FHWA-WFL/TD-10-002 2010

Traffic Monitoring:

A Guidebook

Federal Highway Administration 

U.S. Department Of Transportation
Technical Report Documentation Page

1. Report No.

 FHWA-WFL/TD-10-002

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Traffic Monitoring A Guidebook

5. Report Date

 July 2010

6. Performing Organization Code

7. Author(s)

Shawn Turner, P.E., Texas Transportation Institute; Jodi Carson, Ph.D., 

P.E., Texas Transportation Institute; L.J. Wilkinson, Chaparral Systems, 

Inc.; Kathy Travis, Chaparral Systems, Inc. Carol Zimmerman, Battelle

8. Performing Organization Report No.

9. Performing Organization Name and Address

Battelle Memorial Institute

505 King Ave.

Columbus, OH 43201

Texas Transportation Institute

Texas A&M University

College Station, TX 77843

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH71-07-D-00009, T-08-002

12. Sponsoring Agency Name and Address

 Federal Highway Administration

 Western Federal Lands Highway Division

 610 East 5th St.

 Vancouver, WA 98661

13. Type of Report and Period Covered

Final Report

2009-2010

14. Sponsoring Agency Code

 HFL-17

15. Supplementary Notes

 COTR: Amit Armstrong, Ph. D., P.E. 

This project was funded under the FHWA Federal Lands Highway Technology Deployment Initiatives and 

Partnership Program (TDIPP) and Coordinated Technology Deployment Program (CTIP). 

16. Abstract

Traffic Monitoring: A Guidebook discusses different approaches to traffic monitoring and helping decisions to be 

made are based on the quality of the traffic data being collected and how well that traffic data reflects the actual 

events that are occurring. This guidebook should aid the user in developing a basic understanding of traffic data 

collection principles and procedures. This guidebook will provide an overview of traffic monitoring through 

simple descriptions which explain the various basic concepts related to a successful traffic monitoring program. 

Furthermore, this document investigates some of the challenges associated with a traffic monitoring program 

including variability in traffic, adjustment factors, and strategies for assisting with under-funded programs. This 

guidebook does not attempt to cover every aspect and detail of traffic monitoring but provides a starting point 

that leads the user to a successful traffic monitoring program.

17. Key Words

TRAFFIC MONITORING, GUIDEBOOK, DATA 

COLLECTION, UNDER-FUNDED PROGRAMS

18. Distribution Statement

 No restriction. This document is available to the 

 public from the sponsoring agency at the website 

 http://www.wfl.fhwa.dot.gov/td/.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

44

22. Price

0

 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
Traffic Monitoring:

A Guidebook

Technology Deployment Program 

Western Federal Lands Highway Division 

Federal Highway Administration 

610 East 5th Street 

Vancouver, WA 98661

Technology Deployment Report Report Number FHWA-WFL/TD-10-002
SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol 

LENGTH in inches 25.4 millimeters mm 

ft feet 0.305 meters m

yd yards 0.914 meters m

mi miles 1.61 kilometers km

AREA in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2

ac acres 0.405 hectares ha 

mi2 square miles 2.59 square kilometers km2

VOLUME

fl oz fluid ounces 29.57 milliliters mL 

gal gallons 3.785 liters L

ft3 cubic feet 0.028 cubic meters m3

yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS

oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg 

T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")

TEMPERATURE (exact degrees) °F Fahrenheit 5 (F-32)/9 Celsius °C

or (F-32)/1.8

ILLUMINATION fc foot-candles 10.76 lux lx 

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N

lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH mm millimeters 0.039 inches in 

m meters 3.28 feet ft

m meters 1.09 yards yd 

km kilometers 0.621 miles mi 

AREA mm2 square millimeters 0.0016 square inches in2

m2 square meters 10.764 square feet ft2

m2 square meters 1.195 square yards yd2

ha hectares 2.47 acres ac 

km2 square kilometers 0.386 square miles mi2

VOLUME

mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft3

m3 cubic meters 1.307 cubic yards yd3

MASS

g grams 0.035 ounces oz 

kg kilograms 2.202 pounds lb

Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T 

TEMPERATURE (exact degrees)

°C Celsius 1.8C+32 Fahrenheit °F

ILLUMINATION

lx lux 0.0929 foot-candles fc 

cd/m2 candela/m2 0.2919 foot-Lamberts fl 

FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf 

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)
TABLE OF CONTENTS

1 INTRODUCTION

3 TRAFFIC MONITORING BASICS

4	 Who Needs Traffic Monitoring?

4	 What Is Traffic Monitoring?

5	 Where Is Traffic Monitoring Needed?

6	 When Is Traffic Monitoring Performed?

7	 Why Is Traffic Monitoring Performed?

8	 How Is Traffic Monitoring Performed?

9 TRAFFIC MONITORING 101

10	 What Does Traffic Monitoring Do for Me?

10	 What Resources Are Available?

11	 What Are the Types of Traffic Monitoring?

15 TRAFFIC MONITORING EQUIPMENT CAPABILITIES & LIMITATIONS

16 Manual Recording –Tally, Mechanical, Electronic

16 Accumulative Count Recorder

17	 Automated Traffic Recorder

17	 Automated Vehicle Classification Recorder

18 Weigh-in-Motion Recorder

18 Other Devices

19 SUCCESSFUL TRAFFIC MONITORING

20 Study Plan

21 Quality Control/Quality Assurance

23 Data Analysis, Summarization, & Reporting

29 Data Storage

31 STRATEGIES FOR UNDER-FUNDED PROGRAMS

37 LIST OF RESOURCES FOR ASSISTANCE 

The collection of traffic data plays a vital role in the decision

making process of the agency responsible for utilizing this

information. The decisions to be made are based on the quality

of the traffic data being collected and how well that traffic data

reflects the actual events that are occurring. This guidebook

should aid the user in developing a basic understanding of

traffic data collection principles and procedures and should

assist in the development of a successful traffic monitoring

program.

This guidebook will provide an overview of traffic monitoring

through simple descriptions which explain the various basic 

concepts related to a successful traffic monitoring program. 

