FactSheet - Bridges on Private Property
Bridges and culverts on private property are a risk if they are not inspected or maintained, or are used for purposes for which they are not suited. There have been multiple accidents causing death or serious harm.
How?
Many bridges on private property have no specified live load carrying capacity or overweight ratings, and have few (or no) records of design and construction. Because of the cost involved, they are usually never inspected by bridge inspectors, and landowners and users tend to have a “she’ll be right” attitude.
Owners and users of bridges on private property place themselves and others at risk if there is insufficient evaluation of the strength and deficiencies of a bridge, the type of vehicles, loads and axle weight restrictions of vehicles using the bridge, as well as the speed of vehicles on the bridge.
Significant Issues
Design
- Bridges built on private property are generally old and built to accommodate smaller vehicles and equipment.
- Some older bridges do not have inspection certification, plans or design information.
- Treatment of timbers used in older bridges varies. Even treated timber bridges of a certain age can be inadequate in many cases.
- The decks on some bridges can have a reasonably large cantilever which extends out unsupported, with the kerb on the outside edge of the deck. Generally a cantilever should be no more than 500mm to the inside edge of the kerb.
Use
- Modern vehicles and equipment are larger and heavier.
- The wheel base of loaders, machinery and other equipment may be wider than the bridge’s beams.
Maintenance and inspection
- The weight-bearing capacity of a bridge cannot be determined by visual inspection without some expert and background knowledge.
- Farmers/landowners/users generally don’t know how to determine if a bridge is appropriate for the purpose of use if an inspection and certification has not been carried out.
- A building permit is required to build a bridge, but it is not required for the maintenance of the bridge.
- There are costs associated with inspection of a bridge by a bridge inspector or bridge engineer, and there are three separate levels of inspection and certification. Costs vary accordingly.
There is no formal compliance regime, so it is recommended that land owners, users, and contractors run through a visual inspection checklist to ascertain if the bridge is fit for purpose. Should there be any doubt, an expert should be consulted.
- Check deck condition. Are there any rotten boards? Is there good drainage or is it slippery?
- Check that the distance of the cantilever from the supports under bridge is not excessive (e.g. approximately 500mm).
- Check that coatings on steel structures are in good condition. Is there any obvious corrosion of bolts or fittings?
- Check for deterioration of concrete, e.g. corrosion of exposed reinforcing in beam piles or abutments; cracks in beams, piles or abutments.
- Check for decay in timber piles, and for rusting/corroded fixings.
- Consider the impact of built-up debris in the river, which may weaken the support structures. Also, consider the effects of erosion on banks and river beds, as this can affect the stability of structures. (Note: if there is any concern, an accurate determination by a bridge inspector and certification should be arranged.)
- Check for damage, e.g. impact damage from vehicles, especially to guardrails and handrails.
- Check that the approach to the bridge is suitable for types of vehicles accessing the bridge. This includes angle and road conditions.
- Consider whether the structure of the bridge is suitable for types of vehicles accessing the bridge –
- Is the vehicle a single or tandem unit with one or more sets of wheels on the bridge at the same time?
- Check with any contractors using the bridge about the weight of the vehicle and load weights.
- Consider whether wheel widths and speeds of vehicles are appropriate for the bridge. (Note: accurate determination of this needs a Bridge Inspection and certification.)
- Consider signage at the approach to the bridge if restrictions are necessary. The strength of the bridge on private land should be notified either by a notice held by the owner, or a sign on the bridge itself, so that anyone using it with a heavy vehicle knows what weight or load it can safely carry. (Note: accurate determination of this needs a bridge inspection and certification.) The Transit New Zealand Manual proposes solutions for mitigating risks posed by weak bridges until action can be taken to strengthen or replace them, such as:
- imposing a speed restriction;
- imposing vehicle gross weight and/or axle weight restrictions;
- limiting the number of heavy motor vehicles permitted on the bridge at the same time
- closing the bridge to heavy motor vehicles and rerouting the heavy motor vehicles around a bypass e.g. via an adjacent bridge or through a stream.
Further evaluation
- Check for any stamps or markings of the bridge builder on or around the bridge – this may also include the dates the bridge may have been built. Information may be available from the builder. Check if the bridge has been rated for maximum load.
- Check the availability of any plans, design specifications or information on file from District or Regional Councils, or from the bridge builder if known.
- Check your City, Regional or District Council to find out their rules about who regulates the bridging of rivers and streams within the region under the Resource Management Act 1991.
- Regular inspections by a suitably qualified person of all bridges with a length exceeding three metres and height of two metres can significantly minimise the risk.
Further Information
Further information on bridges, bridge inspection and maintenance, and weight rating and limitations may be found at the New Zealand Transport Agency website.
