Active Traffic Management Feasibility and Screening Guide

Chapter 4. Identify Major Roadway Segments for Potential Active Traffic Management

Having identified potential ATM strategies that can help satisfy agencies' regional transportation goals and objectives and that conform to the type of roadway network, agency policies, and any potential legal constraints, the next step is to identify individual roadway segments where ATM strategies are likely to provide operational benefits. There are no hard and fast rules as to the length of these roadway "segments." A general rule of thumb is to use major interchanges and/or intersections—where traffic flow characteristics often change—as the termini for these segments; or perhaps to make the entire facility a "segment" in the case of a connecting roadway or spur.

This screening activity (as summarized in Figure 6) is envisioned as primarily a qualitative assessment using readily available information (e.g., CMP, corridor studies, and other existing information and reports), coupled with local knowledge of the ATM stakeholders.

4.1 Determine Level of Existing Transportation Systems Management and Operations and Intelligent Transportation System Deployment

Active Traffic Management: The Next Step in Congestion Management is the document (13) that summarizes the results of the 2006 European scanning tour, which essentially introduced many ATM strategies to the United States. This document's title represents the appropriate view for any agency considering ATM strategies. Congestion management activities involve numerous strategies and supporting ITS technologies. TSM&O can be viewed as forming a continuum of approaches and systems (as shown in Figure 7), starting with the more conventional (and primarily reactive) strategies such as time-of-day signal control, basic traveler information (e.g., radio and dynamic message signs (DMS), a few ramp meters at bottleneck locations, and incident response); and then to the more advanced and proactive (i.e., "smart") approaches as provided by ATM. The next step is to integrate all these individual strategies together (e.g., Integrated Corridor Management [ICM]) as part of an overall ATDM philosophy.⁸) These more advanced strategies and technologies build upon the preceding ones, creating a series of "steps."

Just because a roadway segment is experiencing significant congestion, safety, and/or environmental problems, it does not necessarily mean that ATM strategies are the optimum solution. Before considering advanced TSM&O approaches such as ATM, the more conventional operations strategies and supporting ITS technologies should already be in place and thoroughly used. Implementing or enhancing the more conventional TSM&O strategies, such as incident management and enhanced traveler information, may be more appropriate before implementing ATM strategies. In other words, the deployment of ATM strategies should represent the "next step" rather than a "quantum leap" for managing congestion and enhancing safety.

FIGURE 6. FLOWCHART. IDENTIFY MAJOR ROADWAY SEGMENTS FOR POTENTIAL ACTIVE TRAFFIC MANAGEMENT (ATM)

FIGURE 7. DIAGRAM. CONTINUUM OF OPERATIONS STRATEGIES (BASED ON MATERIALS FROM THE SECOND STRATEGIC HIGHWAY RESEARCH PROGRAM [SHRP2] L36 PILOT REGIONAL OPERATIONS FORUMS)

Moreover, having basic ITS infrastructure (e.g., detection, closed-circuit television [CCTV], communications and power) already in place will likely reduce the costs of deploying ATM. The current functionality should be reviewed to determine whether the existing ITS infrastructure can be used for both the original intent as well as the proposed ATM strategies to obtain the greatest benefit from existing system investments.

4.2 Identify Major Segments That Will Likely Benefit From Deploying Active Traffic Management

As has already been discussed, ATM strategies can provide significant benefits in terms of improved safety and reduced congestion, as well as other providing other positive attributes. Segments that have one or more of these issues are likely to benefit from ATM.

4.2.1 Safety Problems

Roadway segments where there are a historically large number of crashes and incidents relative to other segments, and the resulting non-recurrent congestion, are strong candidates for ATM. This increased level of crashes may be a result of recurring congestion patterns, sudden changes to prevailing conditions (e.g., horizontal or vertical curves), adverse weather (e.g., recurring fog, wind, snow or ice conditions), or some other reason. ATM strategy implementation likely will vary depending on the prevalence and type of crashes occurring at these locations (as is further discussed in Chapter 5). For instance, a queue warning or dynamic speed limit system may be appropriate if there is an increased incidence of rear-end or lane change crashes that occur near a specific location on the highway. Junction control may also be appropriate if there are large numbers of side-swipe or rear-end collisions at or immediately downstream of entrance ramps during certain times of day. Dynamic speed limits may help reduce crashes along roadway segments that experience frequent adverse weather (e.g., fog, wind, snow, and ice) causing safety hazards for drivers.

