Heavy vehicles will face a 20.4 kilometre detour for most of 2014 once work on the Picton Road-M1 Princes Motorway intersection begins next month.
The Roads and Maritime Services (RMS) work is designed to improve safety for vehicles turning left from Picton Road onto the M1 by replacing the T-intersection with a new 700-metre northbound acceleration lane.
At present, heavy vehicles must stop before turning left and then turn onto a road with traffic travelling at 100km/h.
The $5.5-million project will create a lane that will allow heavy vehicles to get up to speed before merging onto the M1 Princes Motorway.
Other work will include a two to three-metre wide shoulder on the M1 Princes Motorway, as well as a retaining wall at the southern end of the acceleration lane.
Work will start on January 28 and the left-turn lane onto Mt Ousley Road will be closed for the duration of the project - which is expected to take eight months.
During this time heavy vehicles will be forced to take a 20.4 kilometre detour north along the Hume Motorway and then travel to Campbelltown and along the Appin Road.
The RMS estimate the detour will add an extra 25 minutes to each trip.
Light vehicles will turn right off Picton Road onto Mt Keira Road and then Clive Bissel Drive before rejoining the M1 at the top of Mt Ousley.
The light vehicle detour will add an extra 3.5 kilometres and approximately three minutes to a trip.
Also, to prepare the area for the road work, full closures of the M1 between the Picton Road interchange and Bulli Tops will be required.
To minimise the disruption to motorists, these closures will take place between 8pm and 5am.
The southbound lanes will be closed at night from January 19-23, while the northbound closures will take place from January 28-30 and February 2-4.
During the closures light vehicles will use Bulli Pass while heavy vehicles can use Picton Road.