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Engine brakes are a type of supplementary braking system provided on heavy vehicles to assist the normal ‘service brakes’ in maintaining safe speeds travelling down hills. The regulation of engine braking and the management of its potential disturbance of nearby communities is described.

  • What is engine braking?

    Supplementary braking systems are provided on heavy vehicles to assist the normal ‘service brakes’ in maintaining safe speeds travelling down hills. There are three main types of supplementary braking systems:

    • Exhaust brakes: a device intermittently blocking the exhaust to create back pressure on the engine.
    • Engine brakes: a device releasing compressed gases from the engine.
    • Retarders: electric or hydrodynamic devices installed in the driveline.

    Engine brakes are typically used on large trucks, whereas exhaust brakes are common on medium trucks. 

    Modern engine and exhaust brakes include silencers and are unlikely to cause significant noise disturbance.  

    Some older heavy vehicles have unsilenced or ineffectively silenced engine brakes which produce loud noise and may cause noise disturbance.

    Further details can be found in this leaflet [PDF, 331 KB]

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  • What does engine braking sound like?

    Engine and exhaust brakes give rise to a series of noise pulses, which can have a distinctive sound, often described as a ‘machine gun’ or ‘barking’ noise. 

    Other vehicle noise such as normal heavy vehicle acceleration/deceleration can produce noise commonly confused with engine braking, as can the sound of vehicles travelling on rumble strips.  Monitoring has shown the occurrence of ineffectively silenced engine braking is quite low, even in areas of significant reported disturbance.  

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  • How often does engine braking occur?

    The Transport Agency has completed long-term monitoring of engine braking at several locations across the state highway network. This monitoring indicates the frequency of engine braking is generally quite low - often less than one event per day - even in areas where residents report frequent disturbance from engine braking.  

    This monitoring has shown loud noise from engine braking is not as frequent as loud noise from other vehicles, such as motorcycles, modified cars and sirens or other heavy vehicle noise - such as acceleration/deceleration noise without engine brakes.  

    Other vehicle noise such as routine heavy vehicle acceleration/deceleration can produce noise which is commonly confused with engine braking, as can the sound of vehicles travelling on rumble strips.

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  • What can the Transport Agency do about noise from engine braking?

    The Transport Agency has limited ability to influence the use of engine brakes on the road. The primary tools are liaison with trucking operators and industry groups to influence driver behaviour and also liaison with the NZ Police to identify areas for potential enforcement of excessive noise rules. The Transport Agency does not have an enforcement role for on-road use of engine brakes.

    The Transport Agency can undertake engine braking monitoring to identify the scale of the potential engine braking problem in the area and identify individual vehicles that are using engine brakes.  This information is not used for enforcement but rather to assist and focus liaison with the trucking industry and the NZ Police. 

    In some circumstances the Transport Agency can provide signs either advising no engine braking or prohibiting engine braking. An engine braking prohibition requires consultation and enactment of a bylaw and can only be implemented if the posted speed limit on the road is 70 km/h or less.  More information can be found about engine braking prohibitions in the Land Transport (Road Safety and Other Matters) Amendment Act 2011(external link).

    Additional information on how the Transport Agency manages noise disturbances from trucks engine braking on state highways can be found in this technical memorandum [PDF, 75 KB].

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  • Will you monitor for engine braking at the road near my house?

    The Transport Agency has two special noise monitoring devices with cameras to record engine braking events and the details of the vehicles engine braking. The decision to install a noise camera is based on the following: 

    • likelihood engine braking would occur in an area
    • number of houses nearby the road which might be disturbed by engine braking
    • availability of a suitable location to install the noise camera
    • community documentation of engine braking (date, time and location of observed engine braking)
    • extent of the actual adverse effect occurring, as demonstrated by the number of residents reporting disturbance from engine braking noise
    • availability of funding to install and manage the monitoring equipment.

    There is typically a waiting time of one to two years from the time a location is identified to install the noise camera and the actual installation. This is because the two cameras are prioritised across the entire state highway network and there is generally a waiting list. 

    The information generated from the noise camera is used for liaison with the trucking industry and individual drivers to advise of the disturbance caused by engine braking, and to influence behaviour to reduce engine braking in built up areas where it is most likely to cause disturbance. 

    This information may also be shared with the NZ Police to help them focus enforcement of excessive noise rules. However, the monitoring cameras themselves are not used directly for enforcement.

    Further details can be found in this leaflet [PDF, 331 KB].

