16.0 Transportation Systems Management and Operations
- 16.1 What Is Included?
- 16.2 Why Address GHG in TSM&O?
- 16.3 Level of Effort
- 16.4 Complementarity/Consistency with Other Transportation Goals
- 16.5 Who—Roles and Responsibilities
- 16.6 Inventory Development
- 16.7 Goal and Target Setting
- 16.8 Strategy Identification
- 16.9 Strategy Evaluation
- 16.10 Implementation
- 16.11 Monitoring, Evaluation, and Reporting
- 16.12 Self-Assessment: Transportation Systems Management and Operations
16.1 What Is Included?
This section discusses how greenhouse gas (GHG) emissions from the transportation system can be addressed through a State department of transportation’s (DOT’s) transportation systems management and operations (TSM&O) activities. According to the American Association of State Highway and Transportation Officials’ (AASHTO’s) The Transportation Systems Management and Operations (TSM&O) Guidance, TSM&O is a set of strategies to anticipate and manage traffic congestion and minimize the other unpredictable causes of service disruption and delay, thereby maintaining roadway capacity while improving reliability and safety (AASHTO, 2014). Strategies combine intelligent transportation system (ITS) information and control communications infrastructure with related field procedures and protocols within a specific operational concept. This operational concept is designed to anticipate and mitigate the impacts of the various causes of congestion, both recurring and nonrecurring.
16.2 Why Address GHG in TSM&O?
TSM&O activities are one of the most effective strategies under the DOT’s direct control for reducing emissions. GHG system emissions are basically a function of vehicle miles traveled (VMT), vehicle mix, and speed and acceleration profiles. Internal combustion engine vehicles operate most efficiently while traveling at relatively constant speeds within a moderate speed range. Low-speed travel, frequent acceleration, and idling—typical characteristics of congested conditions—increase fuel consumption and GHG emissions. Operation at very high speeds also increases emissions. Figure 16.1 gives an illustrative profile of the relationship between travel speeds and GHG emissions and the role of traffic operations strategies in reducing emissions.
Figure 16.1 Speeds versus Emissions
Reducing congestion through TSM&O can reduce emissions without requiring travelers to change their behavior or purchase different types of vehicles. Traffic flow improvements that reduce emissions also typically benefit travelers in other ways—time and reliability savings and possible safety benefits from reduced stop-and-go traffic. These strategies can be a “win-win” for mobility, the economy, and the environment.
While TSM&O strategies generally reduce emissions in the short term, there may be some longer-term offsetting effects if travel time savings lead to “induced demand” that increases overall travel. Methods of accounting for induced demand are discussed in Section 14.9.
16.3 Level of Effort
A State DOT already typically has a variety of TSM&O responsibilities, such as
- Developing a congestion management plan or process or working with metropolitan planning organizations (MPOs) on their plans.
- Retiming traffic signals.
- Operating incident management programs.
- Planning and deploying ITS infrastructure such as real-time traffic information signs and broadcasts, adaptive signal control, ramp metering, and integrated corridor management systems.
- Operating traffic management centers to actively manage traffic conditions.
- Operating managed lanes.
- Managing work zones, special events, and severe weather response.
Considering GHG emissions in TSM&O may cover a spectrum, from simply measuring the benefits of what already is being done to optimizing current operations for GHG emission reduction to expanding TSM&O activities with a focus on emissions as well as congestion reductions (Figure 16.2).
Figure 16.2 Strategies of GHG Consideration in TSM&O
The level of effort can range from modest (a few tens or hundreds of staff hours to estimate current reductions with sketch methods such as speed-based emission factors) to substantial (involving the investment of a significant fraction of capital and operating funds for the deployment of new operations strategies to reduce emissions).
