Key Points:

This weekend marks the start of the Christmas holidays for much of the population. It is also the cue for construction work to crank up on roads, railways, bridges and tunnels around Auckland - and for motorists to look out for detour signs.

Transit NZ will close the two southbound clip-on lanes on Sunday night, Christmas Eve, for two weeks until January 7 for re-surfacing. The southbound motorway exit to to Shelly Beach Rd and Ponsonby will therefore also be closed.

Transit urges motorists heading across the bridge from North Shore on Christmas Day to allow an extra 30 minutes. Three lanes of the bridge will be kept open in each direction.

Transit wants motorists to take extra care on Auckland's motorways, where new links have opened in some places and construction work will mean detours in others.

* Southwestern Motorway-Hillsborough Rd: The Auckland end of the Southwestern Motorway will be closed to all but westbound local traffic for a fortnight from next Wednesday, December 27, for work for the extension of State Highway 20 through Mt Roskill.

Hillsborough Rd around its intersection with the motorway will be closed in both direction between Littlejohn St and Herd Rd.

Visitors from the airport and elsewhere should watch for signs recommending detours through Onehunga or Queenstown Rd until a giant roundabout opens on January 7, ready for Transit contractors to build a motorway interchange over the following two years.

* Northern Motorway: Transit will close the southbound onramp to the Northern Motorway from Constellation Drive between December 27 and January 14 while a duct is laid for a Transpower cable.

Constellation Drive will be narrowed to one lane in each direction on its approaches to the motorway, and traffic will be restricted to left turns only into Constellation from the interchange's southbound off-ramp.

* Fanshawe St: A similar duct-laying operation will, from December 27 to late January, prevent traffic heading from the motorway from turning left into Beaumont St from the Fanshawe St off-ramp.

* Spaghetti Junction: Transit urges Aucklanders and visitors to pay special attention to overhead and variable message signs around the Central Motorway Junction as motorists get used to four new links, some of which are controlled by ramp signals.

* Travelling north: Motorists will be invited to use State Highway 16 between Auckland and Wellsford to ease congestion on the Northern Motorway and the Hibiscus Coast Highway.

Government agency Ontrack will take advantage of the Christmas break to accelerate progress on $55 million of new tracks and platforms between New Lynn and Henderson, part of a wider programme to duplicate the western line in a $600 million redevelopment programme for the Auckland rail network.

The agency also plans to use the break to shore up the railway bridge over Ronayne St near the waterfront and to renew tracks and improve drainage in the Parnell tunnel, both of which have been under speed restrictions. Shuttle buses will replace trains for various periods.

* Waitakere to New Lynn: The railway line west of New Lynn will close from Saturday until January 8 for new platforms to be built at the Fruitvale and Glen Eden stations. Each platform will be made long enough for six-car trains..

The Auckland Regional Transport Authority will deck out the platforms with new shelters, lighting, signage and CCTV security cameras. New footbridges are also being built at Glen Eden and at Sunnyvale Station (the first of two new platforms opened this month).

Buses will carry rail passengers along the route except for Christmas Day, when no trains run in Auckland, and on Sundays.

* Newmarket to Britomart: Trains will stop running on the southern line from Newmarket to central Auckland from Wednesday to next Saturday for work on the Ronayne St bridge and Parnell tunnel.

Buses will be used to carry rail passengers on those days between Newmarket and Britomart, and between Waitakere and Britomart.

Buses will run throughout the Christmas and New Year break, although on Sunday or holiday timetables on various days. All Stagecoach and North Star bus services will run free of charge on Christmas Day.

Devonport and Waiheke Island ferries will sail each day, but others including those for Bayswater, Birkenhead and Gulf Harbour will stop for Christmas and New Year statutory holidays.