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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: FHWA-HRT-2006-005 Date: July/August 2006|
Publication Number: FHWA-HRT-2006-005
Issue No: Vol. 70 No. 1
Date: July/August 2006
A new FHWA handbook details the importance of managing freeway entrance and exit facilities for optimal mobility and safety.
|Poorly designed and managed freeway entrance ramps can have significant adverse mobility and safety impacts on nearby freeways and arterials.|
From rural towns to major metropolitan areas, traffic congestion is a growing problem throughout the United States. Lacking a silver bullet to fix the congestion problem, an increasingly important approach is to manage the roadway system more efficiently, maximizing the capacity of existing infrastructure.
State and local departments of transportation (DOTs) are turning to a comprehensive approach that uses multiple management strategies. One strategy is operating the transportation network proactively by using advanced technologies such as intelligent transportation systems (ITS) that can reduce congestion and improve safety. Many States also have successfully deployed other strategies such as improving incident management, traveler information, traffic surveillance and detection, and advanced traffic signals. However, one element of transportation infrastructure that tends to be overlooked is freeway ramps and ramp management strategies.
Freeway ramps serve an important purpose because they connect high-speed, limited-access freeways to one another and help to lower speeds on surface streets such as arterials and collectors. If designed, operated, and maintained effectively, ramps enable motorists to make connections between different facilities safely, conveniently, and comfortably, with little or no delay or impact on traffic conditions.
"Ramp management is one of the most powerful tools for managing freeway operations within an urban area," says Joel Marcuson, of Jacobs Engineering Group, Inc., and a member of the Transportation Research Board's (TRB) Freeway Operations Committee. "When asked which ITS element he would choose if allowed only one, an official from the Minnesota Department of Transportation [Mn/DOT] said 'ramp metering, without question.' A recent 'test' in the Twin Cities, where the ramp meters were turned off—and then turned back on after the public demanded it—seems to confirm that perception."
Today's traffic volumes and speeds on or near ramps often exceed the conditions for which the facilities were initially designed. In fact, ramps often are too closely spaced, do not offer adequate acceleration distances for posted speeds, or are simply overwhelmed by the increasing number of motorists who use them. These conditions can affect the efficient and safe movement of traffic on the ramps themselves and on the highways and arterials to which they are connected.
A new Federal Highway Administration (FHWA) publication, the Ramp Management and Control Handbook, compiles best practices from around the country to help traffic managers and roadway designers maximize the effectiveness of their on- and off-ramps. The handbook is a companion to FHWA's Freeway Management and Operations Handbook (FHWA-OP-04-003).
In recent decades, a number of researchers have developed approaches to improve ramp operations and safety. Traffic managers in Chicago, IL, Detroit, MI, and Los Angeles, CA, implemented ramp metering at selected sites as early as the 1960s. But no single resource documented the lessons learned, recommended practices, measured benefits, or discussed key considerations in ramp management. To fill this knowledge gap, FHWA initiated a project in 2003 to develop a comprehensive handbook on effective ramp operations.
|The Ramp Management and Control Handbook, the cover of which is shown here, continues FHWA's efforts to provide comprehensive, easy-to-use resources on roadway management.|
The intended audience for the new handbook includes transportation professionals involved in planning, designing, monitoring, operating, and evaluating the performance of traffic management at freeway ramps. Specifically, the document targets managers of traffic management centers (TMCs), decisionmakers, engineers, planners, operations staff, and roadway designers. The intent of the handbook is to improve traffic safety, traveler mobility, and travel time reliability on ramps and their neighboring freeways and surface streets while reducing environmental impacts, such as tailpipe emissions, caused by vehicular travel and delay on those facilities.
|Ramp management should be viewed as one piece of an overall, integrated effort to successfully manage the surface transportation system (signified by the smaller puzzle). This figure of a jigsaw puzzle illustrates that ramp management is typically considered one integrated piece of freeway management, while freeway management in turn is an integrated piece of the overall surface transportation program.|
The Ramp Management and Control Handbook addresses several key topics associated with planning, implementing, operating, and maintaining on- and off-ramps. Topics include the following:
The handbook is organized into 11 chapters, which sequentially follow the process of planning, designing, operating, and maintaining ramps.
