Factorio Forums

Diagonal rails are shorter than rectilinear ones, resulting in diagonal rail lines costing more per kilometer. This goes against the intuition that rails are the same regardless of their orientation. The horizontal/vertical rails need to be about 30% shorter, or diagonals need to be about 40% longer, for parity.

Here are 100 diagonal rails and 100 horizontal rails for comparison. You can see that the diagonal tracks are shorter than the horizontal tracks (it helps to use a ruler). With this behavior, you need about 140 diagonal rails to equal the length of 100 horizontal rails.
There was a previous discussion of train cars changing size depending on their orientation (viewtopic.php?f=5&t=17795), however, I haven't seen any report of rails changing size.

Not a bug.

Since diagonal rails have length of 1.41 per entity and they cost 1 rail while horizontal/vertical straight rails have lenght of 2 per entity and they cost 1 rail and since we have no fractional entity costs or fractional item counts in inventory, it is just not a bug. Going by the proposed logic, building curved rails is also not optimal since they have length of 7.84 (viewtopic.php?p=594090#p594090) while costing 4 items. There will be a lot more cases in 2.0 where cost to build is not proportional to the length provided.