigations.

Single decker bus with frame on top driving pass a tree

Example of single decker bus with a mock-up. (Source: Auckland Transport, Double decker bus preparation)

Contract worker holding a pole with various horizontal posts to check clearance for a double-decker bus at bus stops.

Example of measuring device for double-deck clearance at bus stops. (Source: Arborlab Consultancy Services)

Ongoing inspections

It is recommended that an annual inspection of bus corridors be completed to identify any existing or future obstructions that need to be managed as part of the annual maintenance programme.

The annual inspections should include both static obstructions (utilities) and changeable obstructions (street trees).

For static obstructions the purpose of the inspection is to identify any assets that may have been installed incorrectly which the road controlling authority is unaware of.

The inspection of street trees should be carried out by a suitably qualified and experience arborist who is able to judge the trees for potential future growth.

The purpose of the street tree inspection is to identify any of the following;

  • larger branches that are dropping into the clearance zone
  • spring shoots that are likely to grow towards the road into the clearance zone
  • any additional trees that are encroaching into the clearance zone.

Maintaining corridor clearance

Maintenance advice to ensure adequate corridor clearance is retained over time.

Road surface maintenance

Road height

Road controlling authorities should ensure that when maintenance works contractors remove the top layer of the road surface prior to reseal, the depth removed is equal to the pavement thickness added. Where there is a net increase in road height the section of road corridor affected should be re-assessed to ensure it continues to meet the clearance requirements.

Road crossfall

During road resurfacing road controlling authorities should also ensure that the crossfall of the road does not increase over time. This is because an increase in road crossfall will increase the amount to which buses tilt thereby decreasing horizontal clearance to potential obstructions.

See 'Crossfall, road camber and superelevation' under Corridor constraints section

Road markings

Where road markings are used as a mitigation measure it is important that the road markings are reinstated correctly after resurfacing and are repainted if the road markings are worn or faded. This should be included as part of the road controlling authority’s road maintenance schedule.

Potholes and wheel ruts

In between road resurfacings, potholes and wheel ruts can form in the road surface along a bus route. This is more common at bus stops which serve a high volume of buses and require drivers to make turning manoeuvres to enter and exit the bus stops. Potholes and wheel ruts create an uneven road surface which can reduce the horizontal clearance as the effective road crossfall is increased.

Furthermore, the uneven road surface can cause double-deck buses to sway as they travel along the route, which increases the movement envelope (also known as kinematic envelope) of the bus, resulting in the bus moving closer to roadside hazards. Bus sway also negatively impacts on the customer experience.

To prevent rutting it is recommended that appropriate road pavement be installed at parts of the bus network that experience high road surface wear such as bus stops and intersections along routes with high frequency services and/or heavy passenger loadings.

The Waka Kotahi NZ Transport Agency Technical Advice note 17 provides guidance on asphalt depths at high stress locations. 

Technical advice note 17: Asphalt depths at high stress locations for new pavements and renewals

Auckland Transport’s Urban street and road design guide suggests concrete ‘bus pads’ to avoid ruts which “cause multiple issues, including increasing bus wear and tear, poor ride quality for passengers, and dangers to cyclists”.

Auckland Transport’s Urban street and road design guide (2019, p.100)(external link)

Tree pruning

Scheduled maintenance

Street trees grow and therefore require regular maintenance to ensure that tree branches do not encroach into the clearance zone. It is recommended that road controlling authorities implement a bi-annual maintenance programme along public transport corridors because trees have two main periods of growth (spring and autumn). Road controlling authorities always have responsibility to maintain clearance. Failure or delay in rectifying clearance issues can pose an imminent threat to road users, particularly for double deck buses.

Trees should be pruned by a suitably qualified arborist to remove the obstruction while protecting the health of the tree. Pruning should be carried out in a way that encourages the tree to grow upwards and away from the clearance zone thereby reducing future maintenance costs.

Reactive maintenance

A visual inspection of public transport corridors should be undertaken to identify trees that may have sustained damage following a storm event, prolonged dry or wet periods, or damage from pests. It may be necessary to delay the use of buses along impacted sections of the corridor until the findings of the visual inspection have been actioned.

Tree maintenance contracts by road controlling authorities should include the provision for public transport operators to report tree hazards and for these issues to be assessed, reviewed and responded to promptly.

New street trees

When developing landscape designs and street planting plans (eg with a landscape architect) it is important to consider the growth profile and the final scale of the mature trees relative to road clearance. This may involve locating the tree further from the kerb or selecting a tree species that tends to grow upwards. Corridor clearance should be considered when road controlling authorities are reviewing proposed street planting plans.

For further details on clearance required, refers to:

Street trees’ in the Specific street elements’section.


Asset maintenance

Over time power and phone lines may require re-tensioning or replacing to ensure that they continue to meet appropriate height clearance requirements. It is important that utility providers regularly maintain power and phone lines, particularly along roads where double-deck buses operate. It is best practice to have ongoing communication between road controlling authorities and utility providers to coordinate the bus operations with utility maintenance.

New assets

When utility providers install new assets, it is expected that the horizontal and vertical clearance recommendations contained in these guidelines are met.

For further details on clearance required, refer to:

Utilities’ in the Specific street elements section.

Temporary clearance measures

In some situations, for example where there are multiple projects planned for the same road corridor, it may not always be possible to coordinate these with bus corridor clearance work.

This could include road maintenance, underground service renewals and cycleway construction.

To avoid the expense of reconstructing recently completed construction work it may be appropriate to use temporary safety measures at the kerb line to keep buses away from roadside hazards.

For horizontal clearance, this could include:

  • using flexi-posts at the kerb line to discourage drivers from manoeuvring close to or over the kerb
  • temporary kerb buildouts such as those illustrated below.
kerb buildouts guide double-deck buses away from hazards along the kerb

Temporary “kerb buildouts” to guide double-deck buses away from hazards along the kerb (Source: Thomas Chu)

However, these safety measures should only be used as a temporary solution until a more permanent upgrade can be implemented.

Temporary measures require frequent monitoring, maintenance and replacement if appropriate. It is not appropriate to use warning signs either temporarily or permanently if clearance has not been achieved because this does not allow for driver error.

The potential consequences can be severe as illustrated in this example from the UK. 

bus collision in the united kingdom showing poor signage

Incident from the UK where signs were not sufficient to prevent a bus collision. (Source: WENN)