Traffic Monitoring Guide

Chapter 2 TRAFFIC MONITORING PROGRAM – BUSINESS PLANNING AND DESIGN

2.1 INTRODUCTION

This chapter addresses the high-level design of a traffic monitoring program and how data business planning can be used to support the design and development of the program at State highway agencies. It provides guidance on designing a traffic monitoring program and explains the importance of having such a program from three perspectives: statewide, regional/sub-area, and roadway facility/corridor-specific traffic monitoring. It also describes recommendations for a traffic program evaluation to be conducted by States every five years. More detail regarding guidance and examples of traffic monitoring programs are provided in Chapter 3 and the Appendices.

2.2 PROGRAM DESIGN

Many transportation agencies have recognized that traffic data programs support a growing variety of functions and critical decision processes within their agencies. The need for data and the benefits that result from the required data must be balanced against available and potential resources to implement an effective and efficient traffic monitoring program.

Therefore, in planning and designing a traffic monitoring program it is critical to consider one’s customer needs and the benefits that result from the timely delivery of quality traffic data for decision support. The customers of traffic data programs generally fall into the following categories:

• National Agencies – Such as FHWA for supporting national transportation policy development and in compiling national reports such as traffic volume trends or Highway Performance Monitoring Programs (HPMS), or the National Condition and Performance Report;
• State DOT Partners – Such as State operations, safety, bridges, planning, design, construction, maintenance, environmental, enforcement, and freight offices;
• Local Agencies – Local governments and metropolitan planning organizations (MPOs); and
• Public – Including public requests.

The components of traffic data programs include planning, design, calibration, collection, distribution, analysis, reporting, and maintenance. Uses of traffic data include project and resource allocation programming; performance reporting; operations and emergency evacuation; capacity and congestion analysis; traffic forecasts; project evaluation; pavement design; safety analyses; emissions analysis; cost allocation studies; estimating the economic benefits of highways; preparing vehicle size and weight enforcement plans; freight movement activities; pavement and bridge management systems; and signal warrants, air quality conformity analysis, etc.

The following table is a useful resource detailing some of the uses of traffic data collection that includes traffic counting, vehicle classification, vehicle weighing, and speed monitoring.

TABLE 2-1 EXAMPLES OF HIGHWAY TRAFFIC DATA USES

Highway Activity	Traffic Counting	Vehicle Classification	Vehicle Weighing	Speed Monitoring
Design	Highway geometry	Pavement design, bridge design	Pavement design, bridge design, and monitoring	Highway geometry
Engineering Economics	Benefit of highway improvements	Cost of vehicle operation	Benefit of truck climbing lane	Costs associated with congestion
Finance	Estimates of highway revenue and toll revenue	Highway cost allocation	Highway cost allocation	User travel time costs
Legislation	Selection of highway routes	Speed limits and oversize vehicle policy		Speed limits
Maintenance	Selecting the timing of maintenance, by lane volume for lane closure policies	Selection of maintenance activities	Pavement management, bridge management	Work zone safety measures
Operations	Signal timing, by lane volumes Traveler information emergency evaluation	Development of control strategies and speed by class Freight	Weight enforcement activities Freight	Setting speed limits and speed by class Traveler information
Planning	Location and design of highway systems	Forecasts of travel by vehicle type	Truck lanes Truck ramps Freight	Congestion measurement systems
Environmental Analysis	Air quality analysis, noise impact analysis	Forecasts of emissions by type of vehicle	Emissions by type of vehicle	Project-level analyses
Safety	Design of traffic control systems and accident rates	Safety conflicts due to vehicle mix and accident rates	Weight limits and regulations	Design of safety systems
Statistics	Average daily traffic	Travel by vehicle type	Average weight by vehicle class	85th percentile
Private Sector	Location of service areas Development planning	Marketing keyed to particular vehicle types	Trends in freight movement Truck lanes	Accessibility to service areas
Administration, Other	Performance measurement, resource allocation, emergency operations, asset management	Lane use Tax administration	Enforcement

The TMG is designed to provide guidance to States, MPOs and local agencies in establishing and maintaining a traffic monitoring program. Other national reference material includes the AASHTO Guidelines for Traffic Programs and the ASTM Loop Detector Handbook. Many States have developed their own statewide versions of traffic monitoring guidelines including Florida, California, and Texas (Appendix D, Case Study 1).

The following text describes the purpose and framework for establishing a traffic monitoring program. These programs are designed to collect traffic data and monitor travel within a defined geographic area for a State, region, or at the roadway-specific level. The types of data collected primarily consist of volume, classification, weight, and speed data. Many traffic programs are also adding bicycle and pedestrian counting. In the TMG, motorized programs include traditional traffic and non-motorized refers to bicycle and pedestrian counting programs. Chapter 4 is dedicated to guidance on bicycle and pedestrian counting.

