TRAFFIC MONITORING GUIDE

*SUPPLEMENT*

**April 2008**

**U.S. Department of Transportation**

**Federal Highway Administration**

**Office of Highway Policy Information**

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Section 4S

Vehicle Classification Monitoring

*Supplement*

**CONTENTS**

*Chapter* *Page*

INTRODUCTION 4S-1

TRAFFIC DATA COLLECTION AND MOTORCYCLES 4S-2

MOTORCYCLE CORRECTION FACTORS 4S-5

TRAFFIC MONITORING DATA FORMATS 4S-7

FHWA VEHICLE CLASSES 4S-9

RESOURCES ON TRAFFIC DATA COLLECTION 4S-11

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**Section 4 *Supplement***

**Introduction**

The 2001 edition of the *Traffic Monitoring Guide* (TMG) expanded
Section 4 on vehicle classification and promoted increased traffic
monitoring by vehicle class. However, the emphasis was on monitoring
truck movements and the special considerations that apply to monitoring
motorcycles was not covered. This Supplement to Section 4 addresses this
deficiency.

Motorcycles are the most dangerous motor vehicles for both operators and
passengers of any age. Moreover, data from the NHTSA's Fatality Analysis
Reporting System (FARS) indicate disturbing trends in motorcycle safety:

-   In 2006, motorcycle rider fatalities increased for the ninth
    consecutive year since reaching the lowest level in 1997 from 2,116
    in 1997 to 4,810 in 2006 -- an increase of 127 percent.

-   Trends accompanying the rising motorcyclist death toll include a
    dramatic increase in motorcycle ownership, particularly by riders
    over 40, along with changes in other factors such as motorcycle
    size.

-   The rate of increase in fatalities has outpaced the rate of increase
    in motorcycle registrations.

In order to assess motorcycle safety it is necessary to know the number
of crashes as well as the corresponding exposure to determine a fatality
rate. One of the key exposures are the motorcycle miles traveled:

-   Motorcycle exposure data are used to inform national decisions and
    establish motorcycle related policies and safety countermeasure
    programs.

-   Motorcycle exposure data are an important part of current safety
    performance measures, which measure the number of motorcycle
    fatalities per vehicle registrations and per million miles traveled.

-   Motorcycle travel data, especially by roadway functional system,
    helps the DOT to better understand the distribution of travel and
    devise effective design and operational measures for both reliable
    and safe travel of motorist. Motorcycle travel data is a critical
    element used in developing effective safety countermeasures.

The Highway Performance Monitoring System (HPMS) made it optional for
the reporting of motorcycle travel before 2007. Historically,
approximately 15% of the States did not report motorcycle travel, and
the FHWA estimated for these missing data in the table VM-1, *Annual
Vehicle Distance Traveled in Miles and Related Data by Highway Category
and Vehicle Type*. **This Supplement revises the TMG to provide guidance
to States on the collection and accurate reporting of motorcycle
classification data.**

Traffic Data Collection and Motorcycles

The *Traffic Monitoring Guide* recommends that a vehicle classification
counting program should include both extensive, geographically
distributed, short duration counts and a smaller set of permanent,
continuous counters. **This guidance is extended to include motorcycle
counts for both continuous and short duration counting.**

Permanent counters provide an understanding of how typical motorcycle
travel varies by day of the week and season of the year. Permanent,
continuously operating, vehicle classification counters (CVC) are the
backbone of the vehicle classification program and should be maintained
to a high degree of accuracy.

As with traditional traffic volume counting, continuous classifiers must
be supplemented by classification coverage counts. A fairly large number
of short duration vehicle classification counts should be performed to
monitor movements of motorcycles and other vehicle classes on individual
roads. They should include data for all lanes and directions for a given
location.

Traffic is usually monitored during weekdays while a large portion of
motorcycle travel may take place on weekends. The relationship based on
continuous classification sites must be developed to adjust for
motorcycle undercounting and estimate motorcycle AADT.

