15.2 Key Considerations
Signing and marking through interchanges is essential to their efficient operation. A major criteria for acceptability of a layout for an interchange is the ability to properly and effectively sign that layout to make it work. Significant issues to be considered include the following:
- location of signs to ensure adequate decision times
- positioning of the signs with respect to the major road lanes (either overhead on gantries or mounted to the side)
- location and type of support legs for the signs – non-frangible sign supports must not be placed in the gore areas at ramps or in run-out areas
- gantry signs are essential for major forks to avoid driver confusion because the gore is long and narrow to accommodate the large radius curves involved
- gantry signs are far more effective for carriageways with three or more lanes (refer to AS 1742.15)
- frangible sign supports and lighting poles must be used if the sign supports and lighting poles are not protected by safety barrier
- non-frangible sign posts and lighting poles must be located behind safety barriers or protected with appropriate devices.
- signs should be clearly visible in all conditions and the sign face material should be chosen to provide the required properties (e.g. Class 1 retro-reflective material). Individual lighting of signs should be considered if the ambient or general lighting is not adequate.