1. British Standards Institute, 1983. B.S. 873—Road traffic signs and internally illuminated bollards. Part 6—Retroreflective signs.
2. Department of Transport, 1982. Damage to Low Bridges: Bridge Height Gauges. HMSO, London, UK.
3. Department of Transport, 1988. A Strategy for the Reduction of Bridge Bashing. HMSO, London, UK.
4. Department of Transport, 1991. Warning sign—indication of reduced headroom at hazard. (P)530.2—Specifications for drawings and markings. Department of Transport, London, UK.
5. Department of Transport, 1993. Progress to Reduce Bridge Bashing. HMSO, London, UK.