The New York Observer ran a series of eight letters from October 11 until December 27, 1900 by a man named Augustus. He was reporting on the Paris Exposition and part two (October 18) includes a description of the "traveling sidewalk" in action.
From this part of the fair it is possible to proceed to a distant exhibition which is placed in what is called the Champs de-Mars, without going out of the gates, by means of a travelling sidewalk or a train of electric cars. Thousands avail themselves of these means of transportation. The former is a novelty. It consists of three elevated platforms, the first being stationary, the second moving at a moderate rate of speed, and the third at the rate of about six miles an hour. The moving sidewalks have upright posts with knobbed tops by which one can steady himself in passing to or from the platforms. There are occasional seats on these platforms, and the circuit of the Exposition can be made with rapidity and ease by this contrivance. It also affords a good deal of fun, for most of the visitors are unfamiliar with this mode of transit, and are awkward in its use. The platform runs constantly in one direction, and the electric cars in the opposite.
Below is a photo of the moving sidewalk from the Library of Congress as well as a German postcard (circa 1900) of the moving sidewalk concept.
Postcards Show the Year 2000 (circa 1900)