The closest to a credible source I found is this page:
Retro Futurism At Its Best: Designs and Tutorials — Smashing Magazine

Which links to a German page with Klaus Bürgle’s works, section “Städte & Verkehr I” (Cities & Traffic I), but I don’t see the image there. I also looked at the other Klaus Bürgle sections (I did not check all the other artists that appear there).

The source of the hi-res posted image, with no information, is:
…monorail | James Vaughan | Flickr

Seen on Dark Roasted Blend: One-Track Wonders: Early Monorails, which attempts to credit the image, but with broken links.

  • @TenderfootGungi
    3•1 year ago

    I have wondered just how fast a hanging monorail could safely go?

    • @[email protected]OP
      2•1 year ago

      safely

      That’s a huge restriction for a hanging monorail, hehe.

      More seriously, according to a google smart answer (shown on the search hanging monorail top speed):

      70 km/h
      CRRC Suspended Monorails
      The max. Speed of the train is 70 km/h, the fastest of its kind in China.

      Which points to this page Urban Monorails Trains:


      A prototype of suspended monorail train rolled out in CRRC Sifang recently. The max. Speed of the train is 70 km/h, the fastest of its kind in China. Driven by a permanent magnet motor, the experimental train runs along an overhead monorail.

      I don’t know if experimental implies that it’s not been tested enough, or that it may go faster when finished.