This route is . Road conditions SH 1 has varied road conditions. For most of its length it is a two-lane single carriageway road with at-grade intersections and access, sealed with chipseal in rural areas or asphalt in urban and high-traffic areas. The highway has frequent passing lanes on these sections, to allow traffic to pass other vehicles safely. Parts of the road are steep by international standards. Most steep sections having a combination of passing lanes (uphill), and crawler lanes or stopping bays (downhill) to allow heavy and slow vehicles to pull out of the way to let other vehicles pass. The New Zealand Transport Agency (NZTA) classifies the most part of State Highway 1 as a national strategic road. The exceptions are between Kawakawa and Whangārei and south of Mosgiel, where the SH 1 is classified as a regional strategic road, and north of Kawakawa where SH 1 is classified as a primary collector road. The sections between Wellsford and Wairakei, between Ohau and Wellington Airport, and between Woodend and Rolleston are classified as high volume roads. The section from the Central Motorway Junction and the Newmarket Viaduct, to the south, is the country's busiest section of road, with more than 200,000 vehicle movements a day between Khyber Pass Road and Gillies Ave. NZTA announced in September 2010 that it was replacing the last three fords on SH 1S. The shingle fan fords are near Kaikōura, and while generally being dry, on about 28 days a year state highway traffic used to detour around them due to high water levels on old single-lane bridges, leading to delays on a major freight route. With the detour bridges reaching the end of their lifespan, NZTA replaced the fords with culverts. Route changes Motorway and expressway upgrades Construction of motorways and expressways has diverted the route of State Highway 1 in many places. The opening of the Auckland Harbour Bridge and the Auckland Northern Motorway between Northcote Road and Fanshawe Street in May 1959 saw State Highway 1 diverted from its former route around the Waitematā Harbour. Northern extensions of the motorway in 1969 (to Tristram Avenue), 1979 (to Sunset Road) and 1984 (to Dairy Flat Highway via Greville Road) diverted State Highway 1 off Wairau Road and Albany Highway. A motorway extension from Greville Road to Silverdale in 1999 bypassed Dairy Flat Highway, which was re-designated State Highway 17. In