Traffic Monitoring Guide

Annual Average Daily Traffic

The total volume of vehicle traffic of a highway or road for a year divided by 365 days. It is meant to represent traffic on a typical day of

the year.

Annual Average Daily Bicycle Traffic

Annual Average Daily Bicycle Traffic identifies the volume of bike traffic for the average one day (24-hour period) during a data-reporting year at a specific location or specific segment of road or trail.

Annual Average Daily Motorcycle Traffic

Annual Average Daily Motorcycle Traffic identifies the volume of motorcycle traffic for the average one day (24-hour period) during a data-reporting year at a specific location

Annual Average Daily Micromobility

Traffic

Annual Average Daily Micromobility Traffic identifies the volume of bike, pedestrian, and other nonmotorized traffic for the average one

day (24-hour period) during a data-reporting year at a specific location.

Annual Average Daily Pedestrian Traffic

Annual Average Daily Pedestrian Traffic identifies the volume of pedestrians for the average one day (24-hour period) during a data-reporting year at a specific location.

Annual Average Daily Truck Traffic

The total volume of truck traffic on a highway segment for one year, divided by the number of days in the year. Computation of AADTT (by vehicle class) from a short-term count requires the application of one or more factors that account for differences in time-of-day, DOW, and monthly truck traffic patterns.

Annual Average Weekday Traffic

The estimate of typical traffic during a weekday (Monday through Friday) calculated from data measured at continuous monitoring sites.

Axle Correction Factors

Factors developed to adjust axle counts into vehicle counts. Axle correction factors are developed from classification counts by dividing the total number of vehicles counted by the total number of axles on these vehicles. However, the prevalence of data collection equipment that is dependent on pneumatic tubes that count axles rather than vehicles requires adjustments by applying an axle correction factor to represent vehicles. Equipment that detects vehicles directly (such as inductive loops or vehicle classification counters) does not require axle adjustment. In general, the higher the percentage of multi-axle vehicles on a road, the more error you will introduce into the data by not using

proper axle correction factors.

Active Infrared Sensor

Active infrared sensors use a signal transmitter on one side of the detection area and a receiver or target reflector on the other side. Active infrared sensors operate by sending a series of infrared pulses in a beam from a transmitter to a receiver. When the beam is broken for

a time interval, then an event or count is registered.

Average Daily Motorcycle Traffic

The total motorcycle volume during a given time interval (in whole or partial days), greater than one day and less than one year, divided by the number of days in that time interval. ADMCT is also known as raw

data and unadjusted or non-factored data.

Average Daily Traffic

The total volume during a given time interval (in whole or partial days), greater than one day and less than one year, divided by the number of days in that time interval. ADT is also known as raw data and

unadjusted or non-factored data.

Automatic Traffic Recorder Site

The location of an automated traffic recorder (permanent station) used for collecting traffic volume data; now use the term CCS.

Annual Vehicle Distance Traveled

Annual Vehicle Distance Traveled identifies the distance traveled by vehicles over a 1-year (365-day) period.

Axle Spacing

For each vehicle axle, the horizontal distance between the center of that axle and that of the preceding axle is the vehicle axle spacing

(ASTM E17.52, E1572-93).

Axle Weight

The weight (normal force) placed on the road by all wheels of one axle.

Blank-Fill

When the value in a field does not consume all the columns for the field, leading blanks are to be used starting at the left of the field. For example, if a field is five columns wide, and the data value is 250, then a blank-filled representation for this field is _ _ 250.

Classification Scheme

A classification scheme provides detailed information about how travelers are organized within a structured naming convention. For example, the most common vehicle classification scheme is a 13-bin structure, where 13 different groups of travelers are organized. There is an example of the 13-bin classification scheme in appendix A.

Continuous Count

A continuous count is a volume count derived from permanently installed counters for a period of 24 hours each day over 365 days

(except for leap year) for the data-reporting year.

