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).
| Travel time | Atlanta – 10 percent decrease in peak period
Houston – 22 percent decrease in peak period
Arlington – 10 percent decrease in peak period |
| Travel speed | Milwaukee – 35 percent increase in peak period
Portland – 15 percent increase in peak period
Detroit – 8 percent increase |
| Crash rate | Phoenix – 16 percent decrease during metered hours
Milwaukee – 15 percent decrease in peak period |
| Crash frequency | Portland – 43 percent decrease
Sacramento – 50 percent decrease
Los Angeles – 20 percent decrease |
| Driver hours | Sacramento – 50 percent decrease |
| Vehicle volume | Milwaukee – 22 percent increase in peak period
Sacramento – 5 percent increase in peak period
Detroit – 14 percent increase in volume |
| Gallons of fuel saved | Portland – 700 gallons per weekday |
| Emissions reduction | Minneapolis – 1,160 tons annually |
| Benefit-cost ratio | Atlanta – benefits were four times greater than the cost after one year and 20 times greater after five years |