The bike lane (end of the "quality" bike corridor) on Mayfield Rd southbound ends about a hundred metres before the junction with Liberton Rd. It should extend up to the junction, and ideally continue through to Kirk Brae and Liberton Road.
Extending the bike lane would allow cyclists to pass the queuing cars and get to the traffic lights. At the moment, cyclists are stuck at the bottom of the steep hill at the end of the cycle lane, and then can cycle up only very slowly, with lot of angry car driver behind them. It often takes two green phases to get from the end of the cycle lane to the actual lights, unless you overtake on the right against oncoming traffic speeding around the corner from Liberton Rd.
This is a key junction as there are no other routes between KB and Liberton/Gilmerton (except going around to Cameron Toll which is not much better).