When the petrol tax was introduced in1927 it was worth approx. 50 cents in todays money, This was only sufficient to meet half the costs of Main (now State) Highways. It provided no money for local roads.
In 1930 the tax was increased to 75 cents to meet three-quarters of the costs of main highways.
In 1936 the Main Highways Fund was made liable for the entire cost of State Highways. The only increase in funds came from traffic growth despite the fact that traffic growth directly increases costs on gravel roads. Less than one-quarter of the highways had been tarsealed.

In 1954 the addtional petrol taxes added for the Consolidated Fund during the depression and World War II were finally payed into the new National Road Fund. This was done to overcome 100% inflation since 1929. An additional 50% was added to the petrol tax to assist with local roads because most were now carrying a lot of through traffic.

Unfortunately Parliament lacked the wisdom to index the petrol tax to inflation which would have prevented a repeat of the cronic underfunding after World War II. This lack of wisdom has deprived the road fund of $60,000,000,000 in revenue. Even this amount of money would not have been sufficient to build the best roads in the world. But it would have come close.

$30,000,000,000 would have been sufficient to build divided highways on the easiest two-thirds of the terrain between our major cities.

The remaining $30,000,000,000 would have been sufficient to acheive the same level of safety as B-roads and two lane A-roads in Britain and their equivalents in most European countries. The major safety defficiencies in our roads are not the width or geometry of the tarseal. In fact almost our entire roading investment in the last 80 years has been spent improving these two factors. What we haven't spent any money on is upgrading our roadsides to cater for the demands of motor traffic instead of horse-drawn traffic. Next time you watch Top Gear, 5th Gear or Auto Motor Und Sport pay attention to the roadsides. Do you see lots of power poles right next to the tarseal, fence posts as solid as tree stumps, deep ditches or steep drop-offs without safety barriers? However, there is one often overlooked aspect of road geometry that is inevitable when not enough money is available: inconsistent curve design from one curve to the next, which is actually made worse if the black spot approach is allowed to replace the black route approach rather than complementing it.

So, with 60,000,000,000 needed to build the best roads in the world, not including higher environmental and seismic standards, it will take 100 years to acheive this feat using only the $600,000,000 that the government takes each year to fund it's deficit.