Incorporating Travel-Time Reliability into the Congestion Management Process (CMP): A Primer

Chapter 4. Model Congestion Management Plan

This chapter provides a model Congestion Management Plan (CMP) that demonstrates how reliability can be incorporated at appropriate steps. Addressing reliability and non-recurring congestion enhances and expands upon the current state of the practice for most CMPs. The model CMP is not intended to be a complete document; it is an assembly of excerpts intended to provide insight for metropolitan planning organization (MPO) developers of CMPs.

4.1 One Size Does Not Fit All

Each MPO operates in a unique circumstance, so this model CMP should be used as guidance and be considered in relation to your region's population, funding, governance, transportation system priorities, data availability, and staff capacity. Even if your MPO does not assign a high priority to congestion mitigation, or has a modest level of recurring congestion, the public and their elected officials may be supportive of improving the reliability of travel time by addressing non-recurring congestion.

4.2 Model Plan Excerpts

The following section shows examples of the different CMP components and how reliability can be integrated.

This section covers:

Goals and Objectives
Performance Measures
Monitoring Plan
Problem Identification
Identification of Strategies
Implementing Strategies and Monitoring Strategy Effectiveness

Goals and Objectives

Establishing goals and objectives is the first substantive step in the CMP and a key entry point for consideration of reliability.

MPOs enumerate their goals and objectives in the metropolitan transportation plan (MTP), including decisions on how to treat congestion mitigation and non-recurring congestion. The CMP should incorporate these goals and objectives, rather than create a new set of priorities.

The following excerpt from the Binghamton (NY) Metropolitan Transportation Study's 2035 Plan [13] is an example that gives priority to operational solutions:

Mobility Goal

To create a regional transportation system that provides travel choices so personal travel and goods movement can maximize efficiency.

Mobility Objectives

1. Invest in strategies to provide travel choices and alternatives to single-occupant vehicle personal travel
(1.1) Improve the availability and level of service of public transit
2. Invest in strategies that improve the efficiency of vehicle travel
(2.1) Complete the deployment of the ITS Regional Architecture
- Robust traffic and transit management center
- Pervasive traveler information systems
- Best available traffic signal system technology
- Incident management on all principal arterial highways
(2.2) Participate in statewide and bi-state efforts that support ITS Advanced Commercial Vehicle Operations
(2.3) Address congested areas with appropriate measures, including
- Improving traffic signal timing
- Transportation systems management strategies

ITS = Intelligent Transportation Systems

Source: Binghampton Metropolitan Transportation Study's 2035 Plan, page 15

The North Central Texas Council of Governments in Dallas-Fort Worth demonstrates how a goal from the MTP related to system operations can lead to objectives for improving operations and reliability can be translated into the CMP [14]:

CMP Goal and Actions

Goal: Identify quick-to-implement low cost strategies and solutions to better operate the transportation system

Action: Implement quick-to-implement low cost strategies and solutions to better operate the transportation system

Objectives

Reduce SOV trips through travel demand strategies
Provide all users with travels alerts and alternative routes in the case of incidents, special events, weather, construction, and severe congestion at choke points.
Increase the number of intersections that are equipped and operating with traffic signals that enable real-time monitoring and management of traffic flow.
Reduce mean roadway clearance time per incident (defined as the time between awareness of an incident and restoration) of lanes to full operational status

SOV = Single occupant vehicle

Source: North Central Texas Council of Governments in Dallas-Fort Worth CMP (2013), Exhibit III-6

Performance Measures

Objectives are supported by performance measures that are used to track and demonstrate outcomes of projects and actions that are designed to improve reliability.

Moving Ahead for Progress in the 21st Century Act (MAP-21) establishes a paradigm of performance-based planning and programming (PBPP) for MPOs, transit operators, and state departments of transportation (DOTs). They will be required to be accountable for their investment decisions by measuring the results of project and programmatic actions. Performance measures must be credible and easily understood by the public and MPO decision-makers. "Did the money we spent on the Enhanced Incident Management Program improve travel-time reliability as much as we forecasted?" Below is an example from the Delaware Valley Regional Planning Commission in Philadelphia, emphasis added, where speed drop duration was analyzed over time to identify periods of non-recurring congestion.

