Difference between German Regional Express and Regional Bahn

The difference between regional railway lines (RB = Regionalbahn) and regional express lines (RE = Regionalexpress) can lie, for example, in the stops approached, the travel speed, the length of the route and the seats offered.

Typically, a regional express runs on longer routes and, in contrast to the regional train, stops at fewer stations. This, and sometimes the use of other vehicles, results in a higher average speed. At the same time, longer trains and larger wagons with a larger passenger capacity are often used on RE lines than is the case with RB lines.

Your observation that both types of trains often drive on the same routes and have the same stops is typical, for example, in metropolitan areas where there are many "important" stops. It is often the case that in metropolitan areas RE and RB share the same routes and travel at the same speed, but the route changes when leaving the metropolitan area and the RE line begins to skip stations while the RB line is still approaching the stations.

It is similar on some ICE routes. In metropolitan areas such as the Ruhr Area, the ICE will hardly be faster than an RE or RB and also serve the same train stations. The speed advantage only becomes apparent over long distances overland.
2021-03-23 at 00:34