The intent of this guidebook is to consolidate and simplify

technical and highly detailed traffic monitoring information

into a document that can be used as a first step or introduction

toward understanding traffic monitoring and the traffic

data collection process. Examples of the various traffic

monitoring types are described and summarized, along with 

a description of traffic monitoring equipment capabilities and

limitations. Furthermore, this document investigates some of

the challenges associated with a traffic monitoring program

including variability in traffic, adjustment factors, and strategies

for assisting with under-funded programs.

A successful traffic monitoring program begins with a plan that

includes a set of goals as outlined by an agency. To properly

attain these goals, quality control and assurance related

to personnel, equipment used, and data collected must be

considered. Only then can decisions be decided upon that

determine an appropriate course of action.

This guidebook does not attempt to cover every aspect and 

detail of traffic monitoring. Instead, this document provides a

starting point that leads the user to the locations of relevant

and more detailed information to assist in the establishment of

a successful traffic monitoring program.

INTRODUCTION
2
TRAFFIC MONITORING BASICS
4

Who Needs Traffic Monitoring?

Traffic monitoring is used by various federal, state, and local

governmental agencies, as well as private businesses which 

require information pertaining to travel patterns in their

respective regions. Federal agencies, such as the Federal

Highway Administration (FHWA) for example, require states to

collect data used to estimate total vehicle miles of travel (VMT)

in order to determine the apportionment of Federal-Aid funds. 

States and local government agencies will typically collect 

additional data that is used to determine pavement design, 

planning of future roadways, air quality, and maintenance

needs.

What Is Traffic Monitoring?

Traffic monitoring is the collection of information to describe

the use and performance of the roadway system based on the

following:

Traffic volumes – number of vehicles;

Vehicle classification (VC) – type of vehicle (e.g., car,

motorcycle, truck, etc.);

Vehicle occupancy – number of riders in a vehicle;

Truck weight volumes – number of heavy vehicles by

weight classification;

Pedestrian volumes – number of people walking; and

Bicycle volumes – number of bicycle riders.

Traffic Monitoring carried out to collect data on the number

of vehicles and/or pedestrians that pass a point on a roadway

facility during a specified time period. This same collected data

may also be put into categories, for example:

Vehicle occupancy rates (number of passengers

divided by number of vehicles);

Directional movement of vehicles (into or out of park

facility); and

Pedestrian age.
5

Where Is Traffic Monitoring Needed?

Traffic monitoring is needed in various settings and locations

depending on the use for the information that is collected.

For example, traffic monitoring can be performed on the

following:

Highways/Freeways

To determine the planning of highway activities;

To measure the current traffic demand; and

To evaluate existing traffic flow.

Arterial/Local Roads

To determine intersection improvements;

To change a speed limit on a particular road; and

To develop parking regulations.

Parking Areas

To determine the need for additional access locations;

To determine the location of pedestrian crosswalks,

Parks and Recreational Areas;

To determine the variability in usage of park roads;

To assist in developing schedules due to change in 

facility usage; and

To optimize traffic routing.
6

When Is Traffic Monitoring Performed?

Traffic monitoring is measured at various increments of time

depending on the intended use of the collected information. 

The choice of time periods can vary from as little as 5 minutes

to as much as a year and are derived from the following:

Time-of-Day

Minute intervals – 5, 15, and 30 minute intervals are common;

Peak hour volume (PHV) – highest traffic volume in a

consecutive 60 minutes;

Peakperiod–highesttrafficvolumeinaconsecutive180minutes;

Average daily traffic (ADT) – average of 24 hour counts

collected over a number of days greater than one but

less than a year;

Average annual daily traffic (AADT) – average of 24

hour counts collected every day in the year; and

Off-peak hours – traffic volumes not within the peak

period hours of a day.

Day-of-week

Weekday (Monday through Friday); and

Weekend (Saturday and Sunday).

Seasonal

Winter, spring, summer, fall.

Holidays

July 4, Labor Day, Memorial Day, etc.

Spring break, Thanksgiving break, etc.

Note: This information may be collected over the entire period of time

or a “sample” that represents the specific time period. “Sampling”

requires specific guidelines that should be followed to ensure accurate

collection of traffic information.
7

Why Is Traffic Monitoring Performed?

Traffic monitoring is performed in order to provide the

factual information needed to make proper assessments

and appropriate decisions related to travel patterns. Traffic

monitoring assists in the following types of decisions and

examples of applications:

Planning Decisions

To determine if a traffic signal is needed at an intersection;

To determine traffic control devices needed, such as

speed limit signs; and

To determine the functional classification of a roadway

to reflect principal use.

Design Decisions

To determine the number of lanes needed on a roadway;

To determine the load weight of a bridge to be built; and

To determine where improvements are needed.

Construction Decisions

To determine lane closures to minimize travel impacts; and

To determine routing alternatives around closed roadways.

Operational Decisions

To determine the signal phasing at an intersection;

To determine maintenance schedules for pavement

patching and repair; and

To evaluate air quality conditions.
8

How Is Traffic Monitoring Performed?

Traffic monitoring is performed using one of the following

available techniques based upon the length of the sampling

period. The available techniques include manual counting and

mechanical or automated counting which utilizes specialized 

equipment to collect the traffic information.

Manual Counting

Trained observer at each location

Short sampling period (less than 10 hours of data at any location)

Lower cost to perform

Less effort to implement

Equipment needs

Tally sheets

Mechanical or electronic count boards

Watch or stopwatch

Automated Counting

Automatic data collection equipment at each location

Longer sampling period (24 hours a day)

Higher cost to perform

More effort to implement due to equipment setup and retrieval

Equipment needs

Portable counters (24 hours a day, up to several weeks)

Sensor detectors include pneumatic tubes, piezoelectric 

strips, tape switches, and temporary induction loop 

detectors.

Permanent counters (24 hours a day, 365 days a year) 

Sensor detectors include induction loop detectors, bending 

plates, radar, microwave, and video imaging.
TRAFFIC MONITORING 101
10

What Does Traffic Monitoring Do for Me?