The travel patterns for motorcycles are usually different than those for
cars or trucks but the data collection plans currently used tend to be
structured around understanding the movements of cars and trucks.
Motorcycle volume patterns are primarily recreational patterns although
commuter travel may be significant in some cases. Motorcycle travel is
heavily dependent on the day-of-week (higher on weekends), season
(higher in summer), and special events (e.g., rallies).

Some short counts should be taken during rallies and in places where
motorcyclists are known to travel. For example, two-lane rural roads
without much truck traffic should be counted if there is reason to
expect recreational travel. Special events and seasonal travel should be
annualized to represent AADT and accounted for in VMT estimates. AVC
systems should be placed on recreational routes with motorcycle travel.

Because of the difference between motorcycle travel and that of other
vehicle classes, to better estimate the annual average travel by
motorcycles on the roads, States should develop a process that factors
short duration motorcycle counts, as well as the other vehicle classes.
Without adjustment, short duration classification counts yield biased
estimates.

A State DOT should be able to provide users with an estimate of the
amount of traffic by vehicle class by road segment. Motorcycle volume
and percentage estimates should be available for the date when data were
collected and as annual average estimates corrected for seasonal and
day-of-week variation.

This data collection effort yields the basic motorcycle traffic
statistics needed on any given road including the geographic variability
and the time-of-day distribution at a variety of locations.

Sufficient locations must be monitored to meet HPMS requirements.
Motorcycle travel is reported under the HPMS summary travel as a
proportion of total travel by roadway functional class. The State should
have motorcycle and other vehicle class travel data for all of the
roadway functional classes. If the stations are sufficiently distributed
according to road type and by traffic volume, a simple average of the
observed proportions from all stations can be reported on the summary
travel table (see *HPMS Field Manual*).

In addition to the State and Metropolitan planning and research funds
available for traffic monitoring, because of their importance for
safety, other funding sources are available under SAFETEA-LU for
collecting motorcycle travel data:

-   Section 402, State and Community Highway Safety Grants: funds may be
    used for any highway safety purpose under Title 23.

-   Section 406, Safety Belt Performance Grants: funds may be used for
    any highway safety purpose under Title 23, or for improvement of
    hazardous roadway locations or features.

-   Section 408, State Traffic Safety Information System Improvement
    Grants: funds may be used only to improve State Traffic Safety
    Information Systems.

Axle, visual, and presence sensors are most frequently used for
collecting vehicle class volume information and each provide a different
mechanism for classifying vehicles. Within each of these three broad
categories are an array of sensors with different capabilities, levels
of accuracy, performance capabilities within different operating
environments, and output characteristics. Each type of sensor works well
under some conditions and poorly in others. For example:

-   Light axle weights, low metal masses, and narrow footprint make
    motorcycles harder to detect;

-   Motorcycles in parallel or staggered formation may confuse
    detectors;

-   Adjusting detector sensitivity for trucks may lead to reduced
    detection of motorcycles;

-   Some combination trucks may be misclassified as a single-unit truck
    followed by a motorcycle (the rear tandem axle).

Road tubes are relatively inexpensive and provide short, sharp signals
but may have a problem with groups of motorcycles. Side looking radar
provides length-based classification and detects motorcycles. Inductive
loops can work well if properly installed and maintained but they have
problems with motorcycles in groups or staggering and are hard to tune
for motorcycles. Accuracy can be improved by using inductive loop
signature technology. Quadrupole loops also known as figure "8" style
loop detectors have enhanced sensitivity for detecting motorcycles,
bicycles, and smaller cars.

Sensors that cover a small area such as magnetometers have problems
detecting motorcycles or groups of motorcycles. For axle sensors which
are staggered a motorcycle will usually hit one sensor but not both; the
system will likely record this as a vehicle with a missing axle
detection and classify it as a passenger car by default.

All vehicle classifiers need to be calibrated and tested, and it is a
good idea to involve motorcycles traveling in groups to ensure that
motorcycles are properly counted. It is also advisable to use a test
standard such as ASTM E2532-06, "Standard Test Methods for Evaluating
Performance of Highway Traffic Monitoring Devices."

