In 1995, Bill Brown spoke at an engineering conference in Gibraltar about a proposed bridge over the Strait of Gibraltar. It represented engineering challenges on a whole new scale, including another vast distance to span, strong winds, powerful currents, earthquakes and a very busy waterway. Nonetheless, he devoted much time to considering how such a bridge might be constructed.

In 1983, two years before he left Freeman Fox, Bill had presented initial suspension bridge designs for the Strait of Gibraltar to the governmental powers that be, focusing on ten spans measuring 2,000 metres each. He planned to position the bridge over the shallower seas of a subterranean ridge between Punta Paloma in Spain and Cap Malabata in Morocco. The total crossing would be 28 kilometres long. He would anchor the towers to the seabed using deep-sea oil-drilling platforms. A collapsible water-filled skirt would provide enough ballast to avoid and lessen the impact of ship collisions.

The new plans that Bill presented in Gibraltar in 1995 were based on work already carried out for the Messina Bridge. Once again, he used the concept of curved underbellies and box shaping to ensure smooth wind flow. Added stability came though the addition of perforated slots on the vented deck sections. This bridge still remains hypothetical; however the work Bill put into his designs helped clarify his research and moved international knowledge about suspension bridge design and innovation several crucial steps further forward.