Ramp Metering: A Proven, Cost-Effective Operational Strategy—A Primer

3. Keys for Successful Ramp Metering Deployment or Expansion

Whether an agency is expanding its already robust system or deploying ramp meters for the first time, there are key components of the planning and implementation process that it should keep in mind.

Figure 9: Ramp metering deployment decision process flow

Source: Parsons Brinckerhoff.

3.1 Is Ramp Metering Right for You?

The agency attempting to start new projects or deploy new systems should have an understanding of the high-level regional and agency goals, both short-term and long-term. New projects, including ramp metering deployment, should contribute to and complement existing initiatives and adhere to high-level objectives.

Ramp metering should be deployed with purpose to address existing operational issues (Figure 9). The primary issue ramp metering can mitigate is recurring mainline congestion; however, the agency may also want to increase safety at merge points and on the mainline and control mainline access during construction activities, special events, or traffic incidents. All of these issues have the potential to be aided through ramp metering and are valid reasons to pursue this strategy. However, if these issues are not present in the region or corridor, ramp metering is not an applicable strategy and should not be pursued.

Once the agency determines that its issues are relevant to ramp metering, it must determine if ramp metering is a feasible strategy to pursue. It can conduct feasibility studies to allocate resources efficiently and determine where ramp meters would be effective. Through evaluating outcomes from feasibility studies, it can discern whether or not a ramp meter is warranted at a particular location and get a preliminary glimpse into the potential effectiveness and magnitude of benefits.

Benefit/cost analysis is an additional tool that assigns a dollar value to the expected costs and benefits of ramp metering, which can determine and communicate the value of the project. Because the agency may face operations, maintenance, and capital costs as barriers, a benefit/cost analysis that yields a high ratio or positive net present value will provide leverage when seeking or appropriating funds. This type of analysis can be applied to a variety of constraints and scenarios, making it scalable to numerous regions that want to investigate ramp metering. Furthermore, this technique can be used for initial deployment and to measure the incremental benefit of expanding or improving a ramp metering system for ongoing performance reporting.

The agency should also assess its organizational capabilities and evaluate whether it is mature enough to undertake ramp metering deployment. Ramp metering deployment requires the operating agency to perform a multitude of tasks. Agency assessment can often identify strengths and areas that need strengthening. Agency assessment will prioritize areas of improvement by evaluating the internal capability to successfully implement ramp metering according to various organizational dimensions. The TSM&O capability maturity model is an assessment tool that identifies six dimensions of capability in which the agency can determine its level of maturity.

If the results from these various exercises indicate ramp metering is both appropriate and feasible, then the agency should take the next step in moving toward ramp metering deployment, which includes making sure that ramp metering projects are in the agency transportation plan and program.

3.2 Getting Ready for Ramp Metering

A systems engineering approach should be taken on all ramp metering projects, as required by FHWA Final Rule 23 CFR 940 for federally funded ITS projects to conform to the National ITS Architecture and standards. Going through the systems engineering process in the project development stage can guide the agency through the procurement, construction, fabrication, and systems acceptance phases of a project. An agency can tailor and scale the “V” systems engineering model, the FHWA preferred model for ITS projects, to fit the complexity of a project. One of the primary benefits in following these processes is early stakeholder involvement, the coordination with regional ITS architectures, and identification of interface points. Although systems engineering may require more effort at the beginning than would be conducted otherwise, the end result is a ramp metering system that is highly functional, efficient, has a reduced risk of failure, and one that can evolve with a minimum level of redesign and cost.

To define project costs and a timeline, the agency should identify staffing and training needs and create specific procedures for testing, installing, and maintaining software systems and field devices if these procedures are not already established through previous ramp metering deployments. These procedures are key concepts in the systems engineering process.

Traffic data collection prior to and after ramp meter installation measures the benefits of the implemented ramp metering strategies. A consistent approach to collecting, modeling, and analyzing traffic volumes, travel times, and other performance measures should be established early in the project development process.

