![factorio bus factorio bus](https://i.redd.it/46wew0my5fy21.png)
On a 4 belt line, you need to make sure the furthest belt from the split can feed into the edge you split from.
![factorio bus factorio bus](https://i.imgur.com/62fmaHR.jpg)
On a two-belt line, (like steel or plastic), use a regular splitter. Balance After you split off to the side, you will need to balance the belts again to feed more back to the lane you just took from.