If length-based classification is used, it should accommodate motorcycle
identification as one of the groups. Axle sensors, loops, and road tubes
which detect the presence of vehicles should be placed in the travel way
of motorcycles to assure their detection. Sensors which detect vehicles
over the width of a lane are preferable to those that are partial lane.

There are several vendors who claim their automatic vehicle
classification (AVC) equipment will detect motorcycles. The proper
installation and calibration of the AVC device may be a critical
component in its ability to count motorcycles. All vehicle classes are
important; no vehicle class should be shortchanged. **It is the
responsibility of each agency to make the best decision as to the types
of automatic vehicle classifiers to purchase, install, calibrate, and
maintain.**

**Motorcycle Correction Factors**

Current practice applies seasonal adjustments to the total volume and
then estimates volumes for vehicle types using the observed
classification proportions. This will work fine if the traffic profile
of all vehicle types is the same as the total volume profile. Otherwise,
traffic volume for some vehicle types will be under-estimated or
over-estimated.

The day of week traffic pattern for motorcycles differs from that of
other vehicle types so short counts for motorcycles need to be factored.
The TMG allows flexibility in the creation of day-of-week factors (see
page 3-20 of the TMG). It suggests that factors may be computed on an
individual basis (seven daily factors) or as combined weekday (Monday,
Tuesday, Wednesday, and Thursday) and weekend (Friday, Saturday and
Sunday) factors.

In practice, few counts are taken on weekends so the only data available
for weekends are from permanent traffic counters and classifiers. This
is a problem for motorcycles which may have significant weekend travel
on routes or areas that are not near a permanent classifier. **The
solution is either to install additional permanent vehicle classifiers
or to take class counts on weekends.**

***Example***

The following example shows how to estimate correctly the annual average
daily motorcycle traffic (AADMT). First, take the data from a permanent
automatic vehicle classifier and determine the monthly average daily
traffic (MADT) for the total volume. The seasonal (monthly) factors are
the ratio of the MADTs with the AADT.

+--------------------+------------------------+------------------------+
| **Month**          | **Monthly**            | **Monthly**            |
|                    |                        |                        |
|                    | **ADT**                | **Factor**             |
+--------------------+------------------------+------------------------+
| Jan                | 47,376                 | 1.05                   |
+--------------------+------------------------+------------------------+
| Feb                | 45,285                 | 1.10                   |
+--------------------+------------------------+------------------------+
| Mar                | 50,574                 | 0.99                   |
+--------------------+------------------------+------------------------+
| Apr                | 51,040                 | 0.98                   |
+--------------------+------------------------+------------------------+
| May                | 51,662                 | 0.97                   |
+--------------------+------------------------+------------------------+
| Jun                | 52,320                 | 0.95                   |
+--------------------+------------------------+------------------------+
| Jul                | 51,320                 | 0.97                   |
+--------------------+------------------------+------------------------+
| Aug                | 52,416                 | 0.95                   |
+--------------------+------------------------+------------------------+
| Sep                | 50,824                 | 0.98                   |
+--------------------+------------------------+------------------------+
| Oct                | 51,564                 | 0.97                   |
+--------------------+------------------------+------------------------+
| Nov                | 49,188                 | 1.02                   |
+--------------------+------------------------+------------------------+
| Dec                | 45,806                 | 1.09                   |
+--------------------+------------------------+------------------------+
| AADT               | 49,948                 | 1.00                   |
+--------------------+------------------------+------------------------+

Next calculate the average daily traffic by vehicle type for each day of
the week for the year. Then compute day-of-week motorcycle correction
factors (MCF) as the ratio of the annual ADMT and the day-of-week ADMT.

The table shows an example of the annual ADMT by day of week:

  ----------------------------------------- -----------------------------
  **Day**                                   **ADMT**

  Monday                                    396

  Tuesday                                   403

  Wednesday                                 405

  Thursday                                  428

  Friday                                    655

  Saturday                                  725

  Sunday                                    483

  *ADMT*                                    499
  ----------------------------------------- -----------------------------

1.  For the weekday ADMT, add the motorcycle counts for Monday, Tuesday,
    Wednesday, and Thursday; then divide by four.

