ShaneThe NWRL trains have emergency exits both ends for the tunnels but also have the walkway for when they are elevated.Hi
An engineer suggested it was so maintenance workers could walk along it to which another person responded saying it was so 19th century.
I just looked up the Dubai metro and it goes above ground too so the same problem as the NWRL
(in friendly tone) How is the platform "so 19th century"? You have the space in the tunnel, so why not?
Also remember that if the line has track based power supply then this keep people away from things that go zap! But yes Sydney is using O/head.
I guess it is horses for courses, if the land is cheap and subject to flood then it is probably cheaper to have a section above ground as is the NWRL but this would mean you are limited to 3.4m wide trains so as you say if the space is there in the tunnels and with cross passages every 250m I suppose there is every chance of safely using the walkway.
However with hard rock TBM getting better every year https://www.tunneltalk.com/China-22Feb2018-Robbins-main-beam-gripper-TBM-breaking-records-in-China.php I believe the metro west would be best a stand alone tunnel which then would allow a high capacity train https://3dwarehouse.sketchup.com/model/331a49f3-7949-495b-b3d9-e675231588d6/5-metre-wide-carriage also if an access/recovery/lift shaft was started now on the grass next to Central it would eliminate the need for an expensive concourse as people would just walk along the metro west platform.
Regards the zap you will notice the wide carriages have only four wheels and are pulled and pushed by two 100t driverless battery powered locos that would be charged off peak.