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TEO / Divisions / Traffic Services / Ramp Signaling
Ramp Signals are traffic lights that have been working to reduce congestion along northbound and southbound Interstate 95 (I-95) in Miami-Dade County.
Ramp Signals are activated during times of heavy congestion, such as weekday rush-hour periods, but may also be activated in case a traffic incident or special event impacts regular expressway operations. The signals work based on real-time traffic conditions and alternate between red and green lights to control the rate which vehicles enter the highway. They break up the groups of merging vehicles to reduce the impacts of entering traffic to regulate the flow on the mainline. To date, Ramp signals have significantly improved mobility and travel speeds during the evening and morning rush hour periods by 16% and 11% respectively.
How Does Ramp Signaling Work?
Enforcement of Ramp Signaling is part of the 95 Express program. Drivers who fail to obey the traffic signals will be subject to penalties as permitted by law.
For more information on Ramp Signaling, click here.
Ramp signals are traffic signals installed on freeway on-ramps to control the frequency at which vehicles enter the flow of traffic on the freeway. As seen in the diagram below, vehicles traveling from an adjacent arterial onto the ramp form a queue behind the stop line. The vehicles are then individually released onto the mainline, often at a rate that is dependent on the mainline traffic volume and speed at that time. The configuration in the diagram is the most common; however, some agencies have altered this design to accommodate transit and high-occupancy vehicle (HOV) policies or existing geometric limitations.
Source: Parsons Brinckerhoff.
Without ramp signals in operation, multiple vehicles merge in tightly packed platoons, causing drivers on the mainline to slow down or even stop in order to allow vehicles to enter. The cascading slower speeds, both on the mainline and on the ramp, quickly lead to congestion and sometimes stop-and-go conditions. Ramp signals can break up the platoons by controlling the rate at which vehicles enter the mainline from the ramp, as shown in the figure to the right. This allows vehicles to merge smoothly onto the mainline and reduces the need for vehicles on the mainline to reduce speed.
In addition to breaking up platoons, ramp signals help manage entrance demand at a level that is near the capacity of the freeway, which prevents traffic flow breakdowns. Ramp signals are shown to reduce peak hour occupancies and quicken recovery from mainline breakdown back to or below the critical occupancy threshold. Typical results include reductions in travel time, reductions in crash rates, and increased traffic speed.
Ramp signals smooth the flow of traffic entering the freeway so vehicles can merge with mainline traffic with minimal disruption to traffic flow. Eliminating prolonged periods of stop-and-go conditions due to congestion can reduce vehicle emissions and fuel consumption on the freeway. It can be argued that emissions and fuel consumption increase at the ramp signal, which is why the environmental analysis must be sensitive to actual ramp operations and fuel estimation methodologies, especially with the prevalence of electric vehicles on the roadway.
Though it is typically difficult to measure, many regions have attributed reductions in carbon emissions and fuel consumption to ramp signaling implementation.
Florida Department of Transportation
Safety, Mobility, Reliability