It does sound reasonable if most people know where their turn is, start planning for their turn far in advance and take some time to coast before starting to brake. That’s probably what the group who wrote the law was thinking. It is not how people actually drive and it’s too far in excess of what following traffic needs to exercise caution or slow down.

One of the challenges of traffic planning is that people will do what feels comfortable and is working; it’s not really worth writing laws to force them out of that unless there’s an oil crisis or a municipal revenue crisis.