Let's see, driving 70 mph saves you about 15% in time over 60 mph. So, you drive across the entire state of Texas from Texarkana to El Paso (about 800 miles) at 70 mph. It will take you about 11 hours and 30 minutes with no stops. But, slowing down to 60 mph it will take you about 13 hours and 15 minutes. Now add fuel stops, food stops and rest stops and that probably adds a couple of hours to either trip. So, now we're at 15.25 hours vs 13.5 hours.
Now consider the increased possibility of being delayed due to a tire failure plus the increase in fuel costs.
Just what is 2 hours and 15 minutes worth?