In late 2009, it was announced that due to greater than expected complexity of the task and increasing material costs for the 920 tons of reinforcing material instead of the approximately half amount of that originally envisaged, clip-on maintenance costs had increased by a further NZ$41 million. NZTA noted that the clip-ons would not be able to be strengthened again after the current works were finished. However, after completion of the upgrade, the bridge would have a further life of between 20 and 40 years if truck restrictions were reintroduced in 10–20 years on the northbound clip-on. A "tidal flow" system is in place, with the direction of the two centre lanes changed to provide an additional lane for peak-period traffic. During the morning peak, five of the eight lanes are for southbound traffic; in the afternoon, five lanes are northbound. At other times, the lanes are split evenly, but peak traffic has become proportionately less – in 1991 there was often a higher than 3:1 difference in directional traffic; in 2006, this had dropped to around 1.6:1. The bridge has an estimated capacity of 180,000 vehicles per day, and in 2006 had an average volume of 168,754 vehicles per day (up from 122,000 in 1991). In March 1982, the Ministry of Transport and Auckland Harbour Bridge Authority conducted a week-long traffic blitz in an attempt to improve the standard of driving. Of the 600,000 vehicles which used the bridge over this period, 6,000 were stopped, with half of those receiving a ticket and the rest cautioned. A second blitz was held for 36 hours a few weeks later. For many years, lane directions were indicated by overhead signals. In the late 1980s, a number of fatal head-on accidents occurred when vehicles crossed lane markings into the path of oncoming traffic. In 1990, a movable concrete safety barrier was put in place to separate traffic heading in opposite directions and eliminate head-on accidents. Two specially designed barrier transfer machines moved the barrier by one lane four times a day, at a speed of 6 km/h. It took 40 minutes to move the barrier, which was the first of its kind in the world. In March 2009, the barrier transfer machines, which had lasted four times their original design life of five years, and the barrier were replaced. The new machines are capable of moving the barrier in half the time the old machines did. The concrete barrier blocks and the metal expansion blocks have been reduced in width by 200 mm, giving more width in the lanes either side of the barrier.