Source: Wikipedia France
Author: Chris93
Licence: CC BY-SA 4.0

Perhaps a world record was broken here: the line operated for seven years between 1993 and 1999 without having carrying passengers.
The idea was to connect a metro station with a commercial centre — which happened. That trading centre went bankrupt even before the line opened and nothing came in its place: so after 6 years, patience (and money) ran out...