Agencies, such as FDOT, are finding success with established procedures to guide management through the ramp metering implementation process.

Gain public and agency support

Because negative perceptions held by the public and other local agencies can hinder ramp metering deployment or expansion, the agency should devote efforts to outreach and collaboration.

To familiarize the public with ramp metering and to encourage their support, the agency should conduct outreach that proactively disseminates information to the public and clearly communicates the benefits of ramp metering. These efforts may include gathering public feedback, answering questions from the public, conducting focus groups and open houses, and issuing statements to local media. In order to reach a broader local population, the agency should maintain FAQs and other important information on a website and distribute this information via brochure or flyer. Providing clear information and addressing questions adds transparency to the planning process, which the public will generally favor. The agency could address stakeholder misconceptions of actual or perceived operations and maintenance costs by a thorough evaluation of costs associated with operating and maintaining ramp metering systems.

Local officials and interest groups can be instrumental in gaining widespread support. The agency should reach out to local officials to communicate the benefits of ramp metering and collaborate to address potential and existing issues.

Inter-agency cooperation is essential for early and on-going coordination. Inter-agency support can be won by assembling and providing supporting information that justifies the need for ramp meter deployment or expansion. The agency can develop agreements among each other to address known concerns, which can be a mutually beneficial relationship. For instance, a key element of successfully ramp metering is driver compliance. Transportation agencies should work with enforcement agencies to develop a cohesive enforcement plan.

Identify costs and funding sources

The agency can utilize FHWA tools, such as the USDOT Knowledge Resources website, to identify capital costs related to the installation of new systems. FHWA tools can also be used to identify and estimate corresponding benefits to be used in funding and programming decisions. The agency can strengthen its case for deploying ramp metering by itemizing specific costs, thus increasing transparency.

Providing benefit and cost information can help strengthen the case for ramp meter expansion by showcasing the benefits and providing leverage for requesting funds.

In order to secure funding, the agency must communicate the high priority of ramp metering to authorities. In agency budgeting processes, provisions for ramp meter installation should be included in future construction planning efforts.

Understand traffic conditions and volumes on ramps, mainline, and arterials

Successful ramp metering requires an understanding not only of the ramp conditions but also the conditions and volumes of the mainline and surrounding arterials. Thus, the agency should monitor the ramp, mainline, and arterial conditions to inform ramp metering policies, procedures, and strategies.

When evaluating mainline conditions, the agency should identify segments of freeway that show congestion forming near particular ramp locations. Metering these ramps can balance mainline volumes within the segment and reduce overall congestion. The impact of queue spillover on the local road network is potentially disruptive for arterial traffic flow and poses problematic merging and turning situations. The agency should collaborate with the arterial signals operators to enhance safety and effectiveness of ramp meters through signal timing, arterial striping, and ramp metering rates to manage queue backup.

Consider queue lengths and delay

Upon observation of system-wide traffic conditions, and the collection and analysis of traffic volumes at each ramp, an agency can determine whether or not they need to implement queue management strategies at single or multiple ramp locations.

The queue length on the ramp will be impacted by both the mainline and arterial traffic conditions. While queue management is a key consideration for optimizing freeway operations, the amount of time spent in a ramp meter queue generally adds to negative public perception. Queue management is closely related to the geometric limitations of the existing ramps, so both should be considered when exploring options. Two approaches to address queue length are increasing queue storage through lengthening the ramp or widening the ramp through adding pavements or restriping, or reducing the queue length through the techniques mentioned below.

Ramp metering technology has developed various methods of queue detection and corresponding solutions handled either by being hard-wired into the controller or with the software as a function of the control algorithm. It is important to deploy a system that provides operators with information about the length of queue wait times. If adding additional storage capacity at a ramp is not feasible, the agency could consider adjusting the metering control scheme to increase ramp metering capacity.

