I live in Amarillo. I’ve lived here 15 years. All these years there has been no direct exit from I-40 Westbound to I-27 south without going through local streets. This is now being corrected and the entire area around I-40 and I-27 south (I-27 begins in Amarillo and ends in Lubbock, TX) is under massive construction.
That being said, and knowing there are ways to drive around this area without getting on an Interstate, Amarillo only takes 15 minutes to drive from east to west on the highway in normal conditions.
The worst of Amarillo traffic is a good day in any other city in Texas.
However, the busiest street in Amarillo during the morning and evening rush is Coulter Street, which starts from the north by two major hospitals, Northwest Texas Healthcare System, and BSA – Babtist Saint Anthony health care system. Besides these two excellent, huge and major hospitals, there are dozens of other medical facilities nearby, plus motels, Waffle House, the Cinema, etc. It can be busy with lots of lights during rush hour. Further south on Coulter you’ll find many shopping areas, a bank or two and even a Walmart. You will be okay, though. Nothing like what you might experience in bigger cities.