I just finished two trips, one from Portland to Seattle and one from Portland to Newport, OR on the coast. I recorded tracks from my GPS logger, and now I'm cleaning up the TIGER data for the covered areas.

Most of the trips were highway driving, which has given me some interesting insight into the TIGER data. The US Census Bureau documentation says that TIGER is a composite of multiple sources, and the highways show it.

US highway 20 in Oregon had some interesting artifacts. In Lincoln county, the way was a rough approximation of the road, with typical TIGER misalignment. As soon as it crossed into Benton county, the way was an exact match with the GPS track and the Yahoo aerial photos.

Interstate highway 5 in Washington state was interesting too. In Cowlitz county, I-5 was a single way with poor accuracy, but as soon as it crossed into Lewis county, it became dual ways with accurate placement. Based on the tiger:tlid tags, it looks like the dual ways were original Tiger data and not later OSM edits.

I expected that US highways and Interstate highways would be consistent for their whole length. But in retrospect, I imagine that not only do they export at county levels, much of the TIGER database was probably built by importing data at county level too.