When this happened to me with my TGV service, I had to increase frequency (cut down to the 200kph trains you mention) and also the bus feeders seem to work best at 60seconds or less frequency in my experience. Also, where I had to look was at traffic inside the city. This same traffic jam was killing my bus/tram routes. So add bus lanes, create diversion roads for cars, etc. you need to make sure your feeder system flows and flows quickly.