Line 1 heading north from Yonge/Bloor is a really long trip. There's a lot of stops outside of stations going on on that line compared to line 2 imo. Those newer big trains are amazing tho, feels like they can hold more passengers?
The Toronto Rocket cars do have a larger capacity than the T1 cars currently run on the Bloor-Danforth line.
Just from what I notice is, Yonge/Bloor station gets really really busy. Dangerously crowded at times.
From Yonge/Bloor going east on line 2, a lot of travellers get off between Yonge/Bloor n Pape stations.
This is one of the major reasons for the original conception of a relief line. The 'purpose' of the Relief Line North and Relief Line South that was being worked on before the Ontario Line was to allow people from downtown to head east from Pape station on Line 2
without needing to transfer at Bloor-Yonge station. This would in theory reduce how busy Bloor-Yonge station would be, as some percentage heading east would instead take the Relief Line.
The Ontario Line at surface level is also supposed to solve a similar problem, but markedly has a longer alignment and more interchange stations with the GO train lines. This line in theory will still allow the transfer of people from downtown to east from Pape station on Line 2. From this thread there appears to be a lot of pushback on the Ontario Line, but it is important to not mistake this as being against transit in this corridor as a whole, but usually is due to disagreeing with one of the major decisions the new Ontario Line has changed from the older Relief Line South design.
What problems is any relief line suppose to solve ??
The main concern with the OL (in my opinion) is that the line is not going to use the same subway cars as either Line 2 or Line 1 (ie not the Toronto Rocket or the T1 cars). They would have a smaller capacity than the other subway lines, and may be more akin to the Eglinton Crosstown line. Allegedly the overall line capacity will be the same despite smaller cars by having more frequent trains, but this needs to be proven possible during the design phase. It will be interesting to see how this proceeds.
There also seems to be some opposition to the Ontario Line's focus on GO interchanges, which may be viewed as relieving the GO lines more than the original conception which focused in relieving Bloor-Yonge station. This may be a major disconnect for a lot of people and could be the reason you're asking "what problem is any relief line supposed to solve". It is difficult to say at this point whether adding relief to GO will also help with Line 2, whether GO Regional Express Rail is required to effectively reduce Line 2 congestion, and whether smaller trainsets are going to help in both the near-term and the far-term based on projected population growth.
A 'relief line' is usually pitched to relieve some kind of congestion on other lines in a transit system. Our main concern should always be if the new line will adequately reduce congestion. As it stands many people here do not believe the Ontario Line is adequate, for a variety of reasons.
and why does line 1 have so many interruptions?
Not really my area of expertise, perhaps someone else could shed some light on this