It is. Car conversations are a serious issue with respect to distracted driving. I personally can't handle thinking about driving safely and thinking about a conversation. Humans are famously bad at multi-tasking and I don't see how being in a car gives us magical powers.

I thought I had read a study about talking to people in your car versus drinking, but here's a similar one with talking on a phone versus being drunk: https://www.ncbi.nlm.nih.gov/m/pubmed/16884056/