RAMP METERS CASE STUDYPeter Langworthy, Kasia Winiarczyk, Kathy CarlsonA. BACKGROUNDGeneral BackgroundRamp Meters Background1B. RAMP METERS IN THE TWIN CITIESRamp meters: Twin Cities motorists have longest wait in nationRamp meters: Motorists approve of ramp meters but avoid themTwin Cities Ramp Meter EvaluationEvaluating Ramp Meters: Evidence from the Twin Cities Ramp Meter Shut-OffD. ADJUSTMENTS TO THE TWIN CITIES RAMP METER SYSTEM—ITS IMPROVMENTSBehind the Scenes at Mn/DOT’s Traffic Management CenterSenator Day and FREEDOM TO DRIVE pageTwin Cities Metro Area Ramp Meter Study Final ReportsOTHER STAR TIBUNE ARTICLESRamp meters: Meters change character of neighborhoodsRamp meters: Drivers get benefits, but many pay a priceEditorial: Ramp meters -- Shut-off shows transportation deficitRAMP METERS CASE STUDYPeter Langworthy, Kasia Winiarczyk, Kathy CarlsonA. BACKGROUNDGeneral BackgroundIn the 1950s and 1960s the federal government undertook a massive effort to build the interstate freeway system in the United States. While this system was envisioned primarily as to serve inter-state (hence the name) and inter-city traffic, it has come, over time, to be the backbone of intra-city transportation systems serving individual cities within the country. The overall interstate system was completed by the early 1970s and has not seen significant increases capacity since that time. However, the usage of the system, particularly in urban areas, has increased dramatically since that time. According the Federal Highway Administration (FHWA), during the last decade, metropolitan area traffic on the interstate system has increased by 30 percent, and FHWA projects that this increase will be 50 percent over the next ten years. The Twin Cities are no different from other US cities. In fact, our levels of increase in congestion in recent years are among the highest in the nation. Due to increased societal concern with environmental, social, and aesthetic impacts since the time of the initial construction of the freeway system, it is much more difficult and expensive to physically increase freeway capacity than it was to initially construct it. Thus, the problem which transportation professionals face is “how do we wring the most use possible out of the infrastructure which is in place?” One approach is to reduce demand for the over-extended capacity through efforts strategically restricting downtown parking supply, promoting car-pooling, telecommuting, and flex-time work scheduling (allowing non-peak commuting). This approach, referred generally to as Travel Demand Management (TDM), is a very important part of the effort. However, the focus of this case study is the converse perspective on the problem: Transportation Supply Management (TSM). TSM represents the approach of operationally managing the use of existing infrastructure as efficiently as possible so as to maximize the effective capacity of existing roadway systems. There are a broad range of TSM strategies which are available, including: signal coordination, reversible lanes, HOV lanes, an variable message signs (VMS). One of these strategies is the focus of this case study: ramp meters.Ramp Meters Background 1 Freeway ramp meters are traffic control signals which are installed at entrance ramps to freeway systems and are used to meter traffic onto the mainline at design rates. There are two primary functions which ramp meters serve:- to break up “platoons” of vehicles entering the freeway at given access points (thus allowing merging with less disruption to the mainline operations), and- to hold vehicles temporarily “in storage” on ramps to improve flow characteristics on the mainlines during peak travel times.Freeway ramp metering has been used as a control technology since the 1960s. The first comprehensive assessment, funded by the Federal Highway Administration (FHWA), was published in 1989. An updated version of this report was published in 1995. According to the 1995 report, the following Metropolitan areas had more than 50 ramp 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, WAIn addition, 13 other North American Cities used ramp meters (less than 50 meters per city in these cities). As of May 2000, there were no national standards regarding the installation and operation of ramp meters. Within the basic framework of the goals of ramp metering, transportation authorities can adopt operating policies somewhere within the following extreme cases:1. give highest priority to vehicles on the freeway (maximize mainline flow)2. give highest priority to vehicles on the ramp (minimize ramp queues) B. RAMP METERS IN THE TWIN CITIES The Twin Cities has the most aggressive ramp metering program in the country. It has over 425 meters throughout the metro area and, at least prior to testing done in 2000, these meters were operated under the first of the two “extreme” operating prioritiesidentified above—they focused upon maximizing flow on the mainline even at the expense of long queues on entrance ramps. Waits at ramp meters of five to ten minutes were common during peak hours on some facilities, and some waits were as long as 20 minutes. As congestion and ramp waits increased in the 1990s, public frustration with theramp metering system mounted. Refer to the following links:Ramp meters: Twin Cities motorists have longest wait in nationPublished Nov 28, 1999http://www.startribune.com/stories/781/36320.htmlRamp meters: Motorists approve of ramp meters but avoid themPublished Nov 28, 1999http://www.startribune.com/stories/784/40437.htmlC. 2000 TWIN CITIES RAMP METER STUDYTo address the frustration discussed in Section B, above, the Minnesota Legislature mandated that testing be done to assess the effectiveness of the ramp meters. This testing took place in fall of 2000, and was perhaps the single most comprehensive experiment in the history of surface transportation. Background travel data was gathered prior to the test, and then all ramp meters in the Twin Cities region were turned of for a period of eight weeks. Four interstate corridors were studied during this time, but motorists were not informed as to which corridors were being studied, because there was concern that this knowledge may affect traveler behavior. The very extensive
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