The diagram above illustrates and compares two sets of tunnels in two Australian cities based on construction time, cost, depth, and materials used. Looking at the diagram, it can be seen that the lower tunnel is deeper, more expensive, and was built faster than the upper tunnel. In addition, the lower tunnel is built from rock and clay while the upper tunnel is made from sand only. Although the length of the tunnels is not mentioned, but the diagrams suggest a difference in scale.
Firstly, in terms of the comparison between construction time and construction costs, the construction of the first tunnel began in 1986 and was completed in 1998, a total of 12 years of construction at a cost of $555 million. On the contrary, the second tunnel took just four years to complete (from 2002 to 2006) at a total cost of $1.1 billion USD. So, although the second tunnel was built faster, it cost twice as much as the first tunnel. Secondly, in terms of depth and materials used, the First Tunnel is 1.5 meters underground and is made of sand. The Second Tunnel is 2.5 meters underground and is made of rock and clay. Therefore, the Second Tunnel was built deeper and with more durable materials. Finally, in terms of structure and scale, both tunnels have 2 lanes running in both directions and the diagram shows that the second tunnel has a larger traffic volume, reflecting better service capacity.
In conclusion, the second tunnel is more modern with higher cost but shorter construction time, while the depth and construction materials are different, suggesting that the second tunnel may be more durable. In addition, the traffic volume in the second tunnel appears to be higher.