I drive commuter trains around Sydney every day... many of the lines I've been GPS tracing recently and this works fine as long as you are above-ground. The challenge now is to get a better alignment of Sydney's underground rail lines.

This week my focus was on the Eastern Suburbs Rail line (ESR) between Erskineville and Bondi Junction. Large parts of it are underground, and the estimated tunnel routes shown on OSM just weren't matching with what I was experiencing as a driver at the front of the train.

So how do we fix this?

My initial thoughts were to make a rough sketch as I drove along. With experience I've become very good at judging distance ahead of me in measures of train-length due to the number of instances where I have to restrict my speed (e.g. going across a set of points - or a turnout) until the entire train has passed the risk. I do this by judging an imaginary point ahead of me as being my train length, and when I reach that point I can resume speed. All the trains I drive are 8 cars long (about 160m in total), so I could say for example, the track continues straight for 2 train lengths, then a gentle left curve for 3 train lengths, immediately followed by a hard right curve for half a train length.

But my sketch idea didn't work. I simply couldn't get everything onto paper that I needed as well as drive the train. It just wasn't practical - so this week I tried the Voice Recorder on my iPhone and verbalized everything I experienced as I drove through the tunnels. This gave me some really useful data which I was able to use to fine-tune the alignment of the underground sections of Sydney's Eastern Suburbs line on OSM.

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Re-awakening my interest in OSM. On the surface it seems like so much has already been done, but digging deeper there is always more to do. As a train driver I have a lot of knowledge about the CityRail system so that might seem a logical start - then again, do I want to dwell on work during my leisure time?