We have tried GMRS traveling with some friends in separate vehicles. Marginal at best. Cell phone is much better for talking to family/friends when in separate vehicles. But if cell service is not available, GMRS can work. CB can work also, but best to do it on something other than channel 19.
If you just want to be able to converse with anyone along the highway then CB is the best option as not many use GMRS for that purpose due to limited distance. But, you have to put up with the trash talking you will hear there. Much is not suitable for sensitive ears, and certainly not for children. But can be very handy to find out road conditions ahead, or why traffic is stopped in front of you in the middle of nowhere as far as you can see.