The sequence of events leading to the outage began around 3am (local time) on 28 September 2003, when the 400 kV Lukmanier powerline between Mettlen and Lavorgo arced to a nearby tree and automatically disabled itself.
[1]: 4 Those circuits could only stably carry the current for approximately 15 mins, but the Swiss control room operator was not aware of the urgency.
7.5 GW of distributed power plants from the grid and the under-voltage load shedding (UVLS) could not compensate (cf.
figure "Frequency behavior in Italy in the transitory period", UCTE report, April 2004, p. 115[1]).
Thus, many people were on the streets and all public transportation were still operating at the time of the blackout (at about 3:00 on 28 September 2003) despite the fact that it was very late at night.
The final report of the investigation committee on the 28 September 2003 blackout in Italy was published in April 2004 by UCTE.