16.4 Complementarity/Consistency with Other Transportation Goals
Strategies to reduce congestion can have substantial safety and mobility benefits for travelers. These strategies can also have economic benefits by improving general mobility, workforce accessibility, and regional attractiveness and reducing congestion for freight and other commercial vehicle travel. Operational strategies that reduce GHG emissions will also typically reduce emissions of criteria pollutants and other pollutants of concern, thereby improving overall air quality and human health. Projects funded by the Federal Congestion Mitigation and Air Quality (CMAQ) Improvement Program that are focused on traffic operations will usually have GHG as well as air quality benefits.
16.5 Who—Roles and Responsibilities
A State DOT typically has responsibility for TSM&O strategies on Interstate and State highways and may support local jurisdictions or traffic management organizations in implementing TSM&O on local roads. Internal roles typically include:
- TSM&O operations within a DOT are usually directed from a central “Traffic Engineering” and/or “Safety” Division within the Operations, Maintenance, or Engineering unit. Central office functions typically involve technical direction and support on ITS, traffic operations, management, information, and safety. This office also acts as a policy liaison with external traffic police organizations and coordinates internally with agency departments such as Planning, Budgeting, and Engineering. Day-to-day operational matters are sometimes managed through regional traffic management centers, but most often these matters are managed through the local Regions/Districts.
- Staff of the Environmental unit would typically support TSM&O staff in liaison with environmental agencies, estimating emissions by providing emission factors or performing emissions calculations based on data collected through TSM&O systems.
- Staff of the Planning and Programming units may also be involved in evaluating and prioritizing TSM&O strategies as part of long-range planning, budgeting, programming, and project development—which may include consideration of the GHG benefits of these strategies. See Statewide Opportunities For Linking Planning and Operations: A Primer for more information on linking planning and operations (FHWA, 2008).
External partners can also be key stakeholders in implementing TSM&O strategies. Effective operation of the transportation system typically requires coordination among multiple entities, including the State DOT; county and municipal transportation departments; and other facility operators such as toll road authorities, transit operators, and law enforcement and emergency response agencies. A task force or working group may exist to coordinate these agencies’ activities and optimize operations for the transportation system as a whole. GHG reduction objectives, strategies, considerations, and reporting may be coordinated through this group.
16.6 Inventory Development
Total emissions from highway vehicles can be estimated in an inventory using various methods that are described in Section 9.0. The tools and methods used for highway emissions inventories may account for the emission reductions provided by existing TSM&O strategies, through the calibration of overall fuel consumption or emissions to observed conditions. However, these systems-level tools and methods typically do not provide the detail needed to evaluate the effects of specific operational strategies. Operations-specific evaluation methods as described below may be needed. Emission rates, as well as the response of emissions to traffic operations strategies, will vary across vehicle types. At a minimum, different GHG emission rates should be considered for up to six vehicle classes consistent with those for which traffic classification counts are reported to FHWA for the Highway Performance Monitoring System (HPMS), as shown in Column 1 of Table 16.1. More detailed evaluation of emissions may consider additional vehicle classes, such as the 13 source types defined in the Motor Vehicle Emission Simulator (MOVES) 2014 model, which nest within the HPMS vehicle types.
Table 16.1 Vehicle Types for Emissions Analysis
|HPMS Vehicle Type||MOVES Source Type|
|Passenger Car||Passenger Car|
|Other Four-Tire, Two-Axle||Passenger Truck|
|Light Commercial Truck|
|Single Unit Trucks||Refuse Truck|
|Single Unit Short-Haul Truck|
|Single Unit Long-Haul Truck|
|Combination Trucks||Combination Short-Haul Truck|
|Combination Long-Haul Truck|
For strategies that may encourage mode shift, such as multimodal traveler information and bus priority treatments, the GHG impacts of mode shifting should be considered in addition to any effects of traffic flow changes.
Some TSM&O strategies may result in a very modest increase in emissions to implement the strategy itself. Examples could include the power consumed in operating a traffic management center or the fuel consumed by incident response vehicles. However, these effects are typically small compared to emissions from transportation system users as a whole and will be outweighed by the savings in GHG emissions from the operation of the facility. Emissions from facilities and vehicles to implement TSM&O strategies can be considered using the data sources and methods described in Section 9.9.