Traffic monitoring can provide travel related information

to anyone needing to make informed decisions based on

travel pattern information. The information obtained from

the collection of traffic data can assist in finding solutions to

transportation related problems once the extent and magnitude 

of that problem has been identified. Traffic monitoring can also

be used to determine improvements to various transportation 

facilities based on the collection of accurate information in

order to present a clear and objective description of how a

facility operates.

What Resources Are Available?

There are multiple resources available to assist in the 

development of a useful and successful traffic monitoring

program. Most of these resources were developed by

engineering and transportation professionals to assist in the

design, construction, and operation of the highway system. 

These same strategies can be applied to most instances where 

traffic related information is being collected. Several of the

most informative resources pertaining to traffic monitoring

guidance include the following web sites and/or publications:

Federal Highway Administration

Travel Monitoring. Policy information web page.

http://www.fhwa.dot.gov/policy/ohpi/travel/index.cfm

Traffic Monitoring Guide. FHWA-PL-01-021. 

http://www.fhwa.dot.gov/ohim/tmguide/index.htm

Traffic Detector Handbook: Third Edition. FHWA-HRT-06-108. 

http://www.tfhrc.gov/its/pubs/06108/index.htm

Highway Performance Monitoring System Field Manual for the Continuing

Analytical and Statistical Database. 

http://www.fhwa.dot.gov/ohim/hpmsmanl/hpms.cfm

Institute of Transportation Engineers

Manual of Transportation Engineering, 1994. 

Traffic Engineering Handbook, 4th Edition, 1992
11

What Are the Types of Traffic Monitoring?

There are several types of traffic monitoring alternatives

that can be carried out depending on the anticipated use of

the data to be collected. These types of alternatives include

vehicle volume counts which range from short term counts

to continuous counts, vehicle classification and occupancy

counts, truck weight counts, pedestrian counts, bicycle counts, 

and others that may be determined for a specific need. These

different counts will be discussed in the following sections.

Vehicle Volume Counts

Vehicle volume counts can provide a vast amount of information

which can assist in the decision making processes related to a 

highway or a system of highways. The data obtained provides

an estimate of the number of vehicles traveling a section of

highway over a specified period of time. Typically vehicle

volume counts will be in the range from short term counts to

long term continuous counts.

Short Term Counts at a Large Number of Locations

Short term counts are vehicle volume counts that are 

performed for intervals less than an hour (e.g., 5, 15, 30

minutes). It is not feasible to collect continuous data on all

roadways due to the cost involved. Short term volume counts

allow for a larger number of locations to be surveyed given

that the counting equipment is not monopolized by just a

few locations. Short term volume counts are typically used

to determine peak volume characteristics or to estimate 

annual traffic characteristics. Short term counts are typically

performed manually by observation or with portable automatic

counting equipment.

Continuous Counts at Select Locations

Continuous counts are vehicle volume counts that are 

performed for longer intervals (e.g., daily, weekly, and

seasonally). These counts are carried out on a continuous basis

utilizing automatic counting equipment and are sometimes

referred to as permanent count stations. Continuous volume

counts allow for a fewer number of locations to be surveyed

since the counting equipment is generally permanent and

is continuously operating at a limited number of locations. 

Continuous volume counts are typically used to determine 

fluctuations in weekly/seasonal traffic or to determine growth

rates of traffic.
12

The chart above summarizes the range of vehicle volume counts 

available and the respective purpose and use of each. 

Vehicle Classification/Occupancy Counts

Vehicle classification counts are counts that determine the type of

vehicle at a count location and are useful in determining seasonal

variations. These counts can be performed manually through

classifying the vehicle type by visual observation or by automatic

counting equipment that measures the length of a vehicle or

that measures the number of axles on a vehicle, depending

TYPES OF VEHICLE VOLUME COUNTS

SHORT TERM 

COUNTS 

PEAK-HOUR 

COUNTS

24-HOUR 

COUNTS

CONTINUOUS 

COUNTS

Analyze maximum 

rates of flow and

variation within peak 

hours

Determine 

deficiencies in

capacity 

Measure present 

demand for

service 

Determine 

fluctuations of

daily/weekly/

seasonal flow

Determine capacity 

limitations in urban 

areas

Aid in geometric 

design

Evaluate present 

traffic conditions

(e.g., signals)

Determine annual 

growth rate of

traffic

Determine 

characteristics of

peak volumes

Develop traffic

operation 

programs

Aid in highway 

planning

Determine varying 

demand for facility

Determine 

signal phasing at 

intersections

Validate travel 

models

Determine freeway

operations

PURPOSE AND USE

Source

North Central Texas Council of Governments

NPS CLASS FHWA CLASS

Motorcycles Class 1: Motorcycles

Passenger Cars Class 2: Passenger Cars

Recreational Vehicles Not Applicable 

Vehicles/RV pulling 

Trailer

Not Applicable

Transit/Shuttle Bus Class 4: Buses

Tour Buses Class 4: Buses

Light-Duty Trucks Class 3: Other two-axle, four-tire single unit vehicles

Class 5: Three-axle, six-tire, single-unit trucks

Heavy-Duty Trucks Class 6: Three-axle single-unit trucks

Class 7: Four or more axle single-unit trucks

Class 8: Four or fewer axle single-trailer trucks

Class 9: Five-axle single-trailer trucks

Class 10: Six or more axle single-trailer trucks

Class 11: Five or fewer axle multi-trailer trucks

Class 12: Six-axle multi-trailer trucks

Class 13: Seven or more axle multi-trailer trucks
13

on the type of sensor used. Vehicles are typically classified

into 13 vehicle classification categories as defined by Federal

Highway Administration (FHWA). However, vehicle classification

categories can be changed to accommodate other reporting 

needs, such as in parks and recreational areas where vehicle 

types may significantly differ from customary roadway usage. 

Vehicle occupancy counts

Vehicle occupancy counts are counts that determine the 

number of people in each vehicle at a count location and help

in determining travel modes and person movement within 

a region. These counts are usually performed manually by

personnel monitoring from the roadside. It is customary to

concurrently determine the vehicle classification and the

number of people in each respective vehicle while conducting

vehicle occupancy counts.

