2.2.1 Design Information
The Guide to Road Design Part 2: Design Considerations (Austroads 2015b) provides information that needs to be considered in the design of a road that is also relevant to interchanges and Table 3.1 of that Guide summarises the factors for consideration, and the type, nature and likely sources of the information required.
Key aspects that require consideration for interchange design include:
- safety performance of possible treatments
- topographic details
- land use details
- environmental conditions and constraints
- cultural heritage values
- property details and values
- structural clearances
- location and nature of utility plant and equipment
- geotechnical data
- access requirements in the area
- drainage and flooding issues
- landscape requirements
- accommodation of public transport facilities
- pedestrian and cyclist facilities
- location, standard and function of the intersecting roadways that the interchange will be serving.
The style, economy and layout of an interchange will be heavily dependent on the topography and other physical constraints existing at the site. Rolling and hilly topography presents opportunities to mould the design of the interchange into the landscape and take advantage of level differences to reduce cost. In flat terrain, the design will have to create the level differences occurring naturally in undulating country and detailed attention to the relative grades will be required to achieve the most economical and visually pleasing result.
Interchanges require a significant area of land and the availability of right of way can influence the type of interchange adopted. The detailed location of the facility may also have to be tailored to the available land with appropriate adjustments to the local road system to ensure that the facility is properly used.