Road traffic vibration

The causes of vibration from road traffic are complex and can depend on numerous factors such as road surface imperfections, the speeds of vehicles, the weight of vehicles, weak soils, and building foundation/construction type, or building condition.

There are several factors which influence the road traffic vibration felt within a property.

• Distance of building from the road:
  Road traffic vibration levels generally decrease with distance from the road. A person in a building further away from the road is likely to experience lower levels of road traffic vibration compared with a person in a building sited close to a road.
• Road surface condition:
  In some instances, an uneven road surface with a defect such as a pothole, rutting (grooves caused by wheels), or uneven spots in the road where utility covers (such as manhole covers) stick up or sink down can be the cause of a vibration sensation. When road surfaces deteriorate over time, this can cause defects that can contribute to road traffic vibration.
• Traffic conditions:
  Road traffic vibration is related to the number of vehicles travelling a road per day (which affects the frequency of vibration), the speed of traffic (higher speeds means high vibration levels), and the number of heavy vehicles using a road such as trucks and buses. Our investigations found higher speeds of heavier vehicles resulted in higher monitored road traffic vibration levels; however, the vibration levels were still below the threshold for property damage.
• Ground or soil conditions:
  The extent of vibration, and the distance vibration levels are felt, can depend on both the soil type and the layers of soil. Vibration travels further in hard/stiff soils than in loose/soft soils. Vibration can also move more easily and faster in hard/stiff layers of soil than through softer ones.
• Building foundation/construction type and condition:
  Vibrations are more likely to be felt in buildings with foundations in poor condition, foundations with ‘rigid’ connections between the ground and the building, and/or buildings where the contact between the ground and the foundation makes up a large surface area. Timber or concrete floors can also contribute to the vibration levels felt inside a building.

In most cases normal daily household activities (such as walking in a house, cleaning, cooking, etc.) cause vibration levels greater than that from road traffic. These types of activities are less common at night and thus background vibration levels are generally lower. As a result, when vibration occurs at night, it may seem to be worse, but it is likely just more noticeable in the absence of other sources of vibration. Also, at night when we are trying to sleep, lower levels of vibration may cause more potential disturbance than they would during the day.

In some circumstances trucks may be travelling at higher speeds at night (e.g. in rural towns) which may lead to an actual increase in vibration.

Concerns about vibration can be heightened by noise, for instance the noise of a loud truck passing by may cause your windows to rattle, or ground vibration might cause glasses in a cabinet to rattle. Noticing noise may make vibration levels seem greater than they are. This is particularly true at night when it is generally quieter inside and outside a house, and both noise and vibration are more noticeable.

We’ve investigated concerns about road traffic vibration with acoustic (noise and vibration) consultants and their advice is that while road traffic vibration might cause concern or disturbance, the vibration levels seldom reach levels which would cause damage to buildings or structures. The work undertaken reflects similar findings across Council’s transport network which has informed our approach to vibrations.

An acoustic consultant (an expert specifically focused on vibrations) was engaged in Auckland to monitor road traffic vibration in residents’ homes. The purpose of the monitoring was to determine whether the road traffic vibration had reached a level that adversely impacted a residential dwelling. Due to the broad range of factors contributing to vibration, monitoring was focused on:

• measurement of road traffic vibration levels within residential homes that were on a bus route with speed tables
• using different sized test buses with drivers travelling through the bus route at varying speeds
• measuring the existing speeds of vehicles on the approach to and departure from the speed table · counting the number of heavy vehicles using the street during the monitoring of road traffic vibration levels
• a qualitative survey of three bus passengers at the front, centre and rear seats of the test buses.

Findings from the monitoring:

• The monitored road traffic vibration levels have been found to be at an acceptable level and did not reach a threshold level that is known to cause damage to a residential building.
• The perception of road traffic vibration varies between people and while few people can feel low vibration levels, most people do not feel road traffic vibration or find it a nuisance. This is observed on roads other than the test road where a single resident raises road traffic vibration concerns and other residents have not.
• An uneven road surface or road surface imperfection on the road is a contributing factor to road traffic vibration. This can be exacerbated when heavy vehicles travel over these imperfections at higher-than-average speeds.
• Higher speeds of heavier vehicles resulted in higher monitored road traffic vibration levels; however, the vibration levels were still below the threshold for property damage.
• The passenger at the rear of the bus consistently experienced the worst comfort out of the three passengers when the bus driver travelled at higher than usual travel speed.

Our process for road traffic vibration complaints usually begins with desk-based research to consider possible contributing factors. In some cases, it may require Council to undertake a site visit. If a site visit is undertaken, we will check: 

• Whether the uneven road surface is a potential contributing factor to road traffic vibration. If so, remedial works will be planned, noting that most of the network’s road surface is maintained to a level that is safe and efficient for road users.
• Existing infrastructure. Where there are existing speed reduction measures in place, the construction is checked against specifications to ensure they meet the correct standards. If there are any significant issues identified, we will work toward possible solutions, including potential additional signage or road marking.
• Driver speeds. For most roads in Tauranga, drivers are travelling at safe and appropriate speeds. However, if there are existing speed reduction measures which are not having the appropriate impact on driver speeds, we consider whether signage or road markings could support lower driver speeds on a given road.

Council does not routinely undertake vibration monitoring at properties in response to customer complaints and queries.

Undertaking this type of monitoring for every customer with concerns about road traffic vibration is a costly exercise within a limited budget. Additionally, there are several other contributing factors to the road traffic vibration which are beyond the control of Council. See ‘What factors contribute to road traffic vibration’ above.

People can feel vibration at levels approximately 10 times lower than the level where minor building damage may occur. It is highly unlikely road traffic vibration would cause cracks or other structural or aesthetic damage to buildings. Typically cracks and other similar damage result from building construction defects, natural building ageing effects or ground movement (beneath foundations), such as that resulting from clay shrinkage or building settlement.

However, people can notice existing damage such as cracks in a wall or ceiling lining if they notice vibration from a road or other sources. This is because feeling vibration can raise concern of damage and can draw attention to existing damage that was previously unnoticed or forgotten.

When someone claims that private property damage has been caused by road traffic vibration, there is a requirement by Council that evidence is provided to substantiate these claims to ensure that results are independently verified by suitably qualified experts.

If you think your property has been damaged by road traffic vibration, we suggest you lodge an insurance claim or provide evidence to Council. Typically, this would be a claim with your property’s insurance provider to obtain an independent assessment of any damage. This can then be presented to Council by your insurer. Alternatively, this evidence may be in the form of an assessment from an independent consultant who has assessed your property.