Mr Hughes calculated a cyclist travelling at 12kmh (7.5mph) would take less than one second to pass over the markings. He said it looked like a cycle lane that was "probably the shortest one in Cardiff may even be the shortest one in Britain".
Cardiff council said the markings were too wide and would have to be reduced by around a half their current width to conform with the plans for them.
A spokesman said: "The road marking in the photograph forms part of a new contra flow cycling facility extending between Adam Street and Churchill Way via Sandon Street and Guildford Crescent.
"It will be particularly useful for cyclists accessing the city centre from the Splott and Adamsdown areas.