Truck Weight Counts

Truck weight counts are counts that determine vehicle 

weight loads and are useful in determining where heavy

loaded vehicles are traveling. These counts are performed

by automated equipment known as weigh-in-motion (WIM)

detectors. Sites chosen for this type of detector generally

reveal directional rutting in pavements; increased truck traffic

and/or high proportion of trucks; proximity to special truck

traffic generators; and seasonal influences of heavy loads (11).

Pedestrian Counts

Volume counts of pedestrians are made at locations such as

sidewalks, cross walks, and transit stations. The counts are

performed manually and are usually taken at these locations

when the evaluation of existing or proposed pedestrian facilities

is being considered. Pedestrian activity can be a major

component in the safety, design, and operation of sidewalks,

bridges, and underpasses.

Bicycle Counts

Volume counts of bicycles are made at locations with high

bicycle activity such as parks and recreational areas. The

counts are performed manually and are usually taken along trail

sections, bicycle lanes, or at bicycle staging locations. These

counts assist in determining the impacts bicycles have when 

interacting with other modes of travel, such as at intersections,

and in planning for future amenities related to bicycling.
14
TRAFFIC MONITORING 

EQUIPMENT CAPABILITIES 

& LIMITATIONS
16

Manual Recording –

Tally, Mechanical, Electronic

The basic form of a manual count involves personnel recording

information on a field sheet using a tally mark. It can

include data related to a vehicle passing a particular point, 

making a particular turning movement at an intersection, the 

classification type of a vehicle, or the number of pedestrians

utilizing a cross-walk. Tally marks should only be used for very

low volume locations, but they are a relatively inexpensive form

of counting.

Mechanical board counters may also be used for manual counts. 

This device is referred to as a multi-denominator tally and

mechanically records a count from the push of a button. This

device allows a person to count a higher volume location and 

typically can accommodate up to eight different categories. 

At predetermined time intervals, the cumulative information

is manually recorded by personnel on a field sheet. The

information can then be put into a spreadsheet for analysis

purposes. Collecting more than eight categories will involve the

use of more personnel to obtain the data.

Electronic board counters are similar in operation to mechanical 

board counters. However, the electronic board counter has

internal memory and will automatically store the collected 

information at desired time intervals. Upon completion of a

count, the data can be downloaded to a computer for analysis

purposes. The electronic Board counter is supplied with a

manufacturer program that allows for easy transfer and output

of the field data.

Accumulative Count Recorder

Accumulative count recorders (ACRs) are automatic counters 

that can be set up at a location and count continuously for

short periods of time (short term counts) up to several weeks. 

These devices utilize temporary sensors such as piezoelectric 

strips, tape switches, temporary induction loop detectors, or 

pneumatic tubes placed in the roadway. These sensors can

easily be positioned for counting and then retrieved for future

use at other locations. The most commonly used sensor for

an ACR is the pneumatic tube or “road tube.” The ACR is easy

and quick to install at locations and is relatively inexpensive

to operate. However, the road tube sensors will degrade over

time, are not as accurate for speeds less than 10 mile per hour

(mph), and are less accurate when recording on multiple lanes 

at one time.
17

Automated Traffic Recorder

Automated traffic recorders (ATRs) are automatic vehicle

counters that operate for longer periods of time and are set

up for more permanent function (continuous counts). These

devices utilize permanent sensors, such as induction loop 

detectors, which are installed directly into each lane of

pavement at a count location. An inductive-loop detector

senses the presence of a metal object by inducing currents in

the object. The ATR sensors tend not to degrade as rapidly as

the ACR temporary sensors. The automated traffic recorder

produces accurate data and works well where vehicle volumes 

are high. The data is often used to analyze travel trends at a

particular location, as well as to adjust short term count data

into estimates of annual, design, or average conditions (2).

Power and a communication link must be available at each 

location to allow for the continuous operation of the ATR.

Automated Vehicle Classification Recorder

Truck and recreational vehicle traffic often generates different

seasonal or day-of-week trends than do total volumes, which are

likely dictated by automobile traffic trends. Automated vehicle

classification (AVC) recorders can record the type of vehicle

based on a defined set of length or axle parameters. These

devices utilize permanent sensors (such as a set of induction

loop detectors in each lane) that monitor each lane of travel at

a count location. Classification is typically separated by lane,

direction, and sorted into the standardized FHWA 13-category 

classification scheme; however, most devices allow for sorting

up to 14 user-defined classifications. Classification data can be

easily converted to vehicle volume counts when needed. While

these devices perform best at locations with speeds around

45 mph, they do not function well for locations where traffic

is moving too fast or too slow due to miscounts. Power and a

communication link must be available at each location to allow 

for the continuous operation of the AVC recorder.
18

Weigh-in-Motion Recorder

Weigh-in-motion (WIM) recorders are devices that can 

determine the weight of a moving vehicle, in addition to

recording vehicle classification and volume. These devices

utilize permanent sensors (such as bending plates) or 

temporary sensors (such as piezoelectric strips) that monitor 

each lane of travel at a count location. WIM recorders are

highly accurate, typically within 10 percent of gross vehicle

weight (GVW). While these devices provide the most accurate

travel information, they also require greater investment for

equipment, installation, and site preparation, in addition to

greater maintenance needs. Power and a communication link

must be available at each location to allow for the continuous

operation of the WIM recorder.

Other Devices

There exist other types of sensors for automated counting

equipment not listed in the previous sections. These other

types of sensors are generally more expensive than the ones

listed above and typically require power and a communication

link at each location. Video imaging and active infrared

detectors utilize optical data capturing to perform vehicle

classification or vehicle turning movements at intersections. 

