In an area that was once coal rich, to now having a green bridge -- guess they are trying to make a statement.

They have even put up wording on the westbound side under the bridge which reads

          Born from the origins of "Hope under Dinmore"
and surrounded by the Warrego, Ipswich, and Cunningham,
       Dinmore rests peacefully as the gateway to the city.

Please replace the cache where you found it

You will need stealth and a pen