In order that planning may be integrated more closely with transport needs the National Roads Board conducts traffic counts on all main routes at regular intervals, when the number of cars, as well as the number and weights of heavy vehicles, is recorded. The bulk of the traffic is local but on some of the major or arterial routes, through traffic is increasing to such an extent that by-pass roads have become desirable. Traffic counts taken on city streets usually show greater density than do those on nearby rural highways. Normally the pattern shows a marked increase as the road enters an urban area and a corresponding decrease as it leaves.
Recent traffic counts taken on the Auckland-Wellington main route give the following figures: at the south end of the Auckland Motorway density reaches 17,000 vehicles per day, falling to 2,800 south of Mercer and increasing again to 6,000 between Ngaruawahia and Hamilton. Between Hamilton and Cambridge the traffic averages 4,500 vehicles per day; on the Desert Road, 500; at Himatangi, 2,800; and north of Paekakariki, 6,100 vehicles per day. The Hutt Road, which connects the Hutt Valley with Wellington city, carries up to 30,000 vehicles per day. This is the densest traffic, outside city limits, on any road in New Zealand.
The traffic density in the South Island is generally much lighter than in the North. On the main route from Picton to Bluff the average varies considerably. Between Picton and Blenheim it is 1,400 vehicles per day; at Kaikoura, 400 vehicles per day; at Waimakariri Bridge, north of Christchurch, it is 6,500; at the Rakaia Bridge, 2,200; and north of Oamaru it drops to 1,000 vehicles per day At Milton, south of Dunedin, the average rises to 1,800 vehicles per day, while between Invercargill and Bluff it drops again to 1,400.
The situation in the larger cities is as follows. In Auckland, on the Great North Road just north of Point Chevalier Road, and also on Broadway in Newmarket, traffic density varies from 25,000 to 30,000 vehicles per day. In Wellington the traffic density south of Ngauranga is about 28,000 vehicles per day, increasing to 33,000 vehicles south of Ngaio Gorge. Waterloo Quay, north of Bunny Street, carries about 25,000 vehicles per day. In Christchurch the traffic in Blenheim Road is about 10,000 vehicles per day and the lower end of Papanui Road about 15,000 vehicles per day. In Dunedin trafic is about 20,000–25,000 vehicels per day along the Anderson's Bay Road, south of Cumberland Street, while the Main South Road in Caversham carries 10,000–12,000 vehicles per day.