What is the maximum permissible length of dimension X?

Your answer of 3 meters is correct. According to German traffic regulations, the maximum permissible width (dimension X) of a vehicle or its load, including any protrusions, is generally limited to 2.55 meters for passenger cars and 2.60 meters for refrigerated vehicles. However, for agricultural vehicles or trailers, a wider load is sometimes allowed—up to 3 meters in width if it does not endanger or obstruct other road users.

In this case, the image shows a trailer loaded with hay bales that extend beyond the sides of the trailer bed. The regulation allows a maximum width of 3 meters for such loads on agricultural vehicles. Exceeding this width would require special permits or markings to ensure safety on the road.

Understanding this rule is important for ensuring that loads are safely secured and not too wide for regular traffic, helping prevent accidents or obstructions.