While the Interstate system is fantastic it also "killed" many small towns. The US highways ran through each one. 1
My daughter was living in Portlandia. The last time we were visiting and on the 101 the traffic was very heavy. 2 I am not a traffic person. But the portion of the 101 I have traveled is a beautiful drive. 3
1 Tis true to some degree. The idea of the Interstate system was to be high speed arteries where drivers - cars, truck, military convoys - didn't have to slow down to go through every town. But some towns have Interstates right on their outskirts - e.g. Woodland and Dunnigan on I-5 and Davis, Vacaville, Fairfield, and Dixon on I-80.
2 The freeway through Portland is I-5. US 101 goes through Astoria, on the coast. In large cities and metro areas freeways, including Interstates, often have not kept pace with population/traffic growth. In CA that is often intentional, and much of the taxes/fees that are supposed to go to building and maintaining highways get diverted to mass transit boondoggles and to band-aid budget deficits.
3 For most of the length of CA - from LA to Eureka - US 101 follows the path of the Spanish missions through the Coast Range Mountains. But at Eureka US 101 starts following along the coast. For most of the distance of US 101 where it goes through the Coast Range State Highway 1 ("Pacific Coast Highway" or "PCH") follows the CA coast. Whether SR1 or US 101, both are pretty beautiful drives.