Moderator: OpenTTD Developers
- Transport Coordinator
- Posts: 306
- Joined: 11 Aug 2019 18:15
- Location: Massachusetts, USA
The whole “path signals are more CPU intensive” is not true. As explained to me by the developer who wrote the pathfinder code: every time a vehicle comes to a junction the pathfinder must be run to determine the train’s route. With block and pre-signals, the train determines its own route. With path signals, the signal decides. Either way the pathfinder is called.
If there are no junctions before the next signal, the path signal just checks if the track is clear, working the same way as a block signal with no extra processing.
Regarding mixing signals: There is no performance impact to use one signal over the other or mixing them, but there is a risk if a junction has both block and path signal entries, which might result in trains crashing into each other. Block signals will just show green if there is no train in the block but not reserve a path if a train passes, while a path signal will go green if a path can be reserved to the next signal. As the block signal does not reserve a path, the path signal thinks the path will be free while it actually is a collision course with a train that entered earlier through a block signal. As a rule, always use the same signal type on all entries of that junction.
Most often, you will be fine with path signals on a junction as they allow multiple trains to enter the junction at the same time as long as their paths to the next signal do not intersect. For straight tracks it is just personal preference, although I have the idea that block signals allow slightly higher throughputs because they go green as soon as a train clears the next signal while path signals also seem to reserve the tile with the next signal resulting in a slightly longer signal block. For multi-platform straight through stations, you might need to look at presignal setups to force trains to go to empty platforms, as path signals just look at the lowest penalty, which might be a partly occupied platform, while with presignals you can force the train to go to an empty platform or wait at the entry for a free one.