2.2.1 STATEWIDE TRAFFIC MONITORING PROGRAM DESIGN

A traffic monitoring program is important from a statewide perspective to meet Federal and State requirements and is used to monitor travel primarily on State system roads. Traditionally, statewide traffic monitoring programs were designed to collect primarily three types of data: volume, classification, and weight. Speed data has now been included to address the need for data related to travel times and to determine the impact of speed on traveler safety. Each type of data can be used for many purposes, including tracking traffic volume trends on important roadway segments; providing input to traffic management and traveler information systems; determining truck travel patterns; providing input for safety and design studies along with roadway performance monitoring; and for providing data for programs such as the Highway Performance Monitoring System (HPMS). Traffic data reported to FHWA is used to apportion funding to States from the U.S. Highway Trust Fund. Proper support and funding of traffic counting programs is critical to ensure the State data collection remains up to date and is providing the best possible data.

The information obtained from statewide traffic monitoring programs is also the primary information resource for almost all general queries about road use in a State. Many users, both inside and outside of State highway agencies, periodically need basic traffic statistics, and those statistics should be readily available and comparable throughout the State. The statewide traffic monitoring program is responsible for collecting and providing that information. Requests for statewide data can range from how vehicle miles of travel are changing in order to compute carbon emissions to whether specific roads carry enough volume to warrant new retail construction activity. Having a strong statewide counting program allows an agency to answer a wide range of key policy and business questions confidently and effectively. Roadway agencies that cannot provide direct, timely, and accurate answers to these basic queries risk losing their credibility and subsequently the support of decision makers and the taxpaying public.

Traffic counts are fundamental to almost every task a highway agency performs and critical to a comprehensive performance measurement system. The timely delivery of high quality data can serve as a critical framework for effective decision making. The ability to describe how much traffic is using a road reflects positively on the agency’s ability to effectively perform its responsibilities and manage its budget. Consequently, collecting, summarizing, using, and reporting this data is a critical task for any roadway agency, delivering more relevant and cost effective data for operations, construction, and maintenance decisions and planning with benefits across the transportation system. Additional information with an example of the design of a statewide traffic monitoring program is found in Appendix D.

The measurement of traffic volumes and its composition (class, weight, speed) is one of the most basic functions of highway planning and management. Traffic volume counts are the most common measure of roadway use and count data is needed as input to nearly all traffic engineering analyses. While several traffic volume statistics are used in traffic analyses, of primary interest for the design of statewide traffic monitoring programs are annual average daily traffic (AADT) and average daily vehicle distance traveled (DVDT). Because DVDT is computed by multiplying the roadway segment AADT by the length of that segment, the primary goal of most traffic monitoring programs is to develop accurate AADT estimates, which can then be expanded to estimates of travel.

The recommended framework for a traffic monitoring program consists of two basic components:

Continuous Count Program (Volume, Speed, Classification, and Weight)

All highway agencies should have access to data collected from continuous counters. Agencies should work with each other to ensure that enough data is collected and shared to allow calculation of accurate adjustment factors needed to convert short-duration traffic counts into estimates of AADT. Chapter 3 in the TMG provides considerable guidance on how to structure continuous count programs, how to determine the appropriate number of counters for adjustment factor development, and how to apply those factors.

The continuous counts help the agency understand temporal (time-of-day, DOW, month-of-year and multi-year) changes in traffic volume, speed, class, and weight and allow development of the mechanism needed to convert short-duration counts into accurate estimates of annual conditions. Adjustments to short-duration count data are normally required to remove temporal bias from data used for AADT computation.

Short-Duration Count Program Design (Volume, Speed, Classification, and Weight)

Highway agencies perform short-duration counts for a variety of purposes including meeting Federal reporting needs (HPMS), supplying information for individual projects (pavement design, planning studies, etc.), and providing broad knowledge of roadway use. The portable short-duration counts also ensure geographic diversity and coverage. The short-duration counting program is most efficient if these various data collection efforts are coordinated so that one count program meets multiple needs. Examples of coordination include: sharing counting schedules with city/county/MPO staff; putting technology solutions in place that include access to software that encourages the integration/dissemination/conversion of schedules/data collected from city/county/MPO and State agencies; and establishing a data governance committee that crosses agency jurisdictions including national, State, county, city, and MPO boundaries.

The two types of short duration counts are described in the following sections.

