Office of Operations
21st Century Operations Using 21st Century Technologies

Synthesis of Active Traffic Management Experiences in Europe and the United States

4.0 System Level Applications

This chapter examines benefits at the corridor and system level, reporting on identified or potential synergistic relationships between any of the European- or US-based traffic management techniques. System level applications will examine the following contextual settings:

  • Overall roadway management including all access connections to the system;
  • Spot roadway management strategies that function to improve overall flow in the system;
  • Incremental implementation of synergistic applications; and
  • How these systems could be adapted to existing ITS and traffic operations investments commonly found on US freeways based on a phased approach.

4.1 Overall Roadway Management

The intent of this chapter is to document cases where synergistic relationships between traffic management strategies have been found; however, performance monitoring data regarding these strategies to date has been limited. Because this data is rarely stratified by strategy, being able to use it to estimate an individual strategy’s contribution to system level benefits is even more challenging. Nonetheless, research has shown that these strategies are rarely implemented in isolation, and a number of them are clearly complementary. While most of these strategies have some form of relationship with all of the others, there are some that stand out most clearly as complementary and/or supportive to a particular technique. Figure 10 indicates typical complementary and/or supportive strategies for each of the six European traffic management techniques. Note that while one technique may support another, the reverse is not always true. For example, while speed harmonization may be a critical supportive strategy for implementing hard shoulder running; hard shoulder running is not critical to the success of speed harmonization applications.

Figure 10. Relationships Between ATM Strategies

figure 10 - table graphic - This figure shows the relationships between ATM strategies.
Source: Parsons Brinckerhoff, 2009

A brief discussion of how these techniques could be applied in a synergistic manner is provided below. Not all combinations of complementary and/or supporting techniques are discussed, but the write-up provides a general idea of how certain strategies can work together.

Speed harmonization, for example, is often implemented in tandem with queue warning. Queue warning complements speed harmonization because in addition to warning drivers of downstream queues, it communicates the reason why speeds are being lowered. In Germany, a congestion pictograph or icon is displayed on both sides of the overhead gantries to alert motorists of queues or congestion ahead. The value of the system lies in warning drivers of downstream queues so they take appropriate actions (e.g., slow down or change lanes), thereby reducing the occurrence of primary and secondary collisions caused by the congestion. In the Netherlands, motorists are alerted of queues with flashing lights surrounding the variable speed limits, and speed harmonization is activated with variable speed limit signs.

Queue warning is valuable in that it warns drivers of downstream queues so they take appropriate action to slow down or change lanes, reducing the occurrence of primary and secondary collisions caused by congestion. Queue warning can be supported by the implementation of speed harmonization to further enforce the need to reduce speeds.

Hard shoulder running is frequently implemented in conjunction with both speed harmonization and queue warning, as well as with junction control because they share the common need of addressing recurring congestion in bottleneck locations. Limited data from the UK indicates how these techniques can build upon each other. Transportation professionals in the UK believe that using speed harmonization and queue warning is important in order to maintain safety during hard shoulder running operations. Since hard shoulder running removes the shoulder for use as a breakdown lane, having a robust incident management program in place to monitor and respond to incidents as soon as possible is essential. Where hard shoulder running begins or terminates at a ramp junction, junction control is often required to maintain lane continuity and safe operations.

Junction control may be enhanced when supported by ramp metering, particularly when used at freeway on-ramps. If the control strategy has changed a junction from an add-lane to a merge condition, ramp metering would be especially beneficial to break up platooning vehicles from entering a ramp and facilitate the merge condition. Dynamic re-routing can support junction control as well in that if the control strategy reduces capacity of one movement (e.g., the through movement) in favor of another movement (e.g., the exiting movement), then it may be beneficial to re-route some through movement traffic to alternate routes so as to not experience undue congestion.

Dynamic re-routing is highly dependent on traveler information (including queue warning) to not only direct drivers to the desired alternative parallel route, but to also inform them as to why they are being encouraged to reroute. Information could include projected travel times via alternative routes and reasons for the delay on the primary route, e.g., “accident ahead.” Junction control can also support dynamic re-routing by providing additional capacity to a particular movement that has been targeted for re-routing.

