My question applies to circumstances in which one is driving an extended distance by oneself. They also apply primarily--though not exclusively--to people who do not have the Tefilos HaDerech memorized, or whose minhag is to daven in front of a text at all times (i.e., Chabad).
One is supposed to say Tefilos haDerech while on the road. (Source: http://www.chaburas.org/derech.html). Presumably, attempting to say the prayer while actually driving would be prohibited for reasons of pikuach nefesh and kavana. The other options are to pull over, and say the prayer while stopped on the shoulder (i.e., of the highway), or to leave the highway and say the prayer at a rest stop or somewhere off an exit. However, both these options would seem to have problems. The first (stopping on the shoulder) seems like it could still be quite dangerous, especially for visibility reasons at night, or in bad weather conditions. The second is not always practical, and I am not 100% sure whether it would fall under the halacha of literally being on the road.
So, how, when, and where should one say this prayer?