16.7 Goal and Target Setting
When tracking overall emissions from transportation system users, it can be difficult to isolate the overall emissions changes attributable to TSM&O strategies from the effects of other changes that occur in transportation conditions, such as overall travel demand, shifts in demand by location and time of day, and improvements to the efficiency of vehicles. It may be more productive to focus target setting within the TSM&O functional area on incremental improvements for which reductions can be measured. An example would be achieving a GHG reduction of X metric tons per year through implementation of CMAQ-funded projects and/or other TSM&O projects for which GHG benefits can be estimated. However, it will be important to place this estimated contribution in the context of agencywide or statewide targets for transportation system GHG reduction.
16.8 Strategy Identification
The AASHTO TSM&O guide (AASHTO, 2014) provides examples of best-practice TSM&O strategies along with their general effectiveness for improving energy and the environment, as shown in Table 16.2.
Table 16.2 TSM&O Strategies and Environmental Effectiveness
|TSM&O Strategies||Relative Effectiveness|
|Traffic Incident Management||High|
|Safety Service Patrols||High|
|Traffic Signal Optimization/Retiming||High|
|Traffic Adaptive Signal Control||High|
|Electronic Toll Systems||High|
|Electric and Alternative Fuel Vehicle Recharging/Refueling Stations||High|
|Traveler Information and Incentive Apps||High|
|Road Weather Information Systems||Medium|
|Work Zone Management Systems||Medium|
|Ramp Metering Systems||Medium|
|Electronic Border Crossing Systems||Medium|
|Commercial Vehicle Information Systems||Medium|
|Bus Rapid Transit||Medium|
|Transit Signal Priority||Medium|
|Transit Automated Vehicle Locator/Computer-Aided Dispatch||Medium|
|Managed Lanes (including clean vehicle incentives)||Medium|
|Traveler Information/Dynamic Message Signs||Low|
|Parking Management Systems (esp. to encourage transit usage)||Low|
Source: Adapted from Investment Opportunities for Managing Transportation Performance through Technology (U.S. DOT, 2009) as reprinted in The Transportation Systems Management and Operations (TSM&O) Guidance (AASHTO, 2014), with some additions and minor modifications.
The Active Transportation and Demand Management Implementation and Operations Guide (FHWA, 2017) provides information on the use of available tools and assets to manage both traffic flow and demand. Examples include adaptive traffic signal control, dynamic lane use control, and dynamic speed limits.
16.9 Strategy Evaluation
Table 16.3 provides an overview of tools and methods that currently are available to support emissions estimation for TSM&O strategies. It is important to consider that the emissions reduction estimates for these strategies will only be as good as the information available on changes in traffic operations. For ex ante project evaluation, major projects sometimes have microsimulation model data available that can be used to estimate emissions changes. Smaller projects will rarely have such information available, and sketch-level estimates may be required based on estimated changes in project speeds or observed changes for similar projects.
For projects that are not expected to affect traffic volumes or cause mode shifts, a simple calculation can be performed:
Δ Emissions = Annual average daily traffic (AADT) * Segment Length * (EFspeed2−EFspeed1)
Where Δ Emissions is summed across vehicle types and time periods (e.g., peak and off-peak, which may have different speeds), and EF is the emission factor (grams per vehicle-mile) at speed x for a given vehicle type. Air quality or environmental staff may be able to provide a table of emission factors by speed and vehicle type to assist in this calculation.
