Minnesota Department of Transportation

511 Travel Info

Ramp Meters

What they are, why we have them and what we've learned

A ramp meter.

Ramp Meters Nationwide

What other areas use ramp metering?

The largest ramp metering system in North America is located in Los Angeles County with more than 1000 meters. Since 1989, the number of meters nationwide has increased from about 1,600 to over 2,300. By the end of 1999, at least 33 metro areas had meters operating (source: Federal Highway Administration), including:

Metropolitan Areas with more than 50 meters Metropolitan Areas with
less than 50 meters
Chicago, IL
Los Angeles, CA
Minneapolis/St. Paul, MN
New York, NY
Orange County, CA
Phoenix, AZ
Portland, OR
San Diego, CA
San Jose/San Francisco, CA
Seattle, WA
Atlanta, GA
Columbus, OH
Denver, CO
Detroit, MI
Fresno, CA
Houston, TX
Milwaukee, WI
Northern Virginia, VA
Riverside, CA
Sacramento, CA
San Antonio, TX
San Bernardino, CA
Toronto, ON

How do these metering systems differ from one another?

There are two basic metering control strategies. One is "local control," in which a ramp meter operates based on conditions only on the ramp and the mainline point adjacent to the meter. Variations of this strategy are located in Chicago and Toronto.

The second strategy is "central control." Ramp meters and traffic detectors communicate with a central computer, typically located at a Traffic Management Center. The central computer processes the information and tries to coordinate timing among several ramp meters within a corridor. Several cities have centrally controlled systems including Seattle, Denver, San Diego and the Twin Cities. Each city, though, has its own strategies and goals for operation. Denver, Seattle, and the Twin Cities are examples of cities that incorporate information from queue detectors into the ramp meter timing.

MnDOT regulates meters based on a set of complex mathematical formulas. The formulas take into account various congestion level thresholds - including volume data (information on the numbers of vehicles actually traveling through the system). The more than 5,000 loop detectors (sensors) located in the pavement throughout the Metro area, collect the data. A computer at the Regional Transportation Management Center polls these sensors every 30 seconds. If there is sufficient traffic on the ramp and mainline, then the computer activates the meter. If there is very little traffic, the meter remains in a flashing yellow mode.

How effective is ramp metering?

Performance Measure Location and Result
Travel time Atlanta – 10% decrease in peak period
Houston – 22% decrease in peak period
Arlington – 10% decrease in peak period
Travel speed Milwaukee – 35% increase in peak period
Portland –155% increase in peak period
Detroit - 8% increase
Los Angeles – 15 miles per hour faster
Crash rate Phoenix – 16% decrease during metered hours
Milwaukee- 15% decrease in peak period
Crash frequency Portland –43% decrease
Sacramento – 50% decrease
Los Angeles – 20% decrease
Driver hours saved Sacramento – 50% decrease
Los Angeles – 8,470 hours per day
Vehicle volume Milwaukee – 22% increase in peak period
Sacramento – 5% increase in peak period
Detroit -14% increase in volume
Los Angeles – increase of 900 vehicles per day
Gallons of fuel saved Portland – 700 gallons per weekday
Emissions reduction Minneapolis - reduction of 1,160 tons annually
Benefit/Cost ratio Atlanta – about 4:1 in year 1, about 20:1 after five years