Reliability

Archived operations data available through the I-95 Corridor Coalition Vehicle Probe Project was used to develop a criterion that measured reliability. The specific measure analyzed was duration of congestion on all freeways and select arterials in the region. The criterion identified road segments during the 5:00 to 6:00 PM peak hour, when travel speeds dropped below 70 percent of the posted speed limit, as well as the duration of the speed drop. This analysis produced a more robust measure of reliability than what was possible in past iterations of the CMP.

Source: Delaware Valley Regional Planning Commission

The Madison Transportation Planning Board's CMP [15] proposes a larger set of performance measures related to reliability. The existing measures highlight causes of non-recurring congestion, and therefore are only secondary indicators of reliability. The preferred measures, to be developed, are a more direct metric. Because the CMP is a continuous process, it is acceptable to define measures that can be developed to improve understanding of outcomes. In this case, the MPO shows the resource requirements in terms of capital funding and human effort for the proposed measures, summarized below in Table 11 from page 40 of their CMP.

Table 8. Example of Resource Requirements for Performance Measures from Madison, Wisconson

Principal Arterial Freeways -Type III (Non-Recurring Congestion)

Measure	Required Resources	Extent/ Coverage	Update Frequency	Credibility	Public Understanding	Decision making
Crash reports	Currently used	High	Ongoing	High	High	Low
Service patrol reports	Currently used	Low	Low	Modest	High	Low
Travel time index (TTI)	Capital: Programmed Human: Medium	Complete freeway coverage	3 years	High	High	Medium
Incident index	Human: High	Complete freeway coverage	Annually	High	High	High
Congestion duration	Capital: Programmed Human: Medium	Complete freeway coverage	Tri-annually	High	High	Medium

Note: Congestion duration is an important companion measure to TTI, indicating to travelers and decision makers the extent of the peak-period during which a poor TTI may be encountered.

Source: Madison Transportation Planning Board's CMP (2011), Table 11

Monitoring Plan

A performance based, outcome-oriented CMP must include a plan to monitor the transportation system and report on improvements to travel-time reliability.

Performance measurement is a continuous process. This is especially true for assessing impacts on reliability, where the basis is measuring variability over time. The CMP may include a monitoring plan that enumerates for each performance measure the agency that is responsible for data collection, analysis, and archiving; how often the measure will be updated; and how it will be reported.

Table 2 on Page 7 of the Madison (WI) Transportation Planning Board's CMP [15] demonstrates how this could be formulated.

Table 9: Example of a Performance Monitoring Plan from Madison, Wisconsin

Performance Monitoring Plan

Performance Measure	Data Type	Collector	Analyst	Archive Owner	Update Cycle
Freeway LOS	Freeway volume	WisDOT	MPO	MPO & WisDOT	Annually
Freeway Travel Time Index	Corridor or segment travel time	Floating car: MPO Automated: WisDOT	MPO	MPO & WisDOT	Floating car: 3 year cycle Automated: quarterly
Freeway congestion duration	Hourly traffic volume	WisDOT, City of Madison	City, MPO, WisDOT	City, MPO, WisDOT	Tri-annually on selected corridors
Freeway non-recurring delay	Crash records Service patrol records	Dane County Sheriff, TOPS lab Dane County Sheriff, STOC	WisDOT WisDOT	MPO, WisDOT MPO, WisDOT	Annually
Freeway Incident Index	Incident location, duration, lane closure	WisDOT, Dane County Sheriff	MPO	MPO, WisDOT	Annually

Source: Madison Transportation Planning Board's CMP (2011), Table 2

Problem Identification

This step of the CMP provides the MPO an opportunity to identify reliability problems related to non-recurring congestion, based on their adopted performance measures.

This example shows how reliability is incorporated into the problem identification stage of the process. This example is from the Durham-Chapel Hill-Carrboro Metropolitan Planning Organization, emphasis added.

Problem Identification

To identify the causes of the problem for the reported corridors or intersections, the results of the following analyses will be carefully reviewed:

Existing facility analysis (lane configuration, signal-timing plan, bus loading bay, bicycle/pedestrian facilities, surrounding land uses, and driveway density),
Capacity analysis (V/C ratio during a peak-hour and daily),
Intersection LOS analysis (control delay during a peak-hour),
Corridor analysis (intensity of travel time index during a peak-hour and daily),
Temporal and spatial extension of congestion (V/C ratio or travel time index during daily), and
Collision analysis (crash types and incident severity during last 5 years)

This comprehensive analysis results will help to find the problem causes and lead to the development of an improvement strategy.

