Mini Motorways is a strategy simulation game about designing the road map for a growing city.
Better Motorways is an BepInEx Mod allowing modification of the core game.

Disclaimer:
This mod modifies game runtime, it might be seen as hacking.
Currently it seems there aren't any counter measurements for "hacking"

• Customise Simulation Rules
  • Vehicles
  • Lanes
  • Traffic Lights
  • Building Spawning
  • Suburb Spawning
  • Big Pins
  • Demand
• Toggle Vechicle collision

Install BepInEx for 32bit (x86)

The game is 32bit, this is why you need to install 32bit BepInEx.

Extract BepInEx to game folder.
Located in: ..\Steam\steamapps\common\Mini Motorways
Your folder should look something like:

|-- BepInEx
|-- Mini Motorways_Data
|-- doorstop_config
|-- Mini Motorways.exe
|-- winhttp.dll
...
...

Install this mod under Releases. Extract the folder from the installed .zip and move it under BepInEx\plugins\

Your plugins folder should look like

|-- BetterMotorways
  | -- BetterMotorways.dll

Run the game once and close it. This will create an config file under: BepInEx\config
Edit values under created config file and enjoy the mod.

Information on development here.