Ramp metering can be enhanced by queue warning and traveler information when used to address mainline congestion. These techniques can provide the driver with information on why the ramp meter rate is operating in a given manner, which can lead to more acceptance of the meter and higher compliance.

4.2 Spot Roadway Management Strategies

In many urban roadway networks, overall system capacity is governed by localized constraints, or “bottlenecks,” at a limited number of locations. Addressing these bottlenecks can make a significant improvement in overall system performance and reliability. Often times these bottlenecks cannot be physically expanded due to either prohibitive costs or environmental concerns. These conditions can also be present during construction where detours do not offer the capacity, performance or operational safety of the final roadway configuration.

Because traffic management techniques are generally less expensive than the physical expansion of facilities, it can more feasibly be used as a means of addressing these conditions. For example, various traffic management strategies have been applied in Denmark as a way of maintaining traffic flow during construction.

Hard shoulder running is one of the more effective traffic management techniques that can provide additional capacity on an as-needed basis to address bottleneck issues. For hard shoulder running to be truly effective, it needs to extend through the bottleneck location upstream of typical queues. Otherwise it is simply moving the bottleneck to a new location.

4.3 Incremental Implementation

It is important to consider the environment within which potential traffic management techniques will be implemented; for example, are ramp metering, service patrols, existing VMS, managed lanes, or other more US-based techniques already a part of the freeway management system? While these more traditional elements can be integrated into many traffic management techniques or strategies, careful consideration should be given to implementing traffic management techniques that lend themselves to being actively managed when the more basic traffic management systems are not in place. This is particularly relevant when considering the overall operation of the system and the demands it may place on existing traffic management center facilities and staffing requirements.

It is important to consider the overall system and plan for the best combination of traffic management techniques for the region or area under consideration. Many logical and synergistic combinations of techniques lend themselves to incremental implementation that improves effectiveness. The benefit of this is that it allows agencies to implement some applications sooner rather than later, building users’ experience and trust in the general traffic management concept prior to implementation of supporting techniques. Examples of techniques that have been implemented incrementally include speed harmonization, followed by hard shoulder running in the UK on the M42. Speed harmonization produces clear benefits to safety and operations – the inclusion of hard shoulder running in select locations increases the system’s ability to decrease congestion and improve overall operations and throughput. The European experience is filled with examples where an initial corridor was fully instrumented and monitoring demonstrated proven effectiveness before wider system applications occurred. This approach also allowed agencies to ‘learn from their mistakes” in refining the applications in order to improve performance and lower their investment costs.

The deployment of traffic management techniques that will be managed actively should be done considering logical operating segments within the system under consideration. Logical starting and stopping points based on travel patterns, freeway geometrics, observed operations of recurrent congestion or persistent queuing, and areas with higher than expected crash rates provide insight into areas where initial investigation and consideration of active management techniques may be warranted.

4.4 Adaptation to Existing US ITS and Traffic Operations Investments

Much of the following discussion is based on work conducted by the Washington State Department of Transportation. This dialog is illustrative of similar adaptations occurring in other states as of 2010.

Integration with Current ITS Infrastructure

Current traffic management systems require a variety of instrumentation and communication investments to make the system functional. Some of this equipment is multi-purpose serving a number of traffic management techniques (e.g., in-road or other forms of vehicle detection, CCTV, VMS, communications network/equipment, etc). In many cases new or augmented equipment specific to the desired traffic management technique would be required (e.g., variable speed limit signs for speed harmonization). If existing equipment, detection, or traffic management systems are in place, their functionality should be reviewed to determine if they can be used for both the original intent as well as the proposed traffic management technique(s) to obtain the greatest benefit from existing system investments. The traffic management system will be relying on accurate, reliable and continual input for the various traffic management application algorithms – maintaining a high level of reliability on detection is crucial.