4.2.2 Recurring Congestion and Bottlenecks

Roadway segments with frequent recurring congestion are often excellent candidates for ATM strategies. This congestion may be caused by several conditions, including the following:

• High traffic volumes — Roadways where traffic volumes often approach capacity or persist for long durations may benefit from ATM such as DShL, ARM, and ATSC. This is especially true if future capacity expansion cannot be created because lack of construction funding, geometric or environmental constraints, or because creating new full-time capacity does not conform to state, regional, or local policy.(4) A related consideration is the extent to which the congestion is directional—heavy in one direction one part of the day, heavy in the opposite direction during another period—a scenario that might benefit from dynamic lane reversal.
• Capacity-reducing bottlenecks — Bottlenecks, especially lane reductions, weaving and merging areas at ramps, and other geometric bottlenecks, reduce capacity and cause congestion. Using dynamic shoulder lanes, dynamic junction control and/or adaptive ramp metering during peak periods may be beneficial at bottlenecks to increase capacity and reduce the resulting congestion. Additionally, strategies like dynamic speed limits, dynamic lane assignment and queue warning could be potential applications that can reduce shock waves in traffic and warn of oncoming congestion, smoothing traffic flow before reaching an affected area.(4)

4.2.3 Other Considerations

Other situations that might highlight (or conversely diminish) roadway segments for potential deployment of ATM include the following:

• Transit operations — ATM strategies are especially beneficial within corridors in which transit is a major component and whose operations are subject to high variability (e.g., schedule adherence). Transit use can be improved by providing time savings and reliability to its users. ATM strategies that reduce the instability in traffic flow, like DSpL and DJC, may help stabilize traffic flow and enhance reliability. Similarly, transit-oriented ATM strategies, such as bus-only shoulder lanes (a form of DShL) and transit signal priority, may further enhance transit operations.
• Construction activity and opportunity — Ongoing or planned construction activities may influence ATM feasibility and implementation priorities. ATM strategies may be deemed more feasible or at least ranked higher for implementation if the opportunity exists to piggyback the installing ATM infrastructure on current or planned construction activities in corridor segments where ATM strategies are desired. ATM strategies may also be used as part of the overall maintenance and protection of traffic plans—for example, implementing DSpL, DLA, and/or QW on the approaches to a long-term work zone; implementing DShL, ATSC, and/or TSP along parallel facilities that will be used as alternative routes and/or modes for traffic diverting around the construction area; and implementing dynamic merge control at lane reduction points. Implementing ATM strategies as part of a larger roadway construction project may expedite implementation and possibly reduce costs. At the same time, a major roadway reconstruction project involving geometric changes may impact the need for ATM concepts and strategies, possibly resolving safety and/or congestion issues or relocating such traffic problems to other segments of the network following construction.
• Integrated Corridor Management — A corridor consisting of multiple and parallel networks (e.g., freeway, managed lanes, arterial) and/or modes (e.g., bus, rail) may benefit from ATM in the context of ICM. The goal of ICM is to optimize using existing infrastructure and leverage underutilized capacity on major multinetwork corridors. Several potential ICM strategies identified in the ICM Implementation Guidance (24) encompass the dynamic use of ATM strategies, including dynamic speed limits, lane use control, dynamic shoulder lanes, dynamic lane reversal, transit signal priority, and dynamically modifying ramp metering rates and arterial signal timing.
• Roadway geometrics — The width, location, and continuous length of shoulders, on the mainline and on ramps, will impact the feasibility of dynamic shoulder lanes and junction control, while ramp configurations and storage may impact the ability to implement ramp metering (additional details are provided in the next chapter).
• Roadway use — The primary use of the roadway segment may be considered as part of the screening and prioritization. Examples in this regard include whether the roadway serves special event venues and/or recreation areas with the resulting variations (often significant) in traffic volumes, whether the roadway serves major economic areas or major freight and intermodal facilities (with the resulting commercial vehicle traffic), or whether a roadway is used as an evacuation route. The existence of managed lane facilities (e.g., HOV, HOT) may also be considered.
• Data availability — Certain data are required to quantitatively assess the applicability and benefits of various ATM techniques (see Table 11). Data availability might be an important consideration when screening candidate roadway segments and/or links and when establishing a baseline from which the benefits of ATM can be compared. Practitioners should assess the availability and possibility of acquiring the necessary congestion, safety, and other information needed to demonstrate ATM benefits. Demonstrating positive performance will help gain the needed support to move ATM into the next stages of the regional transportation planning process or the systems engineering process (e.g., Concept of Operations and requirements), leading to deploying ATM strategies or expanding current ATM systems in the future. If acquiring the needed data for certain roadway segments is not feasible, then justifying implementation of ATM at these locations relative to other transportation investments may not be possible.
• Institutional considerations — Implementing ATM strategies will likely require significant coordination with outside agencies, such as police and other enforcement entities, other transportation providers (e.g., toll and bridge authorities), MPOs and other planning groups, local jurisdictions, and transit agencies. Some roadway segments may require more such interagency coordination than others. The screening process may consider the amount of coordination required for each segment (or series of segments), identifying if there are any concerns that exceed those generally expected for all segments. Having the support of decision-makers and an ATM champion in the lead agency and other involved agencies may also be considered.

4.3 Segment Screening Examples

The approach taken by a number of agencies, including WSDOT, California Department of Transportation (Caltrans), and New Jersey DOT (NJDOT), has been to develop a screening matrix with the roadway segments listed horizontally and a variety of screening criteria listed vertically. Several different approaches exist for filling in the matrix as discussed below. The scoring effort can be performed as a workshop activity, or a smaller group can prepare a draft screening matrix and send out to the other stakeholders for review and comment, followed by a meeting to discuss and finalize.

