Select environmental impacts: Minneapolis identified a net annual savings of 1, tons of emissions Note: emission values calculated based on a simplified approach on average changes in speed.
Other simulation analysis shows ramp metering to be effective in reducing CO emissions by 1, tons per year.
Mobility, Reliability, and Efficiency Ramp metering reduces mainline congestion and overall delay, while increasing mobility through the freeway network and traffic throughput. Travel times, even when considering time in queue on the ramp, are generally reduced when ramp metering is implemented.
Travel time reliability has become an important measure of ramp metering effectiveness. Many regions have experienced increased travel time reliability reduced variations in day-to-day travel times due to ramp metering.
Safety Ramp meters help break up platoons of vehicles that are entering the freeway and competing for the same limited gaps in traffic. By allowing for smooth merging maneuvers, collisions on the freeway can be avoided. Many regions have reported significant reductions in crash rates after starting ramp metering. Effective ramp queue management can prevent queues from spilling onto the adjacent arterial and clogging up the city street network with stopped vehicles that are waiting to enter the freeway.
Reduced Environmental Impacts Ramp meters 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 meter, which is why the environmental analysis must be sensitive to actual ramp operations and fuel estimation methodologies, especially with the prevalence of electric and hybrid vehicles on the roadway.
Though it is typically difficult to measure, many regions have attributed reductions in carbon emissions and fuel consumption to ramp metering implementation. The measured benefits of implementing ramp metering systems can outweigh the associated costs by a ratio of 15 to 1, as concluded in the Twin Cities Ramp Meter Evaluation. The cascading slower speeds, both on the mainline and on the ramp, quickly lead to congestion and sometimes stop-and-go conditions.
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 meters help manage entrance demand at a level that is near the capacity of the freeway, which prevents traffic flow breakdowns.
Ramp meters are shown to reduce peak hour lane occupancies i. Typical results include reductions in travel time, reductions in crash rates, and increased traffic speed. Through developed simulations and databases, agencies can model the effects of ramp metering on their existing freeway operations. These exercises can aid in the decision-making and planning process when planning for ramp metering deployment or expansion.
Several alternative strategies were considered, including geometric re-alignment of the interchanges. Ramp metering was selected over the alternative options because metering could be implemented more rapidly and at a fraction of the cost of other alternatives. WisDOT also wanted to use the deployment as a pilot test for analyzing the potential effectiveness of the strategy as a safety and congestion mitigation strategy. What was the process used to Locate Ramp Meters?
An earlier analysis of the incident management system deployed in the Madison region had identified the corridor as experiencing crashes at a rate exceeding the State average. Many of the local transportation professionals attributed the higher than expected crash rate to the congestion caused by difficult merges at several interchanges in the corridor.
The findings of this analysis were used to prioritize the implementation of the meters at the deployment locations. What have been the observed and perceived benefits of the deployment? Has the strategy achieved its goal of mitigating safety and congestion deficiencies? Two evaluation efforts have been subsequently conducted to assess the performance of the pilot ramp metering deployment. The first evaluation was conducted by University of Wisconsin transportation researchers using before and after field traffic traffic volumes, travel speeds, and travel time and crash data, microscopic traffic simulation analysis, stakeholder interviews, and public surveys.
The second evaluation was conducted by a transportation consulting company using a combination of the regional travel demand model and the U. Both evaluation efforts found that the ramp metering implementation provided significant benefits and was an effective strategy in reducing congestion and improving safety. Specific findings from the University of Wisconsin study [ 5 ] include: The number of crashes decreased significantly 50 percent reduction with ramp meters, particularly during the winter months.
Most agency personnel reported that the time to clear incidents improved with ramp meters. Ramp meters improved freeway mainline average speeds by two to ten percent.
Speed variability was reduced by 5. Ramp meters increased facility throughput by 29 percent. Ramp metering did not cause significant diversion of vehicles from Highway 12 to alternative routes. Most drivers obeyed the ramp meters with compliance rates averaging from 85 to 98 percent. Public surveys indicated that public acceptance of ramp meters was very high. Additional findings from the IDAS analysis include: The number of crashes was estimated to decline by 36 percent in the areas immediately upstream and downstream of the metered ramps.
