When driving a high-decker touring coach or double-decker bus, why is precise route planning regarding bridge clearances and tree branches critical?

1. High-decker buses have low ground clearance and scrape on speed bumps
2. Double-decker buses are legally prohibited from reversing
3. The 4.0-metre vehicle height requires checking all overhead bridge clearances, underpasses, and tree canopies to prevent catastrophic roof impacts
4. Buses over 3.8 metres are exempt from all height restriction traffic signs