|Ramp metering signals, such as those shown here, have proven to be a highly successful and beneficial strategy across the country. Note that the red color of the legends on the blank-out signs in this photo does not comply with the 2003 edition of the Manual on Uniform Traffic Control Devices (MUTCD).|
The handbook defines ramp management as the application of control devices, such as traffic signals, signing, and gates, to regulate the number of vehicles entering or leaving a freeway and to achieve operational objectives. Most strategies for managing ramps are employed to balance freeway demand and capacity, maintain optimum freeway operation, improve safety on the freeway or adjacent arterials, or give special treatment to a class of vehicles, such as high-occupancy vehicles (HOVs).
These strategies and the equipment and systems that support them often are used in conjunction with other freeway management programs to create operational efficiencies and help meet overall transportation management goals. The relationship between ramp management strategies and other management programs can be likened to puzzle pieces with ramp management and the other programs representing the pieces that need to come together to ensure successful operations. In addition to freeway management, ramp management should be coordinated closely with arterial management, transit management, and other parts of the overall surface transportation system.
The handbook lists four proven and accepted strategies to manage traffic on ramps. The first is ramp metering, which utilizes traffic signals at entrance ramps to control the rate at which vehicles enter freeways, thus smoothing traffic flow. Traffic managers can program ramp meters to release vehicles one at a time or in small (usually two-vehicle) platoons to mitigate the impact of heavy volumeon freeway traffic flow. One ramp meter may be coordinated with others to smooth the traffic flow at a chosen point along a stretch of freeway or to smooth the flow on several freeways within a regional network. In addition to optimizing freeway flow, programming ramp meters can reduce some of the adverse impacts of congestion, such as collisions, delays, vehicle tailpipe emissions, and fuel consumption.
Minnesota has seen considerable success with ramp metering, according to Eil Kwon, traffic research director in Mn/DOT's Office of Traffic Safety and Operations. A 2001 meter shutdown study found that the lack of metering resulted in "decreases of 9 percent in freeway volume, 14 percent in travel speeds, and 91 percent in travel time reliability, with increases of 22 percent for travel time and 24 percent for crashes," he says. "The main challenge in metering is how to maintain certain levels of queue at on-ramps to achieve systemwide efficiency, while simultaneously addressing drivers' desires not to wait long."
Many transportation professionals consider metering to be the most beneficial of the ramp management strategies. "Our region first installed ramp metering in [Washington] State's largest urban area in the early 1980s, and we have steadily expanded the system since then," says Pete Briglia, a principal transportation planner for the Puget Sound Regional Council and chairman of TRB's Freeway Operations Committee. "Other, smaller cities in our State have seen the benefits and are planning ramp meter systems. Every evaluation of the system has shown reduced [crashes], reduced delay, and increased volumes when metering was installed. No other traffic management strategy has shown the consistently high level of benefits in such a wide range of deployments from all parts of the country."
Ramp closure is another proven strategy, this one involving the use of gates, barriers, or other physical means to restrict vehicle access to entrance or exit ramps. In most cases, ramp managers consider closure for its safety benefits, such as at locations with severe geometric limitations, but this strategy also is effective for managing traffic during special events or controlling traffic in or around work zones.
Depending on conditions, ramps may be closed to all traffic or to specific vehicle classes on a temporary, intermittent, or permanent basis. For instance, a ramp near a work zone with a high percentage of large construction vehicles may be closed to all nonconstruction-related traffic.
Ramp closures change established traffic patterns and therefore should be considered only for rare situations where other management approaches are deemed inappropriate to achieve the desired results. Also, before making the decision to close a ramp, traffic managers need to reroute the traffic that normally uses the ramp. Rerouting entails developing detours and conducting a public information and outreach campaign to alert motorists about the closure and alternative routes.