Facility speeds were estimated to increase by three percent with ramp metering. Freeway mainline volumes were estimated to increase modestly 1. What resources were required to plan, deploy, and operate the system? As part of the evaluation, traffic data was analyzed that had been collected before September to May and after ramp meters were activated September to April In addition, researchers reviewed incident reports for crash data, conducted microscopic traffic simulation modeling, and conducted before and after opinion surveys of Dane County drivers.
A survey was also conducted of transportation and law enforcement agency personnel, including representatives of Wisconsin State Patrol — District 1, the Madison Police Department, Dane County , and Madison Metro Transit. The ramp metering evaluation was part of a larger study investigating ITS element costs and benefits. What specific challenges were encountered in planning and deploying the ramp meters? The most significant challenge in deploying the ramp meters was related to public acceptance.
Although many Madison residents were familiar with ramp metering through travel experiences in Milwaukee, Minneapolis, Chicago, and other nearby cities, many other regional travelers were unfamiliar with the concept. The deployment was accompanied by a public education campaign to explain the operation and purpose of ramp metering. Furthermore, public surveys were conducted both before and after implementation to gauge public acceptance and their understanding of the purpose of the ramp meters.
Positive driver perceptions on the effectiveness of ramp metering as a strategy for improving travel time and safety ranged from 32 to 64 percent of drivers prior to the implementation. The percentage of positive responses improved following deployment to a range of 78 to 92 percent of drivers. How has the effort evolved over time?
WisDOT is currently using the results from the evaluation efforts to assess the potential of ramp metering expansion in the region. Mainline metering involves installing traffic signals usually overhead on the mainline of a freeway. Some examples of freeway-to-freeway ramp metering in the United States, namely, in Minnesota and California, are examined and the advantages and disadvantages of freeway-to-freeway ramp metering are discussed.
The implementation and operational issues of the only known operating example of mainline metering in the western United States are also discussed.Freeway-to-freeway ramp metering involves installing traffic signals either on the side of the roadway or overhead on the ramps found at freeway-to-freeway interchanges. What was the process used to Locate Ramp Meters? The simulations can use new operational strategies like adaptive ramp metering coded directly into the software so that realistic environments can be evaluated for a proactive approach to congestion management. Ramp metering can also support regional congestion management processes. A majority of the freeway motorists 51 percent found the experiment to be good or very good. The suggested policy on mainline metering is to install mainline meters on freeways approaching bottleneck locations where analysis indicates that improved traffic operations would result.
Data regarding traffic volumes, travel times, and other appropriate performance measures should be collected, modeled, and analyzed both before and after ramp meters are installed.
This demonstration project showed how effectively the two agencies City and County of Honolulu and HDOT could work to meet the very demanding requirements and project schedule.
Geometric constraints also exist such as limited sight distance along a curved roadway and limited provisions to provide the required storage for queued vehicles on ramps. What parts of the planning process worked particularly well? Ten percent of freeway motorists rated the experiment bad or very bad.
An integrated database, that contains data such as roadway inventory, detector data, traffic counts, crash records, and incident records, can streamline the process to evaluate the effectiveness of various ramp metering strategies or algorithms. Were other ramp management strategies considered besides ramp closure? Given the positive performance of the ramp meters and the public acceptance, the expansion of the system to additional high priority interchanges and corridors is expected as funding becomes available. 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. It can be argued that emissions and fuel consumption increase at the ramp meter, which is why the environmental analysis must be sensitive to actual ramp operations and fuel estimation methodologies, especially with the prevalence of electric and hybrid vehicles on the roadway.
Of the motorists who use the Lunalilo Street on-ramp, 25 percent found the experiment to be good or very good, and 23 percent found it neutral. The cascading slower speeds, both on the mainline and on the ramp, quickly lead to congestion and sometimes stop-and-go conditions.