Continuous Count Station

Permanent counting site that provides 24 hours a day and 7 days a week of data for either all days of the year or at least for a monthly (seasonal) collection. Different types of counters (vehicle volume

counter, speed, classifier, and WIM) could be installed at a CCS.

Continuous Data Program

Refers to the program management aspects of maintaining, storing, accessing, and reporting data from continuous counters within an overall travel monitoring program. In some States, this is referred to as Permanent Count Program. For the purposes of the TMG, the program will be referred to as the Continuous Data Program.

Count

Refers to how the data are collected to measure and record traffic characteristics such as vehicle volume, classification (by axle or length), speed, weight, lane occupancy, or a combination of these characteristics. These characteristics are defined in more detail in other

parts of the TMG.

Coverage Count

Special temporary count taken on a 24-hour to 7-day basis for a specific segment of road, usually associated with HPMS sections.

Database for Air Quality and Noise Analysis

A tool created by FHWA to combine traffic data (HPMS and TMAS) from existing data sources into a single database and process the combined data into properly formatted inputs to EPA's Motor Vehicle Emission Simulator (MOVES) model and FHWA's Traffic Noise Model Aide (TNMAide).

Daily Vehicle Distance Traveled

The DVDT is calculated by multiplying the section AADT by the section length (miles or km) to compute section-specific DVDT. (A roadway section or subsection is a State-owned or off-system roadway identified by an eight-digit code. Each roadway section is defined by a beginning and ending milepost in the Roadway Characteristics Inventory). These are then summed for an entire stratum to compute DVDT.

Daily Vehicle Miles Traveled

Indicates how many vehicles have traveled over the distance of a route, for a data-reporting year, when reported as an average day for a

given year. (DVMT = AADT X section length).

D-Factor (D)

The directional distribution factor. It is the proportion of traffic traveling in the peak direction during a selected hour, usually expressed as a percentage. For example, a road near the center of an urban area often has a D-factor near 50% (+/-2%) with traffic volumes equal for both directions.

Extent

Spatial coverage for which the data are to be reported: functional system, NHS, sample, paved, etc.

Freight Analysis Framework

The Freight Analysis Framework (FAF), produced through a partnership between the Bureau of Transportation Statistics (BTS) and FHWA, integrates data from a variety of sources to create a comprehensive picture of freight movement among States and major metropolitan areas by all modes of transportation.

Federal-Aid Highways

All NHS routes and other roads functionally classified as Interstate, Other Freeways and Expressways, Other Principal Arterials, Minor Arterials, Major Collectors, and Urban Minor Collectors.

Full Extent

A population comprising all sections of a functional system of public roads, which serves as a statistical universe for HPMS sampling and

census data collection.

Full Extent Data

Data that are collected in a census of a whole population, which for HPMS means data collected on all sections of a functional system of public roads.

Functional Systems

Functional systems result from the grouping of highways by the character of service they provide. The functional systems (classifications) designated by the States in accordance with 23 CFR 470 are used in the HPMS.

Gap

The distance between the back bumper of one vehicle and the start of the next vehicle.

Headway

The time between the front of one vehicle and the front of the next vehicle.

Inductance loop detector

Inductance loop detectors operate by circulating a low alternating electrical current through a formed wire coil embedded in the pavement. The alternating current creates an electromagnetic field above the formed wire coil (1/2 the field height corresponding to the shortest leg of the loop), and a conductive object (e.g., car, truck, and bike) passing through the electromagnetic field will disrupt the field by a measurable amount. If this disruption meets predetermined criteria, then detection occurs and an object is counted by a data logger or computer controller.

Intrusive Sensor

Traditionally, most vehicle detection sensors were placed on top of or in the pavement (e.g., road tubes versus inductive loops). These sensors are commonly referred to as "intrusive" sensors.

K-Factor (K)

The proportion of AADT occurring in the peak hour is referred to as the peak hour proportionality K-factor. It is the ratio of peak hour to AADT. It is used in design engineering for determining the peak loading on a roadway design that might have similar traffic volumes. For example, by applying the K-factor to a volume, a design engineer can estimate design hour volume. The K30 is the 30^th (K100 is the 100^th) highest hour divided by the AADT.