For strategies that encourage mode shift from auto to transit without adding transit service (e.g., due to faster transit operations or better information), a basic equation such as the following may be used to estimate the GHG effects of mode shifts:
Δ Emissions = New Transit Riders * Prior Drive Mode Share * Average Trip Length * EFauto
Where Prior Drive Mode Share is the fraction of new riders who would have driven a car (or ridden as the primary occupant of a taxi or ride-hailing vehicle). New Transit Riders could be estimated through observed data (ex post evaluation), ridership elasticities (percent change in ridership with respect to percent change in travel time), or with a model that predicts mode shift.
Another source of information on TSM&O emissions effectiveness is the ITS Benefits Database, which documents findings from ITS deployment evaluations on the effect of ITS on transportation systems performance and provides convenient access to typical benefits of ITS deployments.
Table 16.3 Evaluation Tools and Methods for TSM&O GHG Reduction Strategies
|Method or Tool||Uses for TSM&O Strategy Evaluation|
|FHWA CMAQ Emissions Calculator Toolkit and California Air Resources Board (CARB) SB1 Grant Program Emissions Calculator||Sketch tools to estimate emissions benefits of projects funded using CMAQ or other air quality improvement funds. Tools include traffic flow improvement projects, based on changes in traffic speeds and volumes by vehicle type. FHWA tools provide somewhat more functionality than CARB tools.|
|GreenDOT||Spreadsheet tool that includes a module for traffic smoothing strategies.|
|U.S. EPA MOVES||EPA-approved emission factor model for use in 49 States. May be run in project mode using average speed, drive cycles, or operating mode distribution inputs to estimate changes in emissions as a result of changes in traffic flow conditions. (Speed changes need to be estimated through another method such as field observations or volume-delay formulas.)|
|CARB EMFAC model||CARB-approved EMFAC model for use in California. Functionally similar to MOVES.|
|Volume-delay functions||Establishes a relationship between volume, capacity, and vehicle speed; can be used as a sketch-level estimation of speed changes from capacity increases (or equivalent operational effects)1 to apply to speed-based emission factors.|
|Microsimulation model emissions output||Detailed modeling of traffic flow conditions based on roadway geometry, traffic control operations, and vehicle mix. May be conducted to evaluate major capacity or operations project alternatives. Some microsimulation models may provide emissions or fuel consumption as a direct output.|
|VisionEval/EERPAT||Planning-level model that considers deployment of a variety of traffic operations strategies (freeway and arterial management, ramp metering, incident management). Intended for regional, not project-specific, analysis. Accounts for effects of vehicle technologies and induced demand.|
1 There are some methods for translating operations improvements into equivalent capacity increases built into the FHWA HERS model. See the HERS documentation published by FHWA.
GHG-reducing TSM&O strategies would normally be implemented as part of an agency’s day-to-day TSM&O responsibilities. Additional activities may be added to estimate GHG emissions reductions and consider these impacts in strategy prioritization and design. In addition, GHG-focused strategies may be added to an agency’s TSM&O work program, for example, implementing bus priority treatments at intersections.
16.11 Monitoring, Evaluation, and Reporting
Transportation agencies are increasingly moving towards incorporating performance measurement into all facets of their operations. The AASHTO TSM&O guide provides guidance for moving through the various TSM&O capability maturity levels (1 through 4) on performance measurement (AASHTO, 2014). GHG emissions can be incorporated as part of the agency’s TSM&O performance measurement activities consistent with the usual “Plan, Do, Check, Act” approach illustrated in Table 16.4.
Table 16.4 GHG Management Cycle: TSM&O
|Plan||Set policy||Establish targets||Make assignments|
|Do||Develop procedures||Train staff||Implement|
|Check||Report||Consolidate reports||Evaluate performance|
|Act (Improve)||Check in agencywide||Explore alternatives||Revise procedures|
Source: Adapted from Using an Environmental Management System to Meet Transportation Challenges and Opportunities: An Implementation Guide (AASHTO, 2003) and Beyond the Short-Term—Transportation Asset Management for Long-Term Sustainability, Accountability and Performance (FHWA, 2010b).
