Editing Line 1 Yonge–University (section)

===Capacity constraints===
{{update section|date=March 2024}}
Toronto council approved the plan in principle in January 2009 provided there were upgrades to the existing line to support the additional ridership from York Region.<ref name="NP-2009-02-18">{{cite news |last=Haynes |first=Allison |date=January 6, 2009 |title=City's Demands Push Price Of Subway To $5B |url=https://nationalpost.com/news/canada/toronto/story.html?id=1146889 |newspaper=National Post |location=[[Toronto]], [[Ontario]], Canada}}{{dead link|date=August 2016|bot=medic}}{{cbignore|bot=medic}}</ref> Specifically, Toronto politicians stated that the Yonge line does not have the capacity to support an extension to Richmond Hill until a separate relief line is built between Pape and Osgoode stations. In the morning rush hours, southbound trains on the Yonge line usually reach capacity between York Mills and Eglinton stations.<ref name="TheStar-2016-03-03" />

In March 2016, York Region officials stated their belief that SmartTrack, [[GO Expansion|electrified GO service]], the Spadina subway extension and [[automatic train control]] would be implemented by 2026 and be sufficient to support the extra ridership of an extension to Richmond Hill. Thus, the deputy mayor of Richmond Hill wanted to start construction of the extension by 2019.<ref name="TheStar-2016-03-03" /> Vaughan politicians and officials noted a June 2015 Metrolinx report which indicated the Yonge line would have enough capacity to carry the new demand if the Spadina extension and [[GO Transit Regional Express Rail|Regional Express Rail]]<!--Don't bypass redirect per [[WP:NOTBROKEN]]--> on the Richmond Hill line were implemented.<ref name="TheStar-2016-03-03a">{{cite news |url=https://www.thestar.com/news/gta/transportation/2016/03/03/vaughan-councillor-challenges-yonge-subway-no-capacity-mythology.html |title=Vaughan councillor challenges Yonge subway 'no-capacity mythology' |newspaper=[[Toronto Star]] |first=Tess |last=Kalinowski |date=March 3, 2016 |access-date=June 9, 2016 |archive-date=August 5, 2016 |archive-url=https://web.archive.org/web/20160805225857/https://www.thestar.com/news/gta/transportation/2016/03/03/vaughan-councillor-challenges-yonge-subway-no-capacity-mythology.html |url-status=live }}</ref><ref name="ML-2015-06-25">{{cite web |url=http://www.metrolinx.com/en/docs/pdf/board_agenda/20150625/2015-06-25_Yonge_Relief_Network_Study.pdf |title=Yonge Relief Network Study |publisher=[[Metrolinx]] |first1=Leslie |last1=Woo |first2=Anna |last2=Pace |date=June 25, 2015 |access-date=June 9, 2016 |archive-date=March 13, 2018 |archive-url=https://web.archive.org/web/20180313120745/http://www.metrolinx.com/en/docs/pdf/board_agenda/20150625/2015-06-25_Yonge_Relief_Network_Study.pdf |url-status=live }}</ref> However, Metrolinx has no immediate plans to provide electrified GO service on the Richmond Hill line and Toronto transit advocate [[Steve Munro]] noted that the line would be at 96 percent capacity in the peak hour and there would be some overcrowding due to variations in traffic over the hour.<ref name="TheStar-2015-04-17">{{cite news |url=https://www.thestar.com/news/gta/transportation/2015/04/17/go-to-add-30-per-cent-more-trains-in-next-5-years-s.html |title=GO to add almost 50 per cent more trains in next 5 years |newspaper=[[Toronto Star]] |first=Tess |last=Kalinowski |date=April 17, 2015 |access-date=March 30, 2016 |archive-date=March 7, 2016 |archive-url=https://web.archive.org/web/20160307142352/http://www.thestar.com/news/gta/transportation/2015/04/17/go-to-add-30-per-cent-more-trains-in-next-5-years-s.html |url-status=live }}</ref><ref name="SteveMunro-2016-07-05">{{cite web |url=https://stevemunro.ca/2016/07/05/york-region-wants-a-subway-overstates-available-capacity/ |title=York Region Wants a Subway, Overstates Available Capacity |first=Steve |last=Munro |author-link=Steve Munro |date=July 5, 2016 |access-date=July 11, 2016 |archive-date=September 21, 2016 |archive-url=https://web.archive.org/web/20160921221326/https://stevemunro.ca/2016/07/05/york-region-wants-a-subway-overstates-available-capacity/ |url-status=live }}</ref>

In March 2016, the Toronto mayor's office said that [[SmartTrack]] and automatic train control may have also been required, which was reaffirmed by TTC spokesperson Brad Ross that June.<ref name="TheStar-2016-03-03" /><ref name="TheStar-2016-06-02" /> This was affirmed again by Metrolinx in January 2019, thus reversing its opinion in its June 2015 report. The 2019 report also predicted that if both phase 1 of the then-planned [[Relief Line (Toronto)|Relief Line]] to Pape station and the Yonge North extension had been built, Line 1 would have been over capacity by 2041. At that point, the Relief Line would have needed to be extended farther north.<ref name="TheStar-2019-01-31">{{cite news |url=https://www.thestar.com/news/gta/2019/01/31/relief-line-must-open-before-yonge-north-subway-extension-says-metrolinx.html |title=Relief Line must open before Yonge North subway extension, says Metrolinx |newspaper=[[Toronto Star]] |first=Ben |last=Spurr |date=January 31, 2019 |access-date=January 31, 2019 |archive-date=February 1, 2019 |archive-url=https://web.archive.org/web/20190201040208/https://www.thestar.com/news/gta/2019/01/31/relief-line-must-open-before-yonge-north-subway-extension-says-metrolinx.html |url-status=live }}</ref> However, the Relief Line was later replaced by the [[Ontario Line]], which will run to Eglinton Avenue at [[Don Valley station]] to meet with Line 5 Eglinton.