4.3.1 Washington State Department of Transportation

WSDOT (25, 26) and their consultant (Parsons Brinckerhoff) established a set of screening criteria to select candidate corridors in the Seattle area where ATM strategies could be applied. The project team then qualitatively assessed each freeway corridor based on these criteria: a scale of 0, 1, and 2 to designate high potential (2), moderate potential (1), and no potential (0) for each segment with respect to each criterion used, with a comparison matrix used to aid in the screening process. Speed, congestion, and collision data and patterns were reviewed to target specific locations; potential ATM strategies were reviewed to determine whether implementing them would mitigate the existing congestion or crash patterns. ATM opportunities were also noted by strategy and location in the matrix for each corridor.

A corridor screening workshop was conducted during which the project team described ATM strategies, the screening criteria, methodology, and results of the initial screening to members of WSDOT, the Washington State Patrol, and the MPO. The workshop participants participated in a roundtable discussion of each corridor's particular roadway and traffic attributes, as well as the potential to implement ATM techniques based on the screening criteria. The group discussed the initial ratings and the unique aspects of each corridor. Discussions ranged from the need to consider the effect of corridor impacts on the entire system to the location of specific junction control possibilities. Figure 8 presents the modified individual and summary ratings for each corridor.

FIGURE 8. TABULATION. CORRIDOR SCREENING RESULTS (WASHINGTON STATE DEPARTMENT OF TRANSPORTATION [WSDOT]) (26)

4.3.2 California Department of Transportation

Caltrans District 7(27) other regional stakeholders, and their consultant (Cambridge Systematics) established a set of screening criteria to select a corridor for initial ATM implementation within the Los Angeles metropolitan area. The qualitative assessment used descriptive terms such as "very high/very good," "high/good," "moderate," "poor," "none," and "unknown" to rate corridors and fill out the matrix, followed by an overall assessment at the bottom as shown in Figure 9. The 17-mile Interstate 105 (I-105) corridor was subsequently selected for more detailed analyses and subsequent implementation.

FIGURE 9. TABULATION. CORRIDOR SCREENING RESULTS FOR CALIFORNIA DEPARTMENT OF TRANSPORTATION (CALTRANS) DISTRICT 7 (27)

4.3.3 New Jersey Department of Transportation

NJDOT, New Jersey Institute of Technology (NJIT), other statewide stakeholders, and their consultant (CH2M HILL) performed a preliminary screening of all the limited access roadways in New Jersey owned and managed by NJDOT—the initial step in a project to identify an initial ATM deployment area in the state and prioritize other potential ATM projects (28). A set of screening criteria were identified and grouped together in terms of existing ITS/TSM&O, traffic flow considerations, and other use considerations as shown in Figure 10. Preliminary scoring was conducted based on input and local knowledge of former NJDOT staff on the project team, coupled with a review of maps (provided by NJIT and NJDOT) that identified congested corridors, high crash locations and rates, major bottleneck locations (in terms of delays and frequency of occurrence), ITS/TSM&O deployment (e.g., available conduit, service patrol coverage, DMS, and TRANSMIT readers) and designated high growth areas in the state. The segments were scored for their TSM&O/ITS capability as follow:

• 10: Segment fully instrumented and operated/managed.
• 5: Segment partially instrumented and operated/managed.
• 0: Segment has minimal TSM&O or no instrumentation.

Those segments that had mostly 5s (or less) for their ITS-related scores (highlighted in yellow in Figure 10) were not considered good candidates for the initial deployment of ATM relative to the other segments in the state that had greater ITS infrastructure and TSM&O-related activities.

FIGURE 10. TABULATION. SEGMENT SCREENING RESULTS FOR NEW JERSEY DEPARTMENT OF TRANSPORTATION (NJDOT) ⁹ (28)

Traffic flow considerations addressed safety and congestion. These traffic-related were scored as follows (with the highest point structure given the importance of these criteria):

• 15 to 20: Significant issue, problem, or need within this segment (relative to others in the state).
• 10: Moderate issue, problem, or need within this segment (relative to others in the state).
• 0 to 5: Minor issue, problem, or need within this segment or no issue at all (relative to others in the state).

Those segments with a maximum score of 20 in either the safety or recurrent congestion areas (highlighted in "green" in the spreadsheet) were identified as strong candidates for ATM. The other use considerations—such as special event traffic, commercial traffic, severe weather concerns, evacuation route, and potential ICM corridor—were scored as follows:

• 5: The segment provides this current/potential use.
• 0: The segment does not provide this current/potential use.

All scores for safety, recurrent congestion, and other considerations were then totaled (except for those segments eliminated from consideration due to the lack of sufficient ITS and/or TSM&O). These total scores were used to identify any additional segments that were not previously identified for more detailed analysis as part of the safety and recurring congestion analysis. These segments (highlighted in blue in Figure 10) might be candidates for ATM, but not as high priority as the other segments highlighted in green.

The next chapter discusses screening criteria for taking roadway segments and corridors designated as potential ATM locations and identifying specific links and strategies.

⁸ And one can only surmise where this operations continuum will lead in the future with Connected Vehicles, automated driving functions, "big data" and predictive capabilities.

⁹ This is only a partial representation. In all, 24 different segments were evaluated.