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Here should be marked the exit "Piazza Mercator/Duomo" for the pedestrian tunnel: "Percorso meccanizzato Posterna - Piazza Campello".
Note, there are different names in different publications for this exit, such as 
"Via Saffi" (Wikipedia) or "Piazza F.LLI Bandieri" (map of emergency exits inside of the tunnel), whereas the overview map at the entry of tunnel says "Piazza Mercator/Duomo" 