2.5 meter for road approval at 40km/h  ( 8 feet 4"   25 mph)
3.5 meter for  25 km/h  (11feet 8 " , 16 mph) with special lights
4.5 meter (15 feet) with an accompanying car in front of the tractor with ag convoy signs and lights on both car and tractor

and  a lot of small cities now have  some road narrowing in their entrance for slowing car flow (3 to 3.5 metre wide)  (see this: http://www.securite-routiere.org/infrastructure/chicanes/c3mareilg.htm)

and weight limit is 19 metric tons (42200 pounds) for a 4 wheel vehicle

so it is not easy to have a big ag machinery approved here

big combines more than 19 metric tons appear now with tracks or tird axle for west european market