2.  For the weekend ADMT, add the motorcycle counts for Friday,
    Saturday, and Sunday; then divide by three.

3.  Compute the weekday MCF = ADMT / weekday ADMT.

4.  Compute the weekend MCF = ADMT / weekend ADMT.

In this example:

1.  Weekday ADMT = (396 + 403 + 405 + 428) / 4 = 408

2.  Weekend ADMT = (655 + 725 + 483) / 3 = 621

3.  Weekday MCF = 499 / 408 = 1.22

4.  Weekend MCF = 499 / 621 = 0.80

So a short class count would first be factored for seasonality and then
for the day of week. As an example, at a short term monitoring site on
the same route as the above site 10 miles to the south, two class counts
were taken on weekdays in August with the following results for
motorcycles:

  ------------------------- ----------------------- ---------------------
  **Date**                  **ADMT**                **ADT**

  Aug. 14                   518                     50,761

  Aug. 15                   494                     51,231

  *Average*                 506                     50,996
  ------------------------- ----------------------- ---------------------

The average of the two counts is adjusted by the seasonal factor for
August, which is 0.95:

506 0.95 = 481

However, this result is low unless it is adjusted by the weekday MCF:

481 1.22 = 586

So weekday motorcycle counts are increased to estimate the annual ADMT.
This takes into account the likelihood of higher weekend motorcycle
travel. The other vehicle classes would need to be adjusted for the day
of week, too, so that the total volume is correct.

**Traffic Monitoring Data Formats**

Travel monitoring data should be submitted to the FHWA via the Travel
Monitoring Analysis System (TMAS). TMAS includes the monthly volume data
for the Traffic Volume Trends and will include vehicle classification
and truck weight data that in the past were processed with the Vehicle
Travel Information System (VTRIS).

TMAS is accessed via the FHWA's User Profile and Access Control System
(UPACS). The UPACS link is:
[https://fhwaapps.fhwa.dot.gov](https://fhwaapps.fhwa.dot.gov/). For
further information on accessing TMAS, contact your FHWA Division Office
or the FHWA Travel Monitoring Team.

The record formats are specified in Section 6 of the *Traffic Monitoring
Guide*. It is important that the *Station Description Record* be filled
out completely because it is required by TMAS. Fields that are not
applicable should be blank. In particular, if field 13 is zero, then
fields 12, 14, 15, and 16 may be blank; if field 18 is zero, then fields
17, 19, and 20 may be blank.

Field 16 of the *Station Description Record*, the Vehicle Typology
(formerly the Classification System for Vehicle Classification), is now
a critical field because it will be used to determine the number of
vehicle types in the corresponding *Vehicle Classification Records*. A
typology is simply the total number of vehicle types with a description
of how each vehicle type relates to the FHWA 13-class typology.

For example, a typology based on vehicle length may have 3, 4, or 5
vehicle types, whereas a typology based on axle spacings should have at
least the 13 FHWA vehicle classes. *The implied typology for 5 vehicle
types now classifies motorcycles as a separate vehicle type.*

16\. **Vehicle Typology** (Columns 24‑25) - *Critical*

This field indicates the total number of vehicle types used at the
station and an implied description of what the vehicle types are. The
default value is 13 which indicates the standard FHWA 13-class typology.
The value for Vehicle Typology will determine the number of count fields
needed on the *Vehicle Classification Records* for that station. If a
typology is used that does not match one of these, attach a description
of the typology and how it relates to the FHWA 13-class typology.

In the following table the numbers in parentheses refer to the FHWA
13-class typology:

+------+---------------------------------------------------------------+
| **Co | **Description**                                               |
| de** |                                                               |
+------+---------------------------------------------------------------+
| 01   | One vehicle type: total volume                                |
+------+---------------------------------------------------------------+
| 02   | Two vehicle types as follows:                                 |
|      |                                                               |
|      | Type 1 = passenger vehicles (classes 1-3)                     |
|      |                                                               |
|      | Type 2 = trucks (classes 4-13)                                |
+------+---------------------------------------------------------------+
| 03   | Three vehicle types as follows:                               |
|      |                                                               |
|      | Type 1 = passenger vehicles (classes 1-3)                     |
|      |                                                               |
|      | Type 2 = buses and single-unit trucks (classes 4-7)           |
|      |                                                               |
|      | Type 3 = combination trucks (classes 8-13)                    |
+------+---------------------------------------------------------------+
| 04   | Four vehicle types as follows:                                |
|      |                                                               |
|      | Type 1 = passenger vehicles (classes 1-3)                     |
|      |                                                               |
|      | Type 2 = buses and single-unit trucks (classes 4‑7)           |
|      |                                                               |
|      | Type 3 = single-trailer trucks (classes 8‑10)                 |
|      |                                                               |
|      | Type 4 = multi-trailer trucks (classes 11-13)                 |
+------+---------------------------------------------------------------+
| 05   | Five vehicle types as follows (*revised*):                    |
|      |                                                               |
|      | Type 1 = motorcycles (class 1)                                |
|      |                                                               |
|      | Type 2 = two-axle, four-tire vehicles (classes 2-3)           |
|      |                                                               |
|      | Type 3 = buses and single-unit trucks (classes 4-7)           |
|      |                                                               |
|      | Type 4 = single-trailer combination trucks (classes 8‑10)     |
|      |                                                               |
|      | Type 5 = multiple-trailer combination trucks (classes 11‑13)  |
+------+---------------------------------------------------------------+
| 06   | Six classes as follows (*cf. HPMS Summary Travel form*):      |
|      |                                                               |
|      | Type 1 = motorcycles (class 1)                                |
|      |                                                               |
|      | Type 2 = two-axle, four-tire vehicles (classes 2-3)           |
|      |                                                               |
|      | Type 3 = buses (class 4)                                      |
|      |                                                               |
|      | Type 4 = single-unit trucks (classes 5-7)                     |
|      |                                                               |
|      | Type 5 = single-trailer combination trucks (classes 8‑10)     |
|      |                                                               |
|      | Type 6 = multiple-trailer combination trucks (classes 11‑13)  |
+------+---------------------------------------------------------------+
| 07   | Number of vehicle classes in the typology (attach a           |
| to   | description of how it relates to the 13 classes)              |
| 11   |                                                               |
+------+---------------------------------------------------------------+
| 12   | FHWA's 13-class typology except class 3 is missing (i.e.,     |
|      | classes 2 and 3 are combined)                                 |
+------+---------------------------------------------------------------+
| 13   | FHWA\'s 13-class typology                                     |
+------+---------------------------------------------------------------+
| 14   | FHWA\'s 13-class typology plus a class 14 (attach a           |
|      | description)                                                  |
+------+---------------------------------------------------------------+
| 15   | FHWA\'s 13-class typology plus classes 14 and 15 (attach a    |
|      | description)                                                  |
+------+---------------------------------------------------------------+

FHWA Vehicle CLASSEs

The FHWA vehicle typology separates vehicles into categories depending
on whether they carries passengers or commodities. Non-passenger
vehicles are further subdivided by the number of axles and the number of
units, including both power and trailer units. Note that the addition of
a light trailer to a vehicle does not change the classification of the
vehicle.

Axle-based automatic vehicle classifiers need an algorithm or "scheme"
to interpret axle spacing information and correctly classify vehicles
into these classes. The FHWA does not endorse any algorithm or scheme
for interpreting axle spacings. Axle spacing characteristics for
different vehicle classes are known to change from State to State. As a
result, no single algorithm is best for all cases. It is the
responsibility of each agency to test and calibrate the classification
algorithm they use.

*FHWA Vehicle Classes with Definitions*

1\. ***Motorcycles*** \-- All two or three-wheeled motorized vehicles.
Typical vehicles in this category have saddle type seats and are steered
by handlebars rather than steering wheels. This category includes
motorcycles, motor scooters, mopeds, motor-powered bicycles, and
three-wheel motorcycles. *Note that this vehicle class is now required*.

2\. ***Passenger Cars*** \-- All sedans, coupes, and station wagons
manufactured primarily for the purpose of carrying passengers and
including those passenger cars pulling recreational or other light
trailers.

