<Li> Total length of wire in main cables: 42,000 miles (68,000 km). </Li> <Li> Total vehicle crossings, 2005: 4,236,491 (average 11,608 per day) </Li> <Li> Speed limit: 45 miles per hour (72 km / h) for passenger cars, 20 miles per hour (32 km / h) for heavy trucks . Heavy trucks are also required to leave 500 feet (150 m) spacing ahead . </Li> <P> Five workers died during the construction of the bridge . </P>

What is the speed limit on the mackinaw bridge