To recap the highlights of the 1.9 patch:
Brand new traffic car AI system;
Improved maneuverability, touches to suspension and collision physics (more work planned still);
Early support for Oculus Rift and gamepad-controlled mouse cursor;
Improved handling of automatic gearbox (more gears, interaction with cruise control);
Improved compatibility with semi-broken prefabs used in mods;
Improved error handling in radio playback.
Scania Streamline improvements (model, textures, paint jobs, new parts and accessories) - you may need visit truck dealer and re-purchase some parts;
Volvo FH16 improvements (interior, wipers, shadows);
Iveco Hi-way improvements (dashboard computer, shadows);
Paintjobs are properly applied on add-ons in interior views;
V8 engine sounds for Scania R and Scania Streamline.