Those travelling into Belfast city centre on Sunday have been told to make allowances for delays due to a number of marches taking place.
The second rally is expected to involve several thousand people from midday until later in the afternoon.
Diversions will be in place from around 11am.
A PSNI spokesman said: "Some traffic disruption is expected from 11am to 2.30pm today in Belfast city centre due to a number of parades and an event outside Belfast City Hall.
"Please allow extra time for your journey. Arterial routes will remain open; alternative routes will be made available."
Crowds are gathering from three points at midday:
1. McGurk's Bar Memorial, North Queen Street
2. Divis Tower, Divis Street
3. Cromac Square
They will then make their way to Belfast City Hall for a rally.
The last Time for Truth march saw over 7000 take part, organisers said.
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