Short-Duration Coverage Counts and Special Needs Counts

The coverage count subset covers the roadway system on a periodic basis to meet both point-specific and area needs, including the HPMS reporting requirements. The TMG recommends that the short-count data collection consist of a periodic comprehensive coverage program over the entire system on a maximum six-year cycle. The coverage plan includes counting the HPMS sample and full-extent sections on a shorter (maximum) three-year cycle to meet the national HPMS requirement.

The coverage program is supplemented with a special needs element where additional counts are performed as needed to meet other more specific data needs. The special needs program represents many different operations and may include the following:

• Pavement design counts performed to provide data for pavement design, maintenance, repair, rehabilitation, and reconstruction;
• Traffic operations counts performed to provide inputs to traffic control studies (e.g., the creation of new signal timing plans);
• Traffic counts for other special purpose studies; and
• Lane closure policies, corridor studies, inclement weather, and construction management.

The specific requirements (what is collected, when and where it must be collected) for these and other special needs studies vary from agency to agency. The ways in which agencies balance the benefits and costs of addressing these all-encompassing needs against their limited traffic counting budgets lead to the very different data collection programs that exist around the country.

Classification Data Needs

Vehicle classification data is a critical component of a well-designed traffic monitoring program because substantial amounts of classification data are needed to understand motorcycle, bus, and truck travel on highways. To address the need for classification data, the TMG recommends a coverage program structure for both volume and vehicle classification programs. More detail is provided in Chapter 3.

2.2.2 REGIONAL AND SUB-AREA TRAFFIC MONITORING DESIGN

A traffic monitoring program is used at the regional and sub-area level to address information needs on roads that are not met as part of a general statewide program. Traffic monitoring at this level is generally more detailed than the statewide program, and may include roads that are not part of the statewide program.

Regional or sub-area monitoring plans are generally designed to answer specific questions of regional importance. They often provide additional detail on traffic movements that cross-jurisdictional borders (e.g., they may provide data that are used to allocate State resources between jurisdictions within the region), or provide data needed to answer key scoping questions for upcoming regional projects. For example, urban areas often collect congestion and travel time reliability data. Similarly, geographic areas that depend on recreational traffic movements often collect data in different ways or times than would otherwise be collected for general State traffic monitoring purposes. Detailed regional traffic counts can be vital to maintaining or improving the economic vitality of communities that depend on recreational movements. Additional information with an example of the design of a regional traffic monitoring program is found in Appendix D, Case Study 4.

2.2.3 ROADWAY FACILITY SPECIFIC TRAFFIC MONITORING DESIGN

Facility-specific monitoring plans are the most detailed level of the three types of traffic monitoring programs. Roadway facility-level monitoring provides data needed at the project level. A minimum of four data items are typically produced as part of these monitoring efforts: AADT, K-Factor, D-Factor, and truck percentages. However, monitoring efforts may also collect data items that are needed for specific project purposes such as vehicle speed distributions and turning movements.

Facility-specific traffic monitoring programs are designed to provide the site-specific traffic statistics needed for roadway improvement and planning studies. They are also used to collect the detailed data needed to design, implement, and refine traffic operations plans (e.g., traffic signal timing or event planning). Well-designed facility monitoring plans are fundamental to the effective management and operation of heavily used roadways.

2.3 PROGRAM EVALUATION

It is in a DOT agency’s best interest to strategically conduct a comprehensive evaluation of their traffic monitoring program at a minimum of once every five years. This comprehensive evaluation should include all aspects of the program including equipment inventories, site selection procedures, data collection practices, validation, quality control, analyzing data, and data dissemination practices. A comprehensive travel monitoring program evaluation should provide an agency with a strategic business plan that documents program strengths and deficiencies with targeted recommendations for minimizing deficiencies and leveraging data program assets for a broad range of agency needs. A comprehensive program evaluation is recommended every five years because travel monitoring equipment and technology, as well as Federal regulations requiring travel monitoring data, can change over time, ultimately requiring travel monitoring program changes.

Conducting a program evaluation can benefit a DOT agency by saving the agency time, resources, and money by implementing newly recommended business practices that eliminate unnecessary or inefficient processes or data management practices. Examples include (but are not limited to) the following:

• Sharing of data with partner agencies and eliminating duplication of data collection efforts;
• Eliminating of travel monitoring sites by consolidating data sources that are overlapping within an agency;
• Implementing of automated software technologies to eliminate manual or electronic processing of data as well as eliminating inefficient or unnecessary business process steps;
• Purchasing and integrating private sector data to supplement existing data sources within the program;
• Upgrading site equipment to include cellular (preferred)/dial-up modems or establishing fiber network access eliminating the need for site visits to download data; and
• Integration of travel monitoring program data with Intelligent Transportation Systems (ITS) data eliminating duplication of efforts within an agency – this requires coordination and standardization of data collection efforts (time of collection 24 hours without gaps), resources, data export formats, etc.

