The Null Device
An Australian human-interface innovation I hadn't heard of until now: the Marshalite
, an early analogue traffic signal developed in the 1930s. Unlike modern pedestrian crossings (with the exception of those in some US cities), it not only displayed whether crossing the road was permitted, but gave an indication of how much time pedestrians had to cross, in the form of a clock face. The downside of the Marshalite was that, being mechanical, it was not adjustable, and worked on the assumption that traffic lights had a fixed duration. (And changing the speed of the moving hands is not an option; people would make assumptions about what the hand at a specific position would mean, and could not be expected to look at it long enough to gauge the speed.) At some point, they started adjusting the lengths of traffic lights to better manage traffic, and the Marshalites were all replaced by the now ubiquitous red/green man.
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