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Ramp Meters in the USA
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Gabriel Côté

Jan 23, 2024

Ramp meters are more and more present in urban areas, but how do they work? Are they effective? This article shows their benefits and their problems.

Ramp meters have become more and more present on the highways of the United States and are a new method to reduce traffic jams: “ramp meters are traffic signals installed on freeway on-ramps to control the frequency at which vehicles enter the flow of traffic on the freeway.”

How Does It Work?

Ramp meters are barely different from the usual traffic signals. They are composed of two signal lights: green and red. Drivers pull up to the white line at the on-ramp, which is the entrance of the highway. When the signal turns green, one car can cross the line. 

Ramp meters are equipped with computers to calculate and control the traffic flow. Computers can control traffic either with a local or central system. Locally controlled ramp meters are set based on live trends of the specific location or based on local conditions, such as rush hour periods. Central controlled ramp meters are responsive to system-wide conditions. Traffic detectors and ramp meters send information to a central computer, which processes the information from all ramp meters of the region to coordinate timing among all ramp meters.

Benefits

A study from the U.S. Department of Transportation counted four fundamental benefits: efficient traffic, safety on highways, reduced environmental impact and an overall positive benefits/cost ratio.

First, ramp meters help highways become more efficient. They increase traffic speed while reducing mainline congestion in many cities. Portland (Oregon) recorded the best results: the average traffic speed of the city increased by 160% while the travel time was reduced by approximately 145%.

Second, the number of collisions and injuries from accidents on highways decreased in many regions that installed ramp meters. Automobilists have more time and space to merge on highways, which reduces the risks of collisions.

Third, ramp meters can eliminate long periods of stop-and-go traffic circulations, which reduce “vehicle emissions and fuel consumption” on highways.

Lastly, the benefit/cost ratio is positive. The benefits gained from ramp meters, including time and gas expenses, win over the cost, such as the amount spent to install these ramps, to a ratio of 15 to 1.

Problems

The main problem is equipping existing highways with ramp meters. Many on-ramps need to be remodeled because they are simply too narrow for an adequate acceleration length with enough space to hold long queues.

The second problem is funding. Agency for freeway operations that want funding from local, state or federal government to install ramp meters compete with other projects that may have priority over them, such as bridge repairs. If this is the case, it can also lead to a lack of agency support. Local agencies may also perceive that ramp meters will have negative consequences on their transportation system.

The last problem is the public opposition. The public sometimes doubts the efficiency of ramp meters and sometimes have misconceptions about them, such as the perception they favor people “who live outside city centers.”

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