The group has a group leader and a sweeper (the last man).
When the group leader comes to a crossroads where the route selection is not known to the group, he gives a sign to rider number two who moves to the side of the road and stays in the driving direction. The group leader keeps riding. As the rest of the group pass rider number two, he shows them which direction they will go. When the sweeper gets close, rider number two starts moving again hence the sweeper will always be the last rider of the group.

When the next crossing approaches, the group leader signs to the new rider number two to wait for the sweeper, etc. In this way the pace and flow will be much better because only one person needs to stop at intersections, while the others keep moving. In addition, group participants get to change positions in the group. The group leader do stop at times, to regroup or when a short break is needed (or maybe to admire the view and to take a photo). The sweeper can be replaced occasionally so that noone need to have this task for the entire ride. Conversely, the group leader is always the same.

A problem that can occur when something happens at the back of the group, such as a puncture, is that the tour guide may go some distance before he realises there are no more "corner-men" behind him. The following is a good solution:
When something goes wrong, the group should designate a messenger as soon as possible. The messenger drives toward the group leader and along the way informs all the "corner-men" of what has happened. All "corner-men" stay at their intersection until the tour leader and messenger return, and then join them riding back to "whatever went wrong".
This way, there is less chance that the tour guide has to stress-ride back having lost parts of the group.

In the case of smaller groups, we can also ride with a "floating" sweeper.
The difference is that the "corner-man" becomes the sweeper as the last rider passes by.
This requires, however, that everyone can count and nobody's going to drive off until the last rider has passed, which is not so easy at all times;)
We explain properly before the trip departure and choose the system that fits best for each group.