3\. ***Other Two-Axle, Four-Tire Single Unit Vehicles*** \-- All
two-axle, four-tire, vehicles, other than passenger cars. Included in
this classification are pickups, panels, vans, and other vehicles such
as campers, motor homes, ambulances, hearses, carryalls, and minibuses.
Other two-axle, four-tire single-unit vehicles pulling recreational or
other light trailers are included in this classification. *Because
automatic vehicle classifiers have difficulty distinguishing class 3
from class 2, these two classes may be combined into class 2.*

4\. ***Buses*** \-- All vehicles manufactured as traditional
passenger-carrying buses with two axles and six tires or three or more
axles. This category includes only traditional buses (including school
buses) functioning as passenger-carrying vehicles. Modified buses should
be considered to be a truck and should be appropriately classified.

**NOTE:** In reporting information on trucks the following criteria
should be used:

a\. Truck tractor units traveling without a trailer will be considered
single-unit trucks.

b\. A truck tractor unit pulling other such units in a \"saddle mount\"
configuration will be considered one single-unit truck and will be
defined only by the axles on the pulling unit.

c\. Vehicles are defined by the number of axles in contact with the
road. Therefore, \"floating\" axles are counted only when in the down
position.

d\. The term \"trailer\" includes both semi- and full trailers.

5\. ***Two-Axle, Six-Tire, Single-Unit Trucks*** \-- All vehicles on a
single frame including trucks, camping and recreational vehicles, motor
homes, etc., with two axles and dual rear wheels.

6\. ***Three-Axle Single-Unit Trucks*** \-- All vehicles on a single
frame including trucks, camping and recreational vehicles, motor homes,
etc., with three axles.

7\. ***Four or More Axle Single-Unit Trucks*** \-- All trucks on a
single frame with four or more axles.

8\. ***Four or Fewer Axle Single-Trailer Trucks*** \-- All vehicles with
four or fewer axles consisting of two units, one of which is a tractor
or straight truck power unit.

9\. ***Five-Axle Single-Trailer Trucks*** \-- All five-axle vehicles
consisting of two units, one of which is a tractor or straight truck
power unit.

10\. ***Six or More Axle Single-Trailer Trucks*** \-- All vehicles with
six or more axles consisting of two units, one of which is a tractor or
straight truck power unit.

11\. ***Five or fewer Axle Multi-Trailer Trucks*** \-- All vehicles with
five or fewer axles consisting of three or more units, one of which is a
tractor or straight truck power unit.

12\. ***Six-Axle Multi-Trailer Trucks*** \-- All six-axle vehicles
consisting of three or more units, one of which is a tractor or straight
truck power unit.

13\. ***Seven or More Axle Multi-Trailer Trucks*** \-- All vehicles with
seven or more axles consisting of three or more units, one of which is a
tractor or straight truck power unit.

**Resources on Traffic Data Collection**

FHWA Travel Monitoring webpage

<http://www.fhwa.dot.gov/policy/ohpi/travel/index.htm>

*Traffic Monitoring Guide* (TMG)

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

*Traffic Detector Handbook: Third Edition*

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

Detector Technology Evaluation (2003)

<http://www.ndsu.nodak.edu/ndsu/ugpti/MPC_Pubs/pdf/MPC03-154.pdf>

Vehicle Detector Evaluation (2002)

<http://tti.tamu.edu/documents/0-2119-S.pdf>

<http://tti.tamu.edu/documents/2119-1.pdf>

Portable Non-Intrusive Traffic Detection System (PNITDS)

<http://www.dot.state.mn.us/guidestar/projects/pnitds.html>

Non-Intrusive Traffic Detection -- Phase II Final Report (2002)

<http://www.dot.state.mn.us/guidestar/projects/nitd.html>

[Traffic Monitoring Standards from ASTM International]{.underline}:

-   E1318-02 Standard Specification for Highway Weigh-in-Motion (WIM)
    Systems with User Requirements and Test Methods

-   E1957-04 Standard Practice for Using Pneumatic Tubing for Roadway
    Traffic