In Canada the Standard Takeoff 'VIS' is 1/2 mile..
Most Carriers have 'operational Specifications'(Due to training)of Takeoff visabilities of 1200'(or 600' depending on the runway facilities-centre line lighting etc)..The main difference between 2/engine aircraft and 3/4 engine types is that the Takeoff diversion Alternate Airport is 'closer'(one hour engine out cruise)..This in itself is only a Carrier'requirement,and these days this requirement is questionable with the Engine out Category3 capabilities of the fleets....EG:should the field requirements(lighting etc)operate one could return with an engineout autoland....