Unfortunately, these devices perform badly in poor weather

conditions and in high density locations due to occlusion (high 

profile vehicles obstructing the detector’s line-of-site of other

vehicles). Acoustic detectors are devices which utilize sound

waves to count vehicles, but perform poorly in echo-filled

environments. Remote traffic microwave sensors (RTMSs) are

miniature radar devices which utilize low-power microwave 

signals to detect vehicle classifications. The microwave

sensor is not affected by poor weather and does not have

issues related to occlusion. Finally, cellular and satellite

communications equipment is being utilized to provide vehicle

tracking information and could be useful in remote areas, but

this technology is still being developed.
SUCCESSFUL TRAFFIC MONITORING
20

Study Plan

A successful traffic monitoring program includes a plan which

outlines and provides details of the objectives that determine

a successful outcome. A good plan will help to keep costs low

and improve the quality of the collected traffic information

that supports the decision-making process. For example, if

the traffic volume is expected to be low on a roadway, then

a manual count performed periodically may be a simple

solution as opposed to the cost, installation, and maintenance 

associated with an automatic counter. A good study plan

should include an inventory of existing data, a field site

visit to potential count locations, and a defined set of goals. 

Detailing this information will assist in determining personnel

and equipment needs and help define data analysis and data

storage requirements in a cost-effective manner.

Existing Inventory

An agency can avoid unnecessary expenditure of money and

time through a greater understanding of the traffic data that is

currently available. Improved communication and coordination

within an agency and with other agencies can help minimize 

the amount of data that needs to be collected. Other agencies,

especially state governmental agencies, collect large amounts 

of traffic data throughout their respective jurisdiction. Data

collected on nearby state highways could be used to assist 

in determining patterns that may exist near potential traffic

monitoring sites or to develop adjustment factors that could be

used to approximate traffic conditions near potential sites.

Field Site Visit

A potential site for traffic monitoring requires an on-site field

visit to verify existing conditions and determine any available

infrastructure. The field site visit is used to determine if a

potential site is suitable for collecting traffic information, the

type of data collection to be performed (manual or automatic),

and all related characteristics needed to acquire good traffic

data. For instance, an unobstructed view of the roadway is

an important characteristic for conducting successful manual

counts. For automatic counts, it is important to determine

the traffic mix (including the number and type of trucks),

geometrics of the roadway (number of lanes, lane widths,

curvature of roadway, etc.), the pavement condition (is rutting

evident) which could affect the operation of a road tube, and

the power and data communication capabilities. 
21

Determination of Goals

A traffic monitoring program requires a set of goals that will

help accomplish the desired outcome. For one agency, that

goal may be to determine the total traffic on multiple roads

year to year, while another agency may be more interested in 

determining the type of vehicles that are using one particular

section of roadway. Each agency needs to determine the

type and amount of data to collect that will best support the

decisions to be made to ensure a successful outcome. Upon

determining the type and amount of data to be collected,

an agency can then decide the best methodology to collect 

the data and the types of equipment that will be needed to

accomplish this task, which should include the consideration of

personnel, cost, and budget issues.

Quality Control/Quality Assurance

The objective of a traffic monitoring program is to provide

good quality traffic information to support the future decisions

of an agency. The information obtained from the traffic

monitoring program is only as good as the quality assurance of

the personnel, the equipment, and the traffic count data. The

documenting of methodology and procedures of the various

components of the traffic monitoring program can provide an

avenue for facilitating training, reviewing performance, and

identifying opportunities that can lead to corrective action

when necessary.

Personnel

Traffic monitoring personnel represent a critical component

of a successful program. Personnel will require training to

effectively perform their duties. The training should include the

following:

Proper procedures for conducting traffic counts;

Procedures for placing, retrieving, and maintaining

automatic counters;

Proper procedures for monitoring performance

standards of equipment;

Proper procedures for data analysis, sample

estimations, and factoring; and

Proper procedures related to safety considerations.
22

Properly educating personnel will lead to a more motivated 

and dedicated work team generating consistent quality in data

and greater safety awareness of staff resources. Reference

materials are available to assist in this training and some have 

been listed in the back of this document. 

Equipment

Traffic monitoring equipment is another critical component

of a successful program. All equipment must be properly

functioning and personnel must have a good working

knowledge of the equipment to ensure valid data. Performance

standards should be established to address factors such

as equipment tolerances and failure rates and equipment

down time durations to assist in determining availability 

and scheduling of equipment. Testing schedules should be

established to ensure all equipment is operating properly. This

can be performed by conducting a manual count simultaneously

during an automatic count and comparing the results.

A general rule-of-thumb to follow is that the equipment is

working properly if a comparison manual count is:

Within ± 10 percent of a portable (road

tube) automatic count;

Within ± 2 percent of a permanent

(inductive loop sensor) automatic count;

Within ± 10 percent of a vehicle classifier

automatic count; and

Within ± 15 percent of a weigh-in-motion

GVW automatic count.

Quality assurance can be achieved through the establishment 

of procedures which document all activities related to a traffic

monitoring program.

Equipment maintenance records provide the basis for 

evaluating equipment performance, anticipating problems, 

developing replacement cycles, evaluating new equipment, and 

documenting budget issues. (AASHTO Guidelines, 1992)
23

Count Data

Count data that is collected from the traffic monitoring program

must be checked for validity to ensure quality control has

been achieved. Corrupted data should not be included in the

database. Corrupted data can be caused by an equipment

malfunction due to a power failure, a sensor malfunction, or a

communication error. These malfunctions will typically show

up in the data as a series of “0” recordings or as a series of

extremely high values for vehicle volume locations. In weigh-inmotion counts, invalid data recordings may be due to vehicles 

not passing over the sensor properly. This data should not be

included in any summarization reports, but should be retained 

for training and audit purposes.

Data collected during holidays, sporting events, parades, or 

traffic incidents are referred to as “atypical” (10). This type

of data should be analyzed with scrutiny and may need to be

excluded from any summarization reports, unless the specific

purpose was to monitor this type of event. Extended periods

of inclement weather are also considered “atypical” and are

usually excluded from analysis, especially for short term counts.

Data Analysis, Summarization, & Reporting

Data analysis and summarization of the data collected from

traffic counts is another critical part of a traffic monitoring

program. General principles have been established to ensure

that traffic data is analyzed and summarized in a consistent

manner from one agency to the next. Data analysis involves

the examination of the traffic data to determine any variability

in traffic that can be used to identify travel patterns or trends

over time. Understanding and identifying the variability in

traffic will assist in determining, applying, and evaluating

adjustment factors for traffic counts.

