Can you help me design a circuit diagram? Let the red, yellow and green lights blinking cycle, simulating traffic signals

Don't countdown and change the light flashing function, this circuit is very simple, as shown in

Change the capacitance can change the light time, transistor bias resistor to keep the same, change the collector current limiting resistor can change the brightness of the LED, it is important to note that the green LED light up voltage is more than in the 2.8-3.2V, red, yellow LED more than in the 1.8-2.2v, so the green light limiting resistor resistance should be changed to a smaller value. So the green current limiting resistor should be changed to a smaller value.