Radio shows are almost universally made to be randomly tuned in and out, whereas books are written under the assumption that you never skip a line, pausing and

Radio shows are almost universally made to be randomly tuned in and out, whereas books are written under the assumption that you never skip a line, pausing and even re-reading as necessary. Audiobooks are sitting in an awkward position between them, carrying over all the assumptions of the printed book into a medium of forced time. This is very similar to how talking to someone in the car is much less distracting than taking on hands-free: even the worst passenger will take more cues from the traffic situation about when it's ok to talk, when not to expect an immediate reply and so on than someone behind a phone line. Sure, an audiobook is less bad than many other driving distractions, but still a whole different league than radio (and also many podcasts I guess).