The half cloverleaf is, also known as a trumpet interchange, as its name suggests, half of a Cloverleaf junction. Trains have to do some looping.

Half Cloverleaf Junction

Half cloverleaf junction with only 1 loop

Pros

• Can handle a large number of trains at a time.
• Traffic jams not likely.

Cons

• Trains must slow down to climb a slope.
• Trains join the main line before leaving. This could cause traffic problems. (Not applicable to the 1 loop design)
• Trains must turn left to go right. This could lead to trains getting lost. (Can be fixed by using waypoints). This is no longer an issue with newer OpenTTD versions that use a more advanced pathfinder.

Tips

• Make the loops bigger and without sharp turns.
• Make one of the loops go the other direction, so the train doesn't have to loop around.
• Make the branches bigger to hold a complete train, so trains that are waiting at a red signal aren't blocking other trains.