Upgrading Rural Bridges for Improved Freight Efficiency
Wayne Davies, Transport and Main Roads
This paper presents three proposed approaches to the cost benefit analysis of upgrades to bridges that are subject to load or height restrictions. The paper further elaborates with the inclusion of two actual case studies from Queensland Australia.
This paper focuses on the methods and approaches of evaluating the benefits of upgrading bridges that are currently structurally deficient to carry vehicles above certain tonnage or do not cater for certain heavy vehicle dimensions. Many of these bridges are located in rural areas where traffic volumes tend to be low. Benefits for most road projects are driven by traffic volume. If a project has high capital costs and low traffic volumes, a cost benefit analysis (CBA) would normally imply the project is not economically viable.
The extent traffic volume is a causation of benefits for bridge upgrades is not as obvious as for other road project types. In this paper, the key determinants for deriving benefits for these bridge upgrades are discussed in some detail. These key determinants include the number of heavy vehicles, extent of restrictions (tonnage, size and length), length of diversion route required by heavy vehicles to avoid load and size restricted bridge/s, total distance heavy vehicles are required to travel to reach their destination and the maintenance costs required if the bridge is not upgraded.
In this paper, three approaches of evaluating benefits of upgrades to bridges are discussed. These approaches centre on the behaviour of heavy vehicle road users when a bridge can no longer be traversed due to structural deficiencies. First approach assumes heavy vehicle road users will divert to avoid the bridge, second approach assumes heavy road users will switch to smaller vehicles that are within the load restrictions of the bridge and the third approach is a hybrid of the first two approaches. To demonstrate the above-mentioned approaches, two case studies from Queensland Australia have been included in the paper.
Association for European Transport