The maximum allowable height of a vehicle on a highway is:

Answer: B — 4.15 metres (13.6 ft)

The maximum allowable height of a vehicle on a highway is 4.15 metres (13.6 ft). This is because most bridges and overpasses on highways are designed with a clearance of around 4.3 - 4.5 metres (14 - 15 ft), so any vehicle taller than that may not fit through or could potentially cause damage. Option A (4.50 metres) and D (5.00 metres) are both higher than the typical clearance of bridges and overpasses, making them incorrect choices. Option C (3.75 metres) is smaller than the acceptable minimum clearance, which could also cause problems for taller vehicles. Therefore, option B (4.15 metres) is the most accurate and safe choice for the maximum allowable height of a vehicle on a highway.