On club group hikes I participate in, we stop periodically and wait for the slower hikers to catch up. Then of course the faster ones immediately take off as they have been resting for a bit, once again leaving the slower ones in the dust. But at least we know everyone is still with us.
(I should note that as a group, we have over 100 years of White mountain experience and maybe 200 if we have a good turn out. So, leaving the slower ones behind a bit isn't much of a concern. Being a small community, we know each others abilities pretty well and who might need some extra attention.)
If there is a trail junction, we all stop until the group is whole again. (road crossing in your case) We typically climb to a scenic vista and eat lunch there, which is another place we all meet up. (You could use a mid point shelter for this) On the way down, one of the stronger hikers follows in the rear behind the slowest hiker. None of us are very young and some are getting to their limits of ability. These hikes are in the White mountains and can be pretty strenuous.