A variable message sign will be installed on Windsor Road, 40 metres south of Chelsea Avenue at Baulkham Hills.
Roads and Maritime Services will monitor the effectiveness of the sign as part of the statewide network of permanent variable message signs.
Baulkham Hills state MP David Elliott said the RMS would plant trees on the north-western side of Windsor Road, to reduce the visual impact of the sign.
Work is expected to start in the last quarter of 2013.