GHG-reducing activities and outcomes from TSM&O projects and programs can also be reported back to Central Administration, Planning, Environmental, or other units charged with overall reporting of GHG reduction activities and benefits across the agency. These may include process-based measures (e.g., consideration of GHG in strategy evaluation), output-based measures (e.g., number of signals retimed), and outcome-based measures (actual emissions reduced or emissions per dollar). These in turn may be used to plan future investments for GHG offsets along with possible mobility and safety improvements.
Since it is difficult to directly observe GHG emissions from vehicles, monitoring and evaluation of TSM&O effects on GHG emissions may require a combination of observed data (e.g., changes in traffic conditions as a result of a project) and modeled data (e.g., emission factors relating emissions to those traffic condition changes). Modeling/analysis methods may be used to estimate the emission reductions from the entire portfolio of an agency’s projects, while field measurements on sample projects can help to confirm the validity of the models and provide project-specific traffic data.
Monitoring of TSM&O projects should consider the timeframe after which the project is implemented. For example, benefits of signal retiming may degrade over time as traffic patterns change. Regular retiming of signals may be needed to sustain GHG benefits over the long term. Guidance states that signals should be retimed every 2.5 to 3 years and that most agencies retime signals within a 5-year period (Gordon, 2010).
Table 16.5 Estimates of TSM&O GHG Cost-Effectiveness
|Source||Description||Location/Scale and Timeframe||Capital Cost||GHG Reduction, Tons, Annual||Annual $/Annual Ton||Annual Tons/Annual $ Millions1|
|Moving Cooler||Ramp metering||U.S., 2020–2050||$1.3B||680,000||50||21,000|
|Advanced traffic management/
integrated corridor management
|Cambridge Systematics, Inc., and Oregon Systems Analytics (2016)||ITS strategies (per EERPAT analysis)||Massachusetts||(3,000)||NA||NA|
|ITS Benefits Database||Advanced traffic signal control||Pittsburgh||$683,000||558||1202||1202|
|Corridor traffic signal optimization||Allegheny Co, PA||$30,500||666||52||72,0002|
|Baker and Khatani (2017)4||Traffic operational improvements||Massachusetts (94 projects)||$3,080,000||76||8603
|Peters et al. (2009)5||Traffic signal retiming||Portland, OR||$3,500 per intersection $530,000 for 135 intersections||50 per intersection 15,000 for 135 intersections||4–7||143,000–283,0002|
Notes: Moving Cooler: An Analysis of Transportation Strategies for Reducing Greenhouse Gas Emissions (Moving Cooler) and Application of the Energy and Emissions Reduction Policy Analysis Tool (EERPAT) Greenhouse Gas Analysis Tool in Massachusetts: Final Report [Cambridge Systematics, Inc., and Oregon Systems Analytics, 2016] considered induced demand. The project-specific evaluations cited did not consider induced demand.
1 Cambridge Systematics, Inc., calculations based on source document data. Note that these estimates are provided for order of magnitude only; no consideration is made to adjust to the same year dollar values, discounting, or adjustment of emission rates as fleet efficiency changes.
2 Annual $/ton and tons/$ million estimate calculated by Cambridge Systematics, Inc., assuming 10-year project life.
3 Report authors’ calculation assuming a 50-year project life.
4 Baker, E.D., and S.N. Khatani (2017). Developing a Metric for the Cost of Green House Gas Abatement. Prepared for Massachusetts Department of Transportation, University of Massachusetts Transportation Center Report 17.01.
5 Peters, J., R. McCourt, and R. Hurtado (2009). Reducing Carbon Emissions and Congestion by Coordinating Traffic Signals. ITE Journal, April 2009.
16.12 Self-Assessment: Transportation Systems Management and Operations
A self-assessment worksheet is provided to help State transportation agencies assess their current level of engagement with GHG in TSM&O and determine next steps for increasing their level of engagement.
Click to download – Self-Assessment: 16.0 Transportation System Management and Operations