The variable message signs used to support these techniques are similar to sign technology used elsewhere by state DOTs. However, the purpose and application of the VMS signs is different than what has been typically used, due to the over lane positioning of the speed harmonization signs, their size, mounting maintenance and access requirements. Once again, it will be important to assess the existing system capabilities, the requirements of the new system, and their subsequent integration. For example, some transportation management system software can communicate with NTCIP signs, making integration much easier than if proprietary communication protocols are used.

Institutional Issues

Institutional issues are challenges that can prevent proper implementation of active traffic management techniques, but instead of being attributed to technology or engineering, these issues are caused by regulatory, legal, financial, management, organizational, human, or physical resource concerns and constraints and can even vary by state and locale.

Institutional issues differ between Europe and the US in various respects. European agencies may be subject to less liability due to legal statutes; they are perhaps more attuned to experimenting because there is limited funding and few geometric options to widen or otherwise add capacity through expansion or new routes; and for many applications they have a longer (and successful) track record in active traffic management accepted by their political and public stakeholders.

  • Legal statutes and case law may limit US agencies’ interest in such concepts as hard shoulder running, since the effective pavement, when not traveled on, is supposed to provide a safe refuge for emergency parking. Many European freeways do not traditionally have paved shoulders on one or both sides of the mainline lanes. Providing ‘hard’ shoulders that are able to take all types of vehicle loads as traveled lanes during peak periods improves capacity and mobility while not adversely impacting safety if the shoulder is able to be adequately monitored.
  • Transportation policies within the US tend to favor more capital investment in the “hard” side road system, while operational investments in some European countries are the primary (and in many cases only) form of investment occurring outside maintenance needs. The institutional arrangements within Europe reflect both federal and regional provinces in the decision making roles, not unlike the federal/state/local relationships in the US.
  • The Netherlands countrywide investment in active traffic management, currently underway on all motorways, dates back more than 20 years to much earlier demonstrations that provided insight into successful deployment under specific conditions. Institutionalizing a network approach came from these corridor demonstrations. Adjacent countries have now borrowed such experiences and system approaches from each other and share common implementation schemes. As noted above, within the US most agencies have focused more on rehabilitation and expansion projects with less comparative investment in operations. And similar to the European experience, just as much downstream time from initial US applications of actively managed traffic techniques to widespread adoption may be required.

Because many of these strategies are relatively new to the US, some institutional issues may need to be worked out. Even inter-agency and intra-agency issues can present implementation obstacles. The difficulty with institutional issues is that there are no consistent approaches to resolve them. Some general institutional issues that can impact implementation of a wide variety of actively managed techniques in the US include the following:

  • Priority: for traffic management techniques to operate successfully and reach their full potential, the techniques must be given priority for funding, programming and maintenance.
  • Continued Funding for Operations and Maintenance: sustained funding is essential to operate and maintain a safe and effective traffic management strategy. Operational funding provides the necessary staff to monitor, control, and adjust a system. Maintenance of a system is also necessary for proper operations, and the threshold for maintenance reliability may need to be much higher for passive in-field systems that are predicated on public respect to be effective. Any expansion of a traffic management system will also require sufficient and ongoing funding. Some delivery strategies, including design-build-finance-operate-maintain procurements, have been employed to assure the level of maintenance required in European examples.
  • Continued Funding for Electronic Equipment: electronic components used in these systems have a shorter life cycle than typical components in highway transportation. A program for preservation is needed in addition to an on-going maintenance program.
  • Continuous Staffing for Traffic Management Center Operations: staffing hours at a TMC may need to be expanded in order to safely and effectively operate traffic management systems in an active manner. A benefit-cost analysis should be undertaken to determine if the collision and congestion reduction benefits of implementing a traffic management technique will off-set the expected capital and operations and maintenance costs.
  • System Monitoring and Evaluation: the use of effective monitoring and data collection allows implemented traffic management systems to be evaluated and improved. This would typically coincide with a performance monitoring program with set objectives and thresholds in order to effectively determine if the system is meeting its goals.
  • High Quality System Information: providing accurate and reliable information to the system is essential for the safe and effective implementation and operation of any management technique. This is necessary to earn drivers’ trust and compliance for the systems. Accordingly, the algorithms behind the strategies must operate in real-time, with abilities for the system to self regulate with minimum operator oversight except to confirm specific pre-set actions.
  • Public Education: increasing US driver familiarity with actively managed traffic techniques and systems, their purposes, and congested freeway safety requires an ongoing public information campaign.

