The longest straightest stretch of road I've ever been on is Interstate 10 from Phoenix to Quartzsite Arizona. 129 miles.
The Pan American Highway which stretches from Alaska, through Canada and the US to Mexico, then all the way to Chile.
Note: the US is not the biggest country in the world.
I would definately say I-80. This hwy goes all the way from right about Peterson New Jersey to San Francisco California. From coast to coast, that's a long hwy!!
