1900s	1910s	1920s	1930s	1940s	1950s	1960s	1970s	1980s	1990s	2000s

1951
Public Act 51 - the basic highway law in Michigan - passes which prohibits mingling general state funds with road receipts

1956
Congressional approval of a national interstate freeway system triggers the greatest highway building program in history

1955
World's first freeway-to-freeway interchange - at I-94 and M-10 in Detroit - allows motorists to make easy directional turns

1957
The five-mile-long Mackinac Bridge opens to traffic, linking Michigan's two peninsulas

1957
State Highway Department leases its first aircraft

1958
First "Welcome to Michigan" signs on major trunklines, also first "Gas-Food-Lodging" signs

1959
The Houghton-Hancock Bridge opens - a huge double-decker lift bridge with a four-lane highway on top and a railroad track below