Coming from Japan, the most frustrating aspect of Acela is that it routinely runs late, due to having to share tracks with those damned freighter trains. The Shinkansen's average delay is measured in seconds; the Japanese routinely plan trips with 5 minute transit time because they can trust the trains to arrive on time.
The main reason Shinkansen trains are fast and on time is because the main routes run on dedicated tracks. On the Yamagata and Akita lines, they do share tracks with local passenger trains, but Shinkansen gets preferred right-of-way.
This, incidentally, is why splitting track and train ownership is a bad idea for high speed rail. Neither side can take full ownership in assuring the most convenience to the end users, which is what generates revenue at the end of the day.
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