A third management strategy is special use treatment, defined as preferential treatment for a specific class or classes of vehicles at exit and entrance ramps. Preferential treatments include special lanes on ramps for exclusive use by HOV motorists. This strategy often requires regional support for funding and deployment, therefore interagency and intermodal coordination and cooperation are essential. For example, transit management programs might identify ramps where transit vehicles are given priority.
Finally, ramp terminal treatments are a strategy that managers can deploy to improve localized problems at entrance and exit ramp terminals ("terminal" defined as the connection point of the ramp with either the intersecting arterial or the freeway facility). Signal timing, ramp widening, turn lanes, additional queue storage for stopped vehicles on arterials, signing, pavement markings, and other features focus on solving problems at the intersection of the ramp and arterial. At exit ramp terminals, these strategies can help reduce queues that spill back onto the freeway, or they may enhance arterial flow by limiting the freeway traffic that can access certain streets in the network. At entrance ramps, terminal treatments can improve coordination between ramp meters and traffic signals, address insufficient storage space on the ramp, and notify or guide drivers.
Ramp management strategies produce benefits in many areas:
Safety—Ramp management improves the flow and mix of vehicles that enter and exit freeways, reducing disruptions that can lead to collisions. Ramp metering is particularly effective at breaking up large platoons of vehicles, thereby smoothing traffic flow. In Denver, CO, metering helped cut freeway crashes in half, according to a 1995 FHWA study, Ramp Metering Status in North America (DOT-T-95-17).
Mobility and Reliability—Ramp management can reduce congestion, which in turn increases travel speeds and reduces travel times. The 1995 FHWA study of ramp metering in North America found that implementing ramp management strategies in Detroit increased average speeds and volumes by 8 and 14 percent, respectively.
Environmental Benefits—FHWA studies have shown that ramp management, by reducing congestion and delay, also decreases the total vehicle pollutants released into the environment. In Minneapolis, MN, ramp metering reduced overall emissions by 1,052 metric tons (1,160 tons) annually, according to the study Twin Cities Ramp Meter Evaluation: Executive Summary, sponsored by Mn/DOT in 2001.
Institutional Efficiency—In addition to the tactical benefits, ramp management also promotes institutional cooperation by serving as a conduit through which agencies can collaborate to address transportation needs. Because ramps often join facilities operated by multiple agencies, ramp management can break down barriers that exist between the agencies, enabling them to work together more effectively on other issues as well.
|Ramp management strategies can help alleviate traffic disruptions and crashes, such as the one shown here.|
Despite the benefits noted above, ramp management strategies that are not properly planned and implemented can cause more harm than good. For example, strategies may unintentionally shift problems from one location to another; create unnecessary queue spillback, such as when a ramp meter causes queues to back up onto adjacent arterials; produce equity concerns, such as when a ramp closure adversely affects local businesses; or attract public opposition due to misconceptions about the proposed strategies. To ensure successful deployments, the handbook instructs traffic managers to use care in selecting strategies.
|Carefully selecting the proper ramp management strategy is crucial to achieving safe, orderly traffic flow on and off roadways, such as shown here.|
Although there are only four main classifications of ramp management strategies, each encompasses a variety of approaches that can address specific needs. Narrowing the list of potential strategies before beginning a detailed analysis of each is important for saving time and costs.
The handbook outlines a four-step process for systematically selecting the best strategies:
Step 1: Revisit Agency Policies, Goals, and Objectives. Ramp management strategies should align with an agency or region's transportation policies and objectives. Further clarification and understanding of these goals will help identify the strategies that best fit within a transportation management program.
Step 2: Evaluate Baseline Conditions. Evaluate current- or future-year baseline conditions first to determine whether the existing problems are crucial. Just because a ramp management strategy is feasible and fits into an agency's transportation management program does not necessarily make it appropriate to implement. A thorough evaluation of the baseline conditions could reveal that a ramp management strategy is not warranted.
