United States Department of Transportation
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Developing an area-wide system for coordinated ramp meter control.
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2008-12-01
[PDF-380.52 KB]
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Edition:Final report; Dec. 2008
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NTL Classification:NTL-INTELLIGENT TRANSPORTATION SYSTEMS-INTELLIGENT TRANSPORTATION SYSTEMS;NTL-INTELLIGENT TRANSPORTATION SYSTEMS-Freeway Management;NTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATION;NTL-OPERATIONS AND TRAFFIC CONTROLS-OPERATIONS AND TRAFFIC CONTROLS;
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Abstract:Ramp metering has been broadly accepted and deployed as an effective countermeasure
against both recurrent and non-recurrent congestion on freeways. However, many current ramp
metering algorithms tend to improve only freeway travels using local detectors’ inputs and
overlook the negative impacts on local streets. This may generate two problems: 1) the optimal
local settings may not result in a system-wide optimum in terms of traffic operations; and 2) the
increased congestion on local streets due to on-ramp overflow may counteract the gains in
freeway operations. To address these problems, we propose an area-wide ramp metering system
to improve the coordination of ramp meters for system-wide optimization and on-ramp overflow
minimization. Our experimental results show that our method can offer improved performance in
ramp metering operations under tested scenarios and also reduce the likelihood of on-ramp
overflow.
This novel strategy for active ramp metering is inspired by the principles of a computer
network congestion control strategy. In this strategy, certain types of congestion at a targeted
freeway location can be significantly reduced by limiting on-ramp vehicle flows to a fraction of
ramp demand and then additively increasing rates to avoid ramp queue spillover onto city streets.
This approach can be actively used to immediately curb the growth of traffic congestion and
therefore shorten travel delays. The effectiveness of this ramp metering approach has been
evaluated by microscopic simulation experiments. Our experimental results show that our
method can reduce system-wide travel delays in the tested scenarios by as much as 28.2% when
compared with the Fuzzy Logic ramp metering algorithm, and also reduce the frequency and
severity of on-ramp overflow. This indicates that this area-wide algorithm can provide benefit
when applied to urban freeway corridors for congestion mitigation.
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