Variability in Traffic

The variability in traffic is inherently derived from a large

transportation system that enables a diverse multitude of

users to travel at various times and days. That is, traffic can

vary from day-to-day, week-to-week, and season-to-season. 

Additionally, traffic can vary by location, such as comparing

traffic data from different road types or comparing traffic data

from different regions within a state.

This variability in traffic must be taken into account when

trying to compare traffic counts from one location to another

because different types of counts and equipment may have
24

been used at different locations. For instance, one site may use

a permanent counter which counts traffic everyday of the year. 

This site could be used to examine the seasonal variability and 

trends that may exist at that location. This information could

then be used to develop seasonal adjustment factors that can

be applied to other locations within the area that use shortduration counts.

In another example, a count location may use a portable 

counter that collects classification data over several weeks. 

This site could be used to examine the variability in vehicle type 

that may exist at that location. This information could then be

used to develop axle correction factors that can be applied at

other count locations within the area to estimate traffic volumes

more accurately.

Factoring Counts

Adjustment factors are needed to modify traffic counts in order

to account for the variability in traffic. Adjustment factors can

be calculated for various uses including adjusting seasonal

variations in traffic, adjusting axle counts to vehicle volumes,

and providing annual growth estimates.

It should be noted that care must be taken when using 

adjustment factors to ensure the proper application of the 

factors in order to reach an accurate conversion. Most State 

highway agencies have established traffic monitoring programs 

and have the experience to assist in correctly applying 

adjustment factors.

Initially, “factor groups” are developed within a traffic

monitoring program to determine how continuous and shortduration counts can be compared to other similar locations. 

One method is done by grouping roadway types by their 

respective functional classification. This allows for the

adjustment factors from a “sample” roadway that behaves or

operates in a particular manner to be applied to similar roadway 

types in the same region. Another method is referred to as a

cluster analysis. This method determines which count stations

are most similar based on a statistical algorithm. It may be

that neither of these methods will work as a “factor group” for a

particular area. In that case, the agency will have to determine

an appropriate “factor group” plan.

Short-duration traffic counts are conducted in order to help

reduce costs of traffic monitoring programs by extending the

use of staff and equipment to multiple locations for shorter

periods of time. Consequently, adjustment factors are needed

to adjust short-duration traffic counts, which may include only a
25

few days of data, into an annual estimate of daily traffic. This is

typically performed by utilizing appropriate adjustment factors

derived from nearby continuous count locations, such as ATR

locations, which have a similar “factor group.”

The most common approach to converting a short-duration 

count to an annual average daily traffic (AADT) estimate utilizes

the following equation:

Source

Traffic Monitoring Guide, FHWA, May 2001.

AADThi = VOLhi * Mh * Dh * Ai * Gh

 where

AADThi = the annual average daily travel at location i of factor group h

VOlhi = the 24 hour axle volume at location i of factor group h

Mh = the applicable seasonal (monthly) factor for factor group h

Dh = the applicable day of-week factor for factor group h (if needed)

Ai = the applicable axle correction factor for location i (if needed)

Gh = the applicable growth factor for factor group h (if needed)

Conversely, the same equation can be used to compute a

particular adjustment factor (i.e., seasonal, day-of-week, axlecorrection or growth) from a continuous count location. To

calculate this, the observed AADT from an ATR is divided by the

various factors (if applicable) to obtain the desired adjustment

factor to be used for that particular “factor group.”

Factoring Methods within Parks

Park and recreational roadways typically have different

travel variability and travel patterns than rural or 

urban roadways. Therefore, it may not be appropriate
26

to arbitrarily apply the same methodology as used on 

highways, to collect and adjust short-duration counts on

park and recreational roadways.

Extending Count Period

Many park facilities only collect 48-hour short-duration

counts, typically due to budget constraints and/or 

personnel limitations. While this methodology may apply

well for urban commuter routes where travel patterns

are more predictable, it does not effectively capture the

variability of recreational traffic in and around parks.

It is suggested that to accurately capture day-of-week 

variations in recreational traffic, the traffic monitoring 

program should conduct short-duration counts for a period 

longer than 48 continuous hours (preferably one-week) 

made in different months.

While this practice may include a longer and more costly 

short term budget, research has shown that within a given 

park “the traffic patterns observed during each day-of-week

and month-of-year combination were not statistically different

from one year to the next” (16). This implies that shortduration counts could be adjusted using historical AADT data,

if that data is more statistically valid, and therefore, fewer

counts might be conducted from year to year.

Interagency Cooperation

In some instances there may not be a continuous counter 

available, for example within a park facility, that can be used

to acquire adjustment factors which could then be applied to

short-duration count locations within the park.

It may be appropriate to utilize nearby continuous counters 

from another agency (i.e. State, County, City, etc.) to obtain 

adjustment factors that could be applied to the short-duration 

counts within the park.

Through inter-agency cooperation, costs to collect the count 

information could be reduced by sharing the effort between

different agencies. It has been shown that roadways located

within close proximity (less than 20 miles) of parks have similar

variability characteristics (16). Once again, the “factor group”

must be considered when utilizing adjustment factors that are

obtained from outside “similar” locations. Recreational traffic in

and around parks will have different variability when compared

to the traffic on rural or urban roads not within the immediate

vicinity of the park.
27

6

5

4

3

2

1

0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Ratio of Annual Average Daily Traffic (AADT) to

Monthly Average Daily Traffic (MADT)

Sun Mon Tue Wed Thu Fri Sat

2002 2003 2004 2005 2006

1.00

.90

.80

.70

.60

.50

.40

.30

.20

.10

.00

Ratio of Annual Average Daily Traffic (AADT) to

Monthly Average Day Of The Week (MADT) Traffic

Monthly Adjustment Factors at Yosemite National Park

Day-of-Week Adjustment Factors for July at Yosemite National Park
28

Reporting Data

Reporting of traffic count data is performed after it has been

collected, analyzed, and summarized. Quality traffic related

decisions can be made and improved through the effective

reporting of the traffic data. Presentation of the data can take

many forms including standard reports, tables, and graphical

representations. The reports and tables might include

summaries of vehicle volume, vehicle classification, or weight

measurements as relevant to decision maker needs.

