Are you using any mods that affect traffic and public transport in any way? Or does this happen in a completely unmodded game?
We'll need to have a look at your log then, which unfortunately means I'll need you to make a post on our support forum as Steam doesn't let you attach files here. You can attach it directly when making a post on the support forum here:
https://forum.paradoxplaza.com/forum/forums/support-bug-reports.879/
We need the output_log.txt which can be found in the Cities_Data folder where the game is installed, usually something like this: C:\Program Files (x86)\Steam\steamapps\common\Cities_Skylines\Cities_Data
You can also find the folder by right-clicking on the game in your Library, select Manage and then Browse Local Files. Then just go into the Cities_Data folder and find the output_log.txt