The total length of tunnels in the Loop is 12 km (7.5 mi) with 10 km (6.2 mi) of circular tunnels, and 2 km (1.2 mi) of box tunnels.
The four tunnels have an average length of 3.74 km (2.32 mi), with a further kilometre of track connecting with surface tracks.
Some 900,000 m³ (1,200,000 cu yd) of earth was removed and 300,000 m³ (390,000 cu yd) of concrete poured to form the stations and line the tunnel walls.
30,000 tonnes (33,000 short tons) of steel reinforcement were used, with another 10,000 tonnes (11,000 short tons) used temporarily during construction.

The General Manager and Chief Engineer of MURLA, Frank Watson liaised closely with the engineers working on Sydney's Eastern Suburbs Railway and was struck by their 'degree of unpreparednesses' and sought to improve on the contemporary project.
The 'double sleeper' floating track system used solved the problem of ground transmitted vibration and track noise, and the loop has some of the best designed and quietest underground stations in the world.
At the time of construction Parliament station had the Southern Hemisphere's longest escalators.

In 1965, the cost of the project had been estimated at between £30 and £35 million, by 1975 high inflation had resulted in it rising to $255,600,000.
While the final cost was $500 million, it resulted in the reversal of a 30-year trend of falling suburban rail patronage.
The total length of tunnels in the Loop is 12 km (7.5 mi) with 10 km (6.2 mi) of circular tunnels, and 2 km (1.2 mi) of box tunnels. The four tunnels have an average length of 3.74 km (2.32 mi), with a further kilometre of track connecting with surface tracks. Some 900,000 m³ (1,200,000 cu yd) of earth was removed and 300,000 m³ (390,000 cu yd) of concrete poured to form the stations and line the tunnel walls. 30,000 tonnes (33,000 short tons) of steel reinforcement were used, with another 10,000 tonnes (11,000 short tons) used temporarily during construction.
The General Manager and Chief Engineer of MURLA, Frank Watson liaised closely with the engineers working on Sydney's Eastern Suburbs Railway and was struck by their 'degree of unpreparednesses' and sought to improve on the contemporary project. The 'double sleeper' floating track system used solved the problem of ground transmitted vibration and track noise, and the loop has some of the best designed and quietest underground stations in the world. At the time of construction Parliament station had the Southern Hemisphere's longest escalators.
In 1965, the cost of the project had been estimated at between £30 and £35 million, by 1975 high inflation had resulted in it rising to $255,600,000. While the final cost was $500 million, it resulted in the reversal of a 30-year trend of falling suburban rail patronage.
City Loop