Engineering changes the movement along roads from 2 to 3. Is there anyway of making other techs do this (from 3 to 4)? I have looked at the xml files for technologies and have found nothing, so i guess this uses python but unfortunately i dont know how this works. If someone could please tell me how to do this.

I think you're just looking in the wrong XML files :)

What you want is the <TechMovementChanges> element found in XML/Misc/CIV4RouteInfos.xml.

It's based on a product of 60. If movement rate listed is "20", movement is 3. 15=4, 10=6, etc.

You are looking for XML/Misc/Civ4RouteInfos.xml