Graphical presentation of data will help to show the

representation of adjustment factors more clearly. Seasonal

factors being shown from month to month will show the

differences in travel patterns related to seasonal influences

while day-of-week factors will show the variations of travel on a

daily basis (see example figures).
29

Data Storage

Retention and storage of traffic data is another important

aspect of a successful traffic monitoring program. Data

retention guidelines are generally based on length 

requirements set forth by the agency that is performing the

traffic monitoring program and are based on the following (9):

The legal requirements of a governmental (county,

state, federal, etc.) agency;

The required data retention periods of other related data;

The utilization of the data;

The availability of computer resources;

The life expectancy, space requirements, and cost of

data storage resources; and

The available budget for the current and future years.

At a minimum, data to retain should include all original or “raw” 

traffic data collected as well as dates and times of efforts,

all adjustment factors, and all adjusted traffic data including

data that has been analyzed and summarized into reports. 

This information may be accessed in the future to determine

trend patterns over time. Additionally, all methodology and

guidelines related to the traffic monitoring program should be

retained for auditing and training purposes.

Over time a traffic monitoring program will collect a large

amount of data that needs to be stored (or warehoused) on a

medium which can be easily accessed at a later date. Data

storage can include such common current storage devices as 

a computer server drive, a portable hard drive, or digital video 

disk (DVD). These generally low cost storage devices allow

for dependable long-term storage of data while providing the

functionality needed to access the data for analysis. In some

instances, various companies offer a secure web site for the

storage of large amounts of data. The medium chosen to store

the data should be updated to new formats that conform to

the modernization of technology as needed. It is suggested

that off-site storage of duplicate data can provide additional

protection from fire or other actions deemed hazardous.
30
STRATEGIES FOR 

UNDER-FUNDED PROGRAMS
32

Some of the costs associated with a traffic monitoring program

remain relatively constant for any implemented plan including

the costs associated with data analysis, summarization, storage, 

and retention. However, some traffic monitoring costs that can

vary greatly include the cost of the automatic counter type in

combination with the detector type, and need to be chosen to 

best meet the needs of an agency. Automatic traffic counter

models differ in costs depending on the sophistication of the

equipment. Some general cost estimates that can be expected

for automatic traffic counters per unit as of 2004 include:

Portable accumulative count recorder (ACR) $900

Permanent automated traffic recorder (ATR) $1,615

Permanent automated vehicle classifier (AVC) $1,855

Portable weigh-in-motion (WIM) recorder $8,606

Permanent weigh-in-motion (WIM) recorder $65,000

A good quality traffic monitoring program will incorporate

strategies that utilize a mix of data collection techniques that

best meet the needs of the agency. Automated traffic recording

devices and corresponding detector types can be selected 

for various situations that will enable an agency on a limited

budget to obtain the needed traffic information. For example,

a portable accumulative count recorder (ACR) and pneumatic 

road tube sensors are an inexpensive yet extremely easy and 

useful set of traffic data collection tools. This combination of

traffic monitoring equipment can be placed, retrieved, and

moved to obtain short-duration traffic related information at

numerous locations.

Another strategy to explore is the use of simple manual traffic

counts that may be collected on a monthly basis, for instance

visitation counts to a park or recreational area. This data

can be manually collected easily in the form of a user-defined

vehicle classification count and/or vehicle occupancy count. 

This type of data collection effort can provide a range

of information to be used by an agency, for instance, in

determining peak hour vehicle trends or the total number of

persons at a particular location at any given time. Additionally,

monthly variation can be derived if the visitation information is

collected on a consistent basis. From this information, monthly

adjustment factors can be acquired that could be applied to

other short-duration counts within the area.

As stated previously in this document, another strategy to 

reduce costs of a traffic monitoring program is to coordinate

with external agencies to acquire useful information, such as
33

data from nearby traffic count locations managed by State

department of transportation agencies. Such coordination will

help reduce the effort and limit possible redundant collection

of travel information. This data can be a good source for

establishing adjustment factors which could be used to adjust

traffic data from short-duration daily counts to annual count

estimates. 
34

Detector Type 

Example Products 

Detection Accuracy 

COUNT WEIGHT CLASSIFICATION 

Inductive Loop Detectors (ILDs) EXCELLENT NA FAIR 

Not affected by weather performs well under high and

low volume traffic

Video Image Detectors (VIDS) FAIR NA POOR 

Peek Video Track 900

Autoscope 2004

Eliop Trafico EVA 2000

Occlusion and light conditions reduce accuracy 

weather related problems poor performance in high

density locations

Active Infrared Detectors EXCELLENT NA FAIR 

Schwartz Autosense I Weather related problems poor performance in high

density locations 

Microwave Detectors EXCELLENT NA NA 

Remote Traffic Microwave Sensor

(RTMS)

Peek PODD 

Whelen TDN-30

Not affected by weather

Passive Acoustic Detectors FAIR NA POOR 

Smartsonic TSS-1

SmarTek SAS-1 Poor performance in echo-filled environment

Passive Magnet Detectors EXCELLENT NA FAIR 

3M Canoga Vehicle Detection System 

702

Not affected by weather performs well under high and

low volume traffic

Piezoelectric Detectors EXCELLENT EXCELLENT EXCELLENT 

Accurate date to within ± 15% GVW 

Bending Plate for WIM EXCELLENT EXCELLENT EXCELLENT 

Accurate date to within ± 10% GVW 

Pneumatic Detector FAIR NA FAIR 

Road Tube

Weather related problems poor performance under

low speeds performs well under moderate

volume traffic

Manual Data Collection EXCELLENT NA EXCELLENT 

Personal Labor and Equipment Not affected by weather performs well under high and

low volume traffic for short periods of time

The above table compares various detector types available 

and their corresponding capabilities, limitations, and estimated 

costs as of the year 2004.
35

Installation 

Maintenance 

Needs 

Costs *

SETUP CALIBRATION INSTALLATION MAINTENANCE 

MODERATE EASY HIGH HIGH MEDIUM

Must block traffic for installation

high rate of installation errors

Weakens 

pavement $1447 per lane to install

DIFFICULT MODERATE MEDIUM HIGH MEDIUM

Requires a pole for mounting $1178 per lane to instal

EASY MODERATE LOW HIGH HIGH 

Requires a pole for mounting $1658 per lane to install

EASY MODERATE MEDIUM MEDIUM LOW

Requires a pole for mounting can

be mounted overhead or on side 

of road (sidefire)