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  • What can I do to help identify vehicles that use their engine brakes?

    If you are experiencing regular or routine disturbance by engine braking noise, documentation of this information can assist the Transport Agency to liaise with organisations that might be able to influence driver behaviour.  

    Keep a log of date and times when you observe engine braking over a period of two weeks (ideally longer). In most instances it is not practical to identify individual heavy vehicles potentially engine braking but if you can document information identifying the vehicle (such as company name) this can be helpful with liaison efforts. 

    This information may be used by the Transport Agency for liaison with the trucking industry to advise of the disturbance caused by engine braking, and to influence behaviour to reduce engine braking in built up areas where it is most likely to cause disturbance. This information may also be shared with the NZ Police to highlight community concerns and help them focus enforcement of excessive noise rules, if appropriate.

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  • Will you provide a 'no engine braking' sign on the road near my house?

    In some circumstances, the Transport Agency can provide signs either advising no engine braking or prohibiting engine braking. 

    Several factors are considered prior to installing ‘no engine braking’ signs. These include the following: 

    • safety implications of limiting engine braking on the road
    • likely effectiveness of signs in reducing engine braking
    • likelihood that engine braking would occur in an area
    • number of houses nearby the road which might be disturbed by engine braking
    • community documentation of engine braking (date, time and location of observed engine braking)
    • number of people reporting disturbance from engine braking in the affected area.

    An engine braking prohibition requires consultation and enactment of a bylaw and can only be implemented if the posted speed limit on the road is 70 km/h or less. This is because engine brakes are important supplementary safety device for slowing vehicles down in some situations, for example on higher speed roads or on steep declines.  

    More information can be found about engine braking prohibitions in the Land Transport (Road Safety and Other Matters) Amendment Act 2011(external link).

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  • Do ‘no engine braking’ signs really work?

    No specific studies have been completed to assess the effectiveness of ‘no engine braking’ signs. It is considered such signs are likely to have limited effectiveness but would most likely be beneficial in areas where drivers might not realise there are nearby dwellings which may be disturbed by engine braking. The Transport Agency still receives reported disturbance from engine braking noise in areas where signs have been erected.  

    Overuse of signs, including ‘no engine braking’ signs, can cause visual clutter or habituation, meaning the messages that signs convey may not be readily noticed or actioned by drivers. As a result, installation of signs should be carefully assessed to make sure they are likely to be effective in reducing noise disturbance caused by engine braking.

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  • Who enforces no engine braking signs?

    NZ Police are responsible for enforcing the Land Transport (Road User) Rule for excessive noise for on road vehicles. This includes engine braking noise deemed to be excessive. The enforcement of the excessive noise rule for engine braking may occur regardless of whether there are ‘no engine braking’ advisory or prohibitory signs.

    The Land Transport (Road User) Rule includes the following provision (rule 7.4) for on road vehicle noise:

    “A driver must not operate a vehicle that creates noise that, having regard to all the circumstances, is excessive.

    In determining whether any noise is excessive, regard may be had, in addition to all other relevant matters, to—

    (a)  the manner of operation of the vehicle:

    (b)  the condition of the vehicle:

    (c)  the time of the day when the noise is created:

    (d)  the locality where the noise is created:

    (e)  the likelihood of annoyance to any person:

    (f)  any relevant standard or specification that applies under the Act.” 

    Where there is a bylaw prohibiting engine braking a fine can be specified. The specific provisions contained in any bylaw will determine who might enforce it. If the bylaw is simply a ban on the use of engine brakes by heavy motor vehicles it would normally only be enforceable by NZ Police.

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  • How is noise from individual heavy vehicles regulated?

    Section 2.7 of the Land Transport Vehicle Equipment Rule sets out noise requirements for vehicles entering service (i.e. vehicles being imported and/or registered in New Zealand for the first time).  In summary, this rule requires most vehicles entering service be manufactured to a standard complying with the noise levels. If the vehicle has been modified to increase the noise output from the original (complying) exhaust system, then individual testing of the vehicle may be required before it can enter service to demonstrate that the maximum noise levels are not exceeded.

    For in service vehicles (ie  vehicles already registered in New Zealand) the Land Transport (Vehicle Equipment) Rule requirement is they not ‘be noticeably and significantly louder than the noise output from the vehicle’s original exhaust system at the time of the vehicle’s manufacture.’ This may be confirmed during the certificate of fitness (CoF) inspection process for heavy vehicles. There are no in service maximum noise levels for heavy vehicles.

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