Hi there! Marked by a single yellow line is a normal bus lanes reserved solely for approved vehicles during peak hours with periods in between for normal motorists use. The operating hours will be from Monday to Friday at 7.30am - 9.30am & 5pm - 8pm.
Meanwhile, marked with yellow and red line are a full-day bus lane with the same purpose. However it operates throughout the morning peak hour to evening peak hour without the period in between: Monday to Saturday from 7.30am - 11pm.
To find out more about the bus lane laws, you can read the full article here: https://www.motorist.sg/article/6/singapore-bus-lane-laws-and-fines