Strategies to increase ramp metering capacity include dual-lane or dual-release metering, implementing the use of the ramp shoulder as a metered lane during peak periods or restriping the shoulder lane to allow for an optimal acceleration lane taper (see Figure 10 for a typical sign). These are lower-cost options for controlling the queue.

Because queue length is a crucial aspect of ramp metering operations that is relevant to many stakeholders, the agency should create policies on maximum queue wait time and be able to communicate and justify these policies publicly.

Figure 10: Typical sign used to convert single lane on-ramp into dual-lane queue storage or allow conditional use of the shoulder

Source: Parsons Brinckerhoff.

3.3 Operating Ramp Metering Effectively

Monitor performance

After deploying or expanding a ramp metering system, the agency should assess various dimensions of the system’s performance. It should establish which metrics to measure, appropriate benchmarks for those measures, and monitoring and reporting procedures.

Performance monitoring can be used to identify areas of improvement and make small tweaks to the algorithm and overall system after the initial ramp metering deployment. Performance monitoring can also aid the agency in building inter-agency and public support for ramp metering. Creating public relations materials or reaching out to media regarding performance can increase the favorability of ramp metering with citizens, local businesses, and local governments. Providing agency transparency on the effect ramp meters are having on the freeway network is a successful strategy to overcoming opposition and determining target areas for improvement.

Figure 11: Dimensions of performance monitoring

Source: Parsons Brinckerhoff.

Analyze costs and benefits

Measuring the costs and benefits of a proposed ramp metering system is a practiced strategy for accelerating ramp metering deployment. The agency could face scrutiny regarding the proposed benefits of ramp metering in its region. A benefit/cost analysis can make the case for ramp metering more convincing. FHWA has developed resources to assist in this analysis. The Intelligent Transportation Systems (ITS) Benefits database documents findings from evaluations of a variety of ITS deployments on system performance, categorizes benefits by ITS goal areas (such as customer satisfaction, mobility, safety), and provides a comprehensive summary of benefits that can help the agency in making informed planning and investment decisions. A companion to the Benefits database is the Costs database, a national resource of costs estimates for ITS deployments. The Tool for Operations Benefit/Cost (TOPS‑BC) spreadsheet is designed to assist agencies in conducting benefit/cost analysis and to provide additional structure to critical decision-support actions and analysis of selected key TSM&O strategies. Another useful resource for analyzing impacts from ATDM strategies is the recent update to Chapter 35 of the Highway Capacity Manual (HCM), which describes methods to analyze freeway mainline effects of ATDM strategies, such as ramp metering.

There are numerous costs associated with ramp metering, including capital and maintenance costs associated with hardware and installation, user costs, and other costs stemming from congestion, environmental pollutants, and safety. A sound evaluation of the benefits and associated costs of ramp metering can make a compelling case to relevant stakeholders that ramp metering would benefit a given area.

Monitor and manage ramp queues

Following the activation of ramp meters, the agency should give particular attention to the length and behavior of the ramp queues. As discussed, excessive ramp queues that back up onto arterials are hazardous from both an operational and public relations standpoint. A common criticism of ramp metering from the public is the time drivers must spend in queues, so maintaining support for ramp metering can be contingent on managing queues. In addition, drivers are more likely to comply with ramp meters when the queue is reasonable. The agency should establish policies and methods for regularly monitoring the ramp queues, as traffic conditions can change over time and throughout the day.

Through its data collection and analysis processes, the agency should make adjustments to algorithm parameters as needed. To accommodate various ramp dimensions, it may change the configuration of the ramp. This could include forming two-lanes during metering, lengthening the storage lane, and adding a full-time lane. The release policy could also be increased to two cars per green, which would allow cars into the mainline at a higher rate.

Figure 12 distills the keys presented above into mitigation strategies for common barriers to ramp metering.

Figure 12: Ramp metering deployment challenges and mitigation strategies

Source: Parsons Brinckerhoff.