V/C = Volume to capacity
LOS = Level of service

Source: Durham-Chapel Hill-Carrboro Metropolitan Planning Organization "Congestion Management Process: Procedures and Responsibilities Report", June 2011, p.31

Identification of Strategies

In this step, the MPO specifies the project, actions, and strategies it intends to undertake to improve reliability.

The following excerpt from page 48 of the Genesee Transportation Council (Rochester NY) CMP [16] is a list of strategies for improving freeway operations, which should lead to improved reliability.

2. Urban Freeways — Operations

2.A. Incident Management

Definition: Incident management involves the coordination of three stages: detection/verification; response/clearance; recovery/information. The aim of incident management should be to quickly and efficiently clear incident scenes without endangering first responders or the traveling public. This returns the roadway to normal operations sooner and reduces the likelihood of secondary incidents. Many incidents are vehicle disablements that can be quickly cleared.

Congestion Mitigation Impacts: Reduced incident-related delay; fewer secondary incidents.

2.B. Highway Information Systems

Definition: Communicate dynamic information regarding existing traffic conditions to travelers en-route on the transportation system. These capabilities include technologies such as Dynamic/Variable Message Signs (DMS/VMS), Highway Advisory Radio (HAR), and in-vehicle/handheld systems such as Geographic Positioning Systems (GPS) and personal travel assistants.

Congestion Mitigation Impacts: Reduced speeds of vehicles nearing queues (fewer secondary crashes); diversion to alternate routes/modes.

2.C. Ramp Metering

Definition: Ramp meters are modified traffic signals placed at the end of highway entrance ramps. This controls the flow of vehicles onto highways by breaking up platoons of vehicles attempting to enter the highway, thus streamlining the merge process. Delays may be incurred for ramp traffic, but mainline capacities are protected and overall operational efficiency is improved.

Congestion Mitigation Impacts: Increased freeway capacity; reduced short freeway trips; increased volume/capacity ratio on highways; decreased crash rate.

2.D. Highway Pricing Strategies

Definition: Levy fees for driving during peak travel times or under congested conditions. Place a surcharge on parking in congested areas. Use electronic toll collection systems to ease congestion at toll booths.

Congestion Mitigation Impacts: Diversion to alternate routes; mode switches; destination changes; increased trip chaining.

2.E. Road Work Zone Management

Definition: Manage road work zones to mitigate their impact on traffic. Limit work activities to off-peak travel hours; phase work activities on a daily, weekly, or seasonal basis to minimize traffic impacts; conduct a public awareness program in advance of road work; identify and promote alternate routes; promote ridesharing or transit use.

Congestion Mitigation Impacts: Improved throughput around road work zones; minimized vehicle delays and speed reductions; reduced crash rate.

Source: Genesee Transportation Council CMP (2013), Page 48

Implementation Strategies and Monitoring Strategy Effectiveness

The ultimate purpose of the CMP is to create a rational approach to mitigating congestion. The policy board can weigh the highest priority CMP projects and strategies against other needs when the MPO develops its transportation improvement program (TIP)

The following shows how reliability strategies can be implemented and monitored to assess effectiveness. This example is from the Durham-Chapel Hill-Carrboro MPO (emphasis added).

Chapter 8 - Implementing Strategies and Monitoring Strategy Effectiveness

The previously identified improvement strategies should be incorporated into the regional transportation plan and the TIP. The implementation processes of the defined strategies will be closely monitored if the improvements are adopted in the TIP or other program with the financial commitment. The implementation of the improvement strategies will be led by the operating agencies, and the progress should be reported to the MPO every month.

The implemented strategies will be monitored to assess their effectiveness. Monitoring techniques and schedules will be dependent on the type of improvement that is implemented, and the data availability. It may take years to assess the benefits of safety-type improvements that are intended to reduce crash rates, crash severity, or incidents. Conversely, the benefits of capacity improvements are relatively easy to measure and assess. Travel time reliability improvements will be monitored via the existing data collection methods within the region.

The benefits of the implemented strategies will be documented in the biannual report. For the improvements that may not be accurately measured in a two year time frame, results will be presented with a description of the limitations of monitoring. Capacity projects and other improvements that are implemented through non CMP methods will still be monitored to determine their benefits. Based upon the monitoring results, the learned facts will provide feedback for the CMP to verify and update the used performance measures, the applied data analysis techniques, and the considered strategies. If necessary, the CMP objectives and the CMP itself will be adjusted.

Source: Durham-Chapel Hill-Carrboro MPO

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