$1086 per lane to install

EASY EASY LOW MEDIUM LOW

Requires a pole for mounting can

be mounted overhead or on side 

of road (sidefire)

$913 per lane to install

EASY EASY LOW LOW LOW

Can be installed under pavement 

by horizontal drilling or installed 

under overpass

$755 per lane to install

DIFFICULT DIFFICULT HIGH HIGH HIGH 

Must block traffic for installation

stringent site requirements

$ 1894 (AVC) per lane to install

$3360 (WIM) per lane to install

DIFFICULT DIFFICULT HIGH HIGH HIGH

Must block traffic for installation

stringent site requirements

Frequent

recalibration $3360 (WIM) per lane to install

EASY EASY MEDIUM LOW LOW 

Cannot be used in rutted 

pavement locations

Road tubing 

replacement

up to $100 per locations to setup 

and retrieve

NA NA NA MEDIUM LOW

Varies due to cost of personnel and type

of count performed

Notes: NA - Not Applicable

*cost estimates for comparison purposes only and include sensor and

installation costs (labor, travel, and misc. parts). Estimate does not

include cost of traffic control or power and communications installation as

dependant upon location.
36
LIST OF RESOURCES 

FOR ASSISTANCE 
38

1.	 Travel Monitoring. Policy information web page. Federal

Highway Administration, U.S. Department of Transportation. 

Washington D.C. September 2008. http://www.fhwa.dot.gov/

policy/ohpi/travel/index.cfm

2.	 Traffic Monitoring Guide. FHWA-PL-01-021. Office of Highway

Policy Information, Federal Highway Administration, U.S.

Department of Transportation. Washington D.C. May 2001. 

http://www.fhwa.dot.gov/ohim/tmguide/index.htm

3.	 Traffic Detector Handbook: Third Edition. FHWA-HRT-06-108. 

Office of Operations Research and Development, Federal

Highway Administration, U.S. Department of Transportation. 

Washington D.C. October 2006. http://www.tfhrc.gov/its/

pubs/06108/index.htm

4.	 Traffic Monitoring and Pavement Design Programs. Online 

training. Federal Highway Administration, U.S. Department

of Transportation. Washington D.C. April 2006. https://

admin.na3.acrobat.com/_a55098539/traffmonwbt/

5.	 Traffic Monitoring Guide - Training Mini-course. PowerPoint 

presentation. Office of Highway Policy Information, Federal

Highway Administration, U.S. Department of Transportation. 

Washington D.C. September 2008. http://www.fhwa.dot.gov/

policy/ohpi/hss/presentations/minicourse.ppt

6.	 National Park Service 2004 Traffic Data Report. Eastern 

Federal Lands Highway Federal Highway Administration, 

U.S. Department of Transportation. Washington D.C. June

2005 http://www.efl.fhwa.dot.gov/files/programs/nps-trafficdata/2004_NPS_Traffic_Data_Report.pdf

7.	 Traffic Monitoring in Recreational Areas Final Report. 

DTFH71-D-00009. Office of Highway Policy Information,

Federal Highway Administration, U.S. Department of

Transportation. Washington D.C. November 2009. 

8.	 Highway Performance Monitoring System Field Manual for

the Continuing Analytical and Statistical Database. Office of

Highway Policy Information, Federal Highway Administration,

U.S. Department of Transportation. Washington D.C. May

2005. http://www.fhwa.dot.gov/ohim/hpmsmanl/hpms.cfm 

9.	 AASHTO Guidelines for Traffic Data Programs. American 

Association of State highway and Transportation Officials. 

Washington D.C. 1992.

10.	 AASHTO Guidelines for Traffic Data Programs, 2nd edition.

American Association of State highway and Transportation

Officials. Washington D.C. 2001.
39

11.	 Traffic Data Request Guide for Highway Pavement and

Geometric Design. 5-1801-01-P1. Texas Department of

Transportation. May 2004. http://tti.tamu.edu/documents/5-

1801-01-P1.pdf

12.	 Manual of Transportation Engineering Studies. Robertson, 

Douglas H. Institute of Transportation Engineers. 

Washington D.C. 1994.

13.	 Traffic Engineering Handbook, 4th Edition. Pline, James L. 

Institute of Transportation Engineers. Washington D.C. 1992.

14.	 Transportation Planning Handbook, 3rd Edition. Meyer, 

Michael D. Institute of Transportation Engineers. 

Washington D.C. 2009.

15.	 Traffic Counting Procedures and Information Systems. 

Traffic Count Subcommittee. North Central Texas Council of

Governments, 1990.

16.	 Analysis of Seasonal and Day-Of-Week Traffic Patterns at

National Parks. Transportation Research Board. Washington

D.C. 2009.

17.	 Highway Capacity Manual. Transportation Research Board. 

National Research Council, Washington D.C. 2000.
notes
ACRONYMS

AADT Annual Average Daily Traffic

ACR Accumulative Count Recorder

ADT Average Daily Traffic

ATR Automatic Traffic Recorder

AVC Automatic Vehicle Classifier

DVD Digital Video Disc

FHWA Federal Highway Administration 

GVW Gross Vehicle Weight

NPS National Park Service

PHV Peak Hour Volume

RTMS Remote Traffic Microwave Sensor

VC Vehicle Classification

VMT Vehicle Miles Traveled 

WIN Weigh-In-Motion
Technical Report published by:

Technology Deployment Program 

Western Federal Lands Highway Division 

Federal Highway Administration 

610 East 5th Street 

Vancouver, WA 98661

For more information or

additional copies contact:

Amit Armstrong, Ph. D., P.E.

Phone: 360.619.7668

Fax: 360.619.7846

Amit.Armstrong@dot.gov