Lane Occupancy

The percentage of time a vehicle occupies the detection zone. This can be used to describe congested conditions.

Metadata

Describe how data are collected or converted for reporting; explain variations in data that do not warrant the establishment of a collection requirement (e.g., type of equipment used, sampling frequency).

Monthly Average Daily Traffic

This can be computed by adding the daily volumes during any given month, dividing by the number of days in the month, and weighting the number of specific days in the month with the associated weighting factor for those number of DOWs in the given month. For MADT, most of the calendar month of data should be included with a minimum of at least one time increment for each DOW. For a CCS site that operates 365 days per year without failure, the MADT can be computed by adding the daily volumes during any given month and dividing by the number of days in the month. The new FHWA AADT/MADT method is

recommended for all MADT calculations.

Monthly Average Weekday Daily Traffic

The MADT for Monday through Friday are summed and then divided by five, or values calculated using just the weekdays are used.

Monthly Average Weekend Daily Traffic

The MADT for Saturday and Sunday are summed and then divided by two, or values calculated using just the weekdays are used.

Micromobility Detector

A traffic counter specially configured to collect pedestrian and micromobility (bicycle, e-bike, scooter, hoverboard, etc.) travel volume counts on roads, trails, and sidewalks; also reports data on type of traveler (pedestrian, bicycle, scooter, etc.) using pre-programmed algorithms that classify micromobility devices based on speed, axle

spacing, and other distinguishing attributes.

Monthly (Seasonality) Factor

The monthly (seasonality) factor is used to correct for month-of-year bias in short term counts. Directions on how to create and apply monthly factors are provided in the general discussion of factoring in Chapter 3. Those procedures are recommended for the HPMS reporting, discussed further in Chapter 5. States may choose to select alternative monthly adjustment procedures if they have performed the analytical work necessary to document the applicability of their chosen procedure.

National Highway System

The NHS is a network of nationally significant highways approved by Congress in the National Highway System Designation Act of 1995 and redefined by MAP-21. It includes the Interstate System, other roads, and connectors to major intermodal terminals.

National Performance Management Research Data Set

A national data set of average travel times on the NHS for performance measures and management activities. This data set is also available to State DOTs and MPOs to use for their performance management activities.

Non-intrusive sensors

Non-intrusive sensors can be overhead-mounted sensors, under-the-roadway sensors, and side-fired sensors. Side-fired sensors have the advantage of being mounted beside the road. This makes them easy to

install, access, and maintain.

Occlusion

Occlusion is the traffic being obscured from the side-fired non-intrusive sensors by vehicles (and particularly trucks) traveling in the lanes closer to the sensor. Occlusion results in undercounting of total volume and can bias speed estimates if the traffic on the inside of the roadway is traveling at a different speed than traffic on the outside lanes.

Passive Infrared Sensor

Passive infrared sensors use a signal transmitter only on one side of the detection area and operate by identifying a changing heat differential in the detection area. If the heat differential and pattern meet pre-defined criteria, then a detection and/or count is registered.

Peak Hour Factor

The hourly volume during the maximum traffic volume hour of the day divided by 15-minute volume multiplied by four, a measure of traffic demand fluctuation within the peak hour. It represents one hour of data at the peak time.

Portable Traffic Recorder or Counter

A vehicle counter or classifier that is portable/mobile (can be moved to different locations) and not permanently installed in the infrastructure, including sensors placed across the road.

Sample Panel (HPMS)

A collection of designated roadway sections within a system of public roads that is stable over time and is used to estimate attributes for the entire system.

Speed

The velocity measurement by redundant sensors or attribute of the measured traveler; this provides the instantaneous velocity of the traveler. Most often reported to the whole unit of mile per hour or

kilometers per hour.

Short Term Count

Counts that are collected for less than a continuous basis. This allows the temporal data to be expanded to other areas. Consequently, these could be considered as supplying spatial data. Count taken on a

24-hour to 7-day basis for roadway segment-specific locations. These counts may be used in special studies.

