On-ramp signals were first introduced in Illinois in 1963 on Chicago's Eisenhower Expressway. Several other states – including California, Minnesota, Washington and Nevada – use them to effectively keep freeway traffic moving. They also are used extensively throughout Europe, most notably in England, France, Belgium, Germany and the Netherlands.
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2018-19 study the Institute for Transportation Research & Education at N.C. State University conducted in partnership with the N.C. Department of Transportation showed on-ramp signals positioned on Interstate 540 in Wake County to have various traffic benefits, including:
- 9 percent decrease in recurring congestion
- 12-minute decrease in duration of peak period
- Up to 2-minute decrease in drive time per day
The following table shows data from other U.S. cities that use on-ramp signals (data based on 2013 studies).