Step 3: Match Needs With Identified Strategies. The next step is to match the needs or problems identified in step 2 with the conditions that ramp management strategies are known to help mitigate. If the needs align with conditions, then specific strategies should be analyzed in detail to determine their suitability.
Step 4: Select and Analyze Appropriate Strategies. If road managers successfully map ramp management strategies to existing needs, then the next step is to determine whether the anticipated benefits outweigh any negative impacts and ultimately decide whether the strategies should be implemented.
Before purchasing systems or equipment, traffic managers need to coordinate internally with upper management to determine the strategy's feasibility. Issues to consider include scrutinizing the minimum requirements necessary to deploy and operate the chosen management strategy successfully, such as staffing levels and training, hardware and software, budgetary resources and constraints, and policy directives.
As noted earlier, the implementation of ramp management strategies often requires coordination between various agencies to establish regionwide policies for resolving associated issues. Coordination needs to continue beyond the planning and into the operations stage. Several types of agencies with differing agendas will likely be involved with or affected by ramp management strategies, including law enforcement agencies; the traffic engineering and operations departments of local, city, or county agencies; and local transit agencies. Therefore, the handbook recommends that traffic managers draft new or revise existing policies to ensure equity among motorists and agencies across jurisdictional borders.
Public understanding and support are critical to ensuring success in meeting the goals of a ramp management initiative. Opposition to a strategy may significantly delay or obviate implementation. Therefore, soliciting support from the public, affected agencies, and internal stakeholders is important. Information campaigns also garner public input, which is valuable for evaluating and selecting ramp management locations and strategies. The input also is helpful for establishing program goals.
Outreach should target local leaders, motorists, the media, and external agencies thought to affect, or be affected by, the selection of strategies. Whenever possible, outreach efforts should be tailored to the concerns of each group affected by the strategy. Likewise, the reasons for and benefits of ramp management approaches need to be expressed in terms that each group can easily understand.
|Ramps are a critical link in the transportation system, and applying ramp-appropriate management strategies can help nearby freeways and arterials operate smoothly and safely.|
As the volume of road users in the United States continues to grow, transportation agencies are realizing the importance of operating roadways to maximize their existing capacity. Ramp management is an important tool that managers can use to regulate the overall transportation system. The management strategies of ramp metering, ramp closure, special use treatment, and ramp terminal treatment are known to improve mobility, travel time reliability, and safety with regard to ramps and roadways.
In a single resource, FHWA's Ramp Management and Control Handbook documents the latest guidance, measured benefits, lessons learned, best practices, and key considerations. "With this tool, traffic managers have the technical information they need to make the right decisions to keep their freeway ramps and the roadways they serve operating smoothly and safely," says Jeffrey Lindley, former director of the FHWA Office of Transportation Management and now the associate administrator for the Office of Safety.
James Colyar is a highway research engineer in the FHWA Office of Operations Research and Development at the Turner-Fairbank Highway Research Center in McLean, VA. He has been with FHWA for 5 years and manages various research projects on traffic operations. He holds a bachelor of science degree in civil engineering from the University of Idaho and a master's in civil engineering from North Carolina State University.
Jason J. Stribiak is a transportation systems planner with PB Farradyne. In his 5 years with the company, he has worked extensively on planning, operations, and research-related projects tied to ITS. He holds a bachelor of science degree in community and regional planning and a master's in transportation from Iowa State University.
Les Jacobson is the western systems manager for PB Farradyne. He is involved with or manages ITS projects across the country and has been involved in many aspects of freeway management as well. Previously Jacobson was the assistant regional administrator for traffic systems at the Washington State Department of Transportation, where he worked for more than 20 years.
Lisa Y. Nelson is a lead ITS engineer with PB Farradyne. She has more than 9 years of experience in ITS, traffic engineering, and transportation planning in both the private and public sectors. She holds a bachelor's in civil engineering from the University of Washington and is a licensed professional engineer in Oregon.
To download a free copy of the handbook, visit the FHWA "Freeway Management Program" Web site: http://ops.fhwa.dot.gov/freewaymgmt/index.htm.