。
The train departed on schedule.
Literal
Train [topic-は] on-scheduled-time [adverbial-に] departed.
A plain declarative sentence. 定刻通りに ('according to the scheduled time') is a fixed adverbial phrase built on 通り ('in accordance with'). 出発する ('to depart') is the formal/Sino-Japanese verb for trains and ships leaving. Note the subtle plain/polite tonal mix: 出発した is plain past, signaling written narration rather than dialogue.