Many agencies already rely on obtaining advice from partner Federal, State, and local agencies related to budgeting, monitoring equipment, resource allocations, etc. When conducting a comprehensive program evaluation a similar industry practice is advised.

Managing a travel monitoring program requires many different skills including budgeting; resource allocations; statistical analyses and quality evaluation of the travel monitoring program’s data. The travel monitoring program industry currently lacks the ability to evaluate and rank data programs based on a national standardized performance matrix. Although the Federal Highway Administration (FHWA) has the ability to evaluate continuous count programs by the number and quality of continuous count station data by State, currently there are no metrics for other travel monitoring program aspects such as short-duration counts programs, weigh-in-motion, etc. The remainder of this section describes the steps for conducting the program evaluation.

The program evaluation review should include the following elements.

FIGURE 2-1 STEPS FOR ESTABLISHING A CONTINUOUS DATA PROGRAM

Source: Federal Highway Administration.

FIGURE 2-2 TRAFFIC MONITORING PROGRAM BUSINESS PROCESS REVIEW STEPS

Source: Federal Highway Administration

This business process review should be updated annually to ensure the optimum use of resources with respect to stakeholder needs. States have embarked on business process reviews to document their processes, identify gaps, and improve their traffic monitoring programs. Good examples are provided in Appendix K for Georgia DOT and Colorado DOT.

Data Business Planning is an important component of any State DOT traffic monitoring program because it ensures that customer needs are met and the most efficient methods are deployed. It also provides accountability, transparency, and other strategic management benefits such as answering “what does your data program staff do?” Several States including Texas, Florida, Colorado, Virginia and Ohio have well-documented programs and can be used as references (see Appendices D, E, and K).

2.4COORDINATING COUNT PROGRAMS AND SHARING DATA

This section recommends best practices in coordinating count programs between State highway agencies and external agencies, and the methods used for sharing data.

Access to data collected from continuous counters is encouraged for all highway agencies. Considerable benefit can be obtained by sharing these data collection resources. Access to additional counts will provide data for quality assurance, filling of count gaps, saving money, and ease of reporting because all data can be integrated into one platform. On the other hand, the challenges to sharing data among agencies can be many, but are not insurmountable. For example, data may exist in different formats or be collected with different standards (e.g., 24-hour versus 48-hour counts). With carefully planned and implemented management strategies in place, (such as creating a data governance committee, implementing QA/QC data procedures, and having a scalable enterprise-wide data warehousing solution) an agency can not only overcome data sharing challenges, but benefit significantly through data sharing best practices.

Agencies should work together to reduce duplication in the number and location of permanent, continuous data collection devices. Agencies should share the data they collect (e.g., a State DOT could use monthly and DOW information collected at permanent sites operated by a county or city as part of developing adjustment factors for a specific urban area). A single count location can supply information for many purposes (e.g., permanent, continuous weigh-in-motion scales supply weight, classification, speed, and volume data). Opportunities to share data exist not only among agencies but also within agencies. Ensuring that planning, operations, maintenance, and construction groups share the data they collect can substantially increase the availability of traffic monitoring data and benefits derived, while reducing the overall cost of data collection.

A key source for urban traffic data is the traffic surveillance systems used for traffic management and control. The Intelligent Transportation System (ITS) program (see more information in Chapter 5) offers highway agencies the ability to collect continuous traffic monitoring data at high volume locations. Access to these data requires proactive efforts by the traffic monitoring groups, as archiving and analysis of surveillance data are traditionally less important to the operations groups that build, operate, and maintain these ITS systems. Without proactive efforts by the traffic monitoring groups, the benefits of ITS data can be lost because operations groups spend their scarce resources on operational improvements rather than on the archiving and analysis software needed to convert surveillance data into useful traffic statistics. Traffic monitoring assets can also supplement ITS assets and when configured appropriately can also provide critical information for operations.

Examples of best practices related to sharing traffic data can be found in Appendix D

2.5 TRAFFIC MONITORING CALIBRATION, PROCESSING, AND COMPLIANCE REVIEWS

This section describes the use of calibration procedures (explained more fully in Appendix F), the processing of data, and the use of compliance reviews to assess how well the State’s traffic monitoring program is performing in meeting MPO, State, and Federal requirements. This combination of tasks ensures that the traffic data collection equipment is working correctly, and that the data collected in the field is correctly processed to ensure that the summary statistics being reported accurately reflect the traffic conditions that are occurring on the roadway.

On-site and in-office calibration and tracking of site information should occur regularly (daily, monthly, and annually as needed). Having a robust traffic monitoring calibration program in place includes:

• Implementing software tools that help automate the process;
• Performing daily diligence activities such as business processes that ensure checking the quality of data as it is collected/processed/stored in the master (centralized or distributed) traffic database;
• Evaluating data using monthly trends and yearly trends to determine validity;
• Conducting field calibration;
• Collecting manual counts and comparing counts against portable equipment collected counts; and
• Performing manual and electronic calibration of classification, weigh-in-motion, volume, speed, and portable hardware annually.

Calibration includes performing a variety of tests on equipment to ensure that it functions as intended and correctly collects, processes, and reports the traffic data. The calibration process can identify both major errors (such as failed sensors) and minor errors (such as errors in site set-up, or the wrong classification algorithm installed on a shipment of devices) that can result in the collecting, processing, storing, and disseminating of inaccurate traffic statistics. The entire traffic monitoring program credibility is at stake when erroneous data is collected, processed, stored and disseminated. To avoid the risk of producing and disseminating erroneous data, traffic data programs should calibrate often.

Errors associated with calibration inaccuracies significantly increase the cost and decrease the usability of data from the entire traffic monitoring program.

However, once the data have been physically collected, more work remains to be done. To convert data into published statistical information, an agency must process (integrate, convert, calculate, QA/QC, store, manage, and provide access, etc.) the data consistently and correctly. Correct and consistent data processing ensures that AADT estimates produced from a simple axle counter can be accurately compared with AADT estimates collected using a sophisticated vehicle classifier. Consistent processes also ensure that agency credibility which allows an agency to easily defend their reported statistics and show through transparent audit processes that their data accurately reflect current traffic conditions. This allows States to pass Federal compliance reviews used to ensure that reported VMT statistics, a key variable used in funding allocation, are being accurately reported, and assures decision-makers the data deliverables are appropriate for critical decisions.

2.6 QUALITY ASSURANCE – STARTS WITH THE DATA QUALITY ACT (DQA) REQUIREMENTS

Data quality assurance processes are a critical component of any well-designed traffic monitoring program. The TMG recommends that each agency improve the quality of reported traffic data by establishing quality assurance processes for traffic data collection and processing. Each highway agency should have formal, documented rules and procedures for their quality control efforts.

The Data Quality Act (DQA) directs the Office of Management and Budget (OMB) to issue government-wide guidelines that provide policy and procedural guidance to Federal agencies for ensuring and maximizing the quality, objectivity, utility, and integrity of information (including statistical information) disseminated by Federal agencies.

A comprehensive and quality documented process will also assist in a smooth succession when there is turnover in staff.

2.7 DOCUMENTATION AND METADATA

Another critical factor of a well-designed traffic monitoring program is thorough and complete documentation. States are encouraged to maintain adequate documentation to support the decisions made and to allow future reexamination of those decisions as experience is gained in such areas as the factoring process. Documentation, such as the HPMS annual report which includes a requirement for reporting of metadata pertaining particularly to traffic and pavement data, is also recommended for any processes or methods used in data collection and analysis that may affect the outcome of the traffic data reported.

Metadata is documentation used to describe specific data items and datasets. HPMS recommends reporting of metadata that contains data that captures and explains variability in the collection and reporting of traffic (and pavement) data. For example, the traffic metadata may be used to describe if AADT values have been seasonally adjusted, if AADT values are directly (raw unadjusted data) from vehicle count data, or if AADT is adjusted by annual growth/change.

NCHRP Report 666: Target-Setting Methods and Data Management to Support Performance-Based Resource Allocation by Transportation Agencies also explains that it is becoming more common for documentation of data programs to be a shared responsibility between IT divisions and business units within the organization. The business units have a responsibility to document the business needs and benefits for the traffic programs so that executives internally, as well as external entities such as legislatures, are aware of the importance of continued funding and resource allocation to support these critical programs. Establishing structured documentation procedures includes having well defined change tracking mechanisms to ensure that the prioritization of requested system changes is in accordance with the primary goals and objectives of the agency (NCHRP 666, 2010).

All types of documentation that are used to support traffic monitoring programs become a significant part of the repository of information about the program. This important information can be used at the national level for modeling travel trends, conducting highway safety and weight studies, as well as supporting State needs and uses for the data. Appendix D contains an example case study from Texas that demonstrates the importance of documentation in supporting its statewide traffic monitoring program.