System or Network Usage

System or Network Usage refers to activity data that provides information about the number of travelers at or along a facility over a time period. The collection of activity data is used for performance measures and data driven decision-making of transportation investments that can be justified by tangible benefits.

Traffic Counter

Any device that collects pedestrian, bicycle, micromobility devices, and vehicular characteristics data (such as volume, classification, speed, weight). A traffic counter is placed at specific locations to record the distribution and variation flow by hour of the day, day of the week, and/or month of the year. It may be used to collect data continuously

at a permanent site or at any location for shorter periods.

Table of Potential Samples

A collection of roadway sections spanning the public road network that provides the sampling frame for selection of the HPMS Sample Panel.

Travel Monitoring Analysis System

The FHWA-provided online software used by States, MPOs, and cities to submit traffic data for Federal purposes.

User Profile and Access Control System

Federal Highway Administration's access control for information systems. The UPACS has two major functions: it provides users with a menu of systems that they have access to and provides authorized personnel a mechanism for granting such access. The UPACS provides access control for FHWA's applications through system-generated user IDs and user-supplied passwords and PINs, in combination with individual access profiles created for users by system owners.

Vehicle

Vehicles include one powered unit and may include one or more unpowered full-trailer or semi-trailer units (ASTM E17.52). Assembly of one or more units coupled for travel on a highway.

Vehicle Axle

The vehicle axle is the axis oriented transversely to the nominal direction of vehicle motion and extending the full width of the vehicle about which the wheel(s) at both ends rotate (ASTM E17.52, E1318-

17).

Vehicle Axle Spacing

For each vehicle axle, the horizontal distance between the center of that axle and that of the preceding axle.

Vehicle Class

The FHWA vehicle typology separates vehicles into categories, or classes, depending on whether they carry passengers or commodities. There are 13-vehicle classes identified by FHWA.

Vehicle Count

The activity of measuring and recording traffic characteristics such as vehicle volume, classification, speed, weight, or a combination of these

characteristics.

Vehicle Distance Traveled

The distance traveled by all vehicles for a given period, usually measured in miles (or metric in km) and reported as vehicle miles traveled (VMT) for a geographic region. There is a relationship between VDT and VMT, although each is distinctly different. While VDT is measuring a distance traveled, VMT is counting the number of vehicles traveled over a distance. Depending upon the formulas used, these numbers may be the same.

Vehicle Length

This refers to the overall length of a vehicle measured from the front bumper to the rear bumper including permanent equipment that may extend beyond the rear bumper such as that used to improve

aerodynamic performance.

Vehicle Occupancy

Number of persons inside a vehicle.

Vehicle Miles Traveled

Vehicle Miles Traveled indicates how many vehicles have traveled over the distance of a route, for a data-reporting year, when reported as Annual VMT (VMT = DVMT x 365). Indicates how many vehicles have traveled over the distance of a route or functional classification or geographic area in one day. VMT is calculated by multiplying the AADT value for each section of road by the section length (in miles) and summing all sections to obtain VMT for a complete route. VMT is not the same as daily vehicle distance traveled (DVDT), which measures the distance traveled by vehicles in a day, not how many (VMT) vehicles traveled over a given distance in a day. Depending upon the formulas used, these numbers may be the same.

Weigh in Motion

A measure of the vertical forces (normal) applied by axles to sensors in the roadway. This is used to measure the weight carried by vehicles

(trucks) to determine the appropriate pavement design.

Weigh in Motion System

A device that measures the dynamic tire forces of a moving vehicle to estimate the wheel, axle loads, and/or gross vehicle weight of the static vehicle. WIM systems also collect information about traffic and truck volume, speeds, vehicle classification, and axle spacing.

Zero-Fill

When the value in a field does not consume all the columns for the field, leading zeros are to be used starting at the left of the field. For example, if a field is five columns wide, and the data value is 250, then a zero-filled representation for this field is 00250.