Speed harmonization and hard-shoulder running may face additional institutional considerations in the US, such as the following:

  • Coordination with Enforcement and Emergency Response Agencies: for successful operation, the proposed management techniques should be discussed with the enforcement/public safety entities (e.g. state patrol) and other key stakeholders such as emergency responders. These agencies must understand the overall function of the management techniques and collaborate with the operating agency on enforcement protocols. Enforcement protocols and understanding are important for the implementation of a speed harmonization system due to the variable nature of the speeds over a length of roadway; enforcement may want to focus on more obvious or blatant speed violations. For hard shoulder running, enforcement must be vigilant due to the safety issues and emergency responders must understand how using the shoulder as a travel lane will affect their response times.
  • Enforcement Plan for Traffic Management Techniques: without enforcement, some of the traffic management techniques and strategies may not be as successful. It is vital that appropriate warnings and enforcement actions are taken for motorists who disregard the regulatory signing. Enforcement may add a cost component to implementation and operation. Public outreach efforts must work to reinforce the strategies and help foster public trust in the system. As an example, motorists need to learn that when the signs show a reduced speed limit that there is a good reason to slow down. With hard shoulder running, it is important that motorists understand when this technique is operational and when it is not. As such, appropriate warnings and actions must be taken for those who are not compliant.

Suggestions to Address Institutional Issues

Reaching solutions to a range of institutional issues, which allows for the successful implementation of a variety of traffic management techniques and systems, requires collaborative planning and development. To effectively implement traffic management techniques that are actively managed in the US the following actions are suggested (WSDOT ATM Concept of Operations Report, 2008):

  • Provide Continuous Operations: providing continuous hours of operations of most techniques that will be actively managed is recommended, especially for speed harmonization and queue warning. This will provide necessary activation and monitoring of the system. By operating the system any time it is needed, stakeholder acceptance and public trust is created.  Additionally, some legal liabilities may be reduced.
  • Outreach to Stakeholders and Public: informing stakeholders and the public regarding the purposes, benefits, operation and performance outcomes of traffic management strategies will also build trust in the investments.
  • Outreach to Government Officials: continued support of traffic management techniques and systems will require early involvement with key officials and stakeholders. Various elected and appointed public officials should be informed about the techniques and benefits, especially before including these techniques in funded programs and project budgets.
  • Coordinate with Law Enforcement and Key Partnering Agencies: law enforcement needs to be involved with the design and intended operation of actively managed traffic management systems in order to determine how the system can accommodate enforcement and how officials should enforce it. Other agencies may also be interested in how potential management techniques could affect traffic on their transportation networks as well.
  • Create a Concept of Operations Plan: for the purposes of design, outreach, and operations, a concept of operations plan will be required to provide clarity into how a system will operate. This plan also includes ITS integration and determining operational responsibilities.
  • Integrate with ITS Infrastructure: creating and implementing a plan for integration with ITS architecture will define the roles of individual traffic management techniques and ITS.
  • Improve Analysis and Review: proper monitoring of a operational network and comprehensiveness of a network model are beneficial for monitoring techniques and predicting the effect of proposed techniques.
  • Obtain Approval for Experimental Traffic Control Devices: as traffic management techniques that are dynamically managed are new to the United States and frequently rely on signage and control procedures that are not currently described in the MUTCD, steps for experimental approval should be taken when a project timeline is set in order to ensure approval when the system will be activated.
  • Collaborate with Other States and Partnering Agencies: several locales in the US are investigating and implementing the discussed traffic management techniques. Working with these states in gaining lessons learned can provide shared insight into how to address institutional and engineering issues.
  • Coordinate with TDM Efforts: often times personnel charged with developing TDM policy are compartmentalized from operations staff who would be implementing the traffic management techniques. Coordinating these and other congestion management tools so as to provide a holistic approach is likely to produce more effective results.