The Mackinac Bridge was built between 1954 and 1957 for $99.8 million, on time and within budget, and when completed it was the longest suspension bridge in the world if all three segments were counted. Designed to withstand crushing ice and winds of at least 632 mph, it safely carries 4.5 million vehicles each year and reflects the work of those who built and maintain it in the harsh winters and strong winds of the Straits. The bridge includes a truss bridge approach on each end and a central suspension section of three parts. Over the deep shipping channel, the suspension design allowed long spans, greater height, cheaper cost, and easier construction than truss bridges. Two massive anchor blocks stand at the edges of the deep water where the bridge changes from truss to suspension, with cables stretched between them across the chasm and supported by towers anchored into bedrock. The roadbed hangs from the cables, and the towers' height was calculated from the span and the desired clearance above the water. The roadbed is at least 148 feet above the water to allow freighters and tall sailing vessels to pass, and the cables drape over the towers through saddles rather than being hooked to them, allowing the cables and towers to move with weight loads and temperature changes.