Up to what maximum overall width can vehicles transporting loose hay, straw, or fodder be loaded without a permit?

Answer: C — 3.7 metres

Vehicles transporting loose hay, straw, or fodder are typically bulky and large in size. Therefore, they require special permits for transportation to ensure road safety and proper weight distribution. Option A is incorrect because 2.5 metres is too narrow to accommodate large and bulky loads. Option B is incorrect because 3.0 metres is still considered narrow for such types of vehicles. Option D is incorrect because 4.2 metres is too wide for safe road transportation without a permit. The maximum overall width without a permit is 3.7 metres, which strikes a balance between ensuring road safety and allowing proper transportation of these types of loads.