The code was written to accept serial input at any time before the intersection while the car is driving to tell it to either turn left, right or go straight, but the USB-Serial cord pulls the car to the left. Instead the direction to turn was uploaded before the car started driving.
The car required partially using many 9 V batteries since the sensors and motor don't function below 7.2 V.
The Adafruit & IR Sensor libraries helped to streamline the data measurements but the most complicated part of the project was figuring out the coding to make sure the car moved as expected under all conditions.
At larges distances between the RGB sensor and "traffic light" the ambient light background prevents the sensor from accurately determining the traffic light color.
For practical purposes, a self driving car would need an additional RGB sensor to measure the ambient light at the same time as observing the traffic light, especially since ambient light changes throughout the day.