504A King passes the Roncesvalles Carhouse as it approaches Queen Street West and the Queensway.

Continuing further east to Bathurst Street, the 504 enters a transit mall where automobiles have restrictions so as not to impede streetcar service.

[6][7] Between 2009 and 2011,[8] Roncesvalles Avenue was rebuilt to a new design, which included the addition of bike lanes and a widened sidewalk "bumpout" at stops to allow riders to board streetcars directly from the curb.

[9][10] However, the platform height at the bumpouts was incompatible with the wheelchair ramp on the low-floor Flexity Outlook streetcars that were introduced in 2018 on the 504 King route.

This plan was rejected[16] in favour of ordering brand-new, longer Flexity Outlook vehicles.

The 514 route increased capacity along the King Street corridor to address the growing downtown ridership.

[17] From December 2, 2017, the TTC assigned a minimum of two low-floor accessible Flexity Outlook streetcars on 504 King to handle weekday overcrowding, as the King Street Pilot Project improved service performance and made the service more popular.

Thus, the TTC designated the route as accessible except along Roncesvalles Avenue where the platform height still needed to be adjusted to allow deployment of the Flexity ramp.

[20] On May 9, 2021, the intersection of King Street, Queen Street, The Queensway and Roncesvalles Avenue (KQQR) closed due to various construction projects in the area such as track replacement, reconfiguration of the KQQR intersection, adjusting the height of streetcar loading platforms along Roncesvalles Avenue and upgrades to water, sewer and electrical infrastructure.

Initially, 504A King service was diverted to Dufferin Gate Loop instead of Dundas West station.

The 304 route was eliminated in February 1992, with the Broadview and Roncesvalles segments replaced by portions of other Blue Night bus routes; however, King Street remained unserviced directly until September 6, 2015, when the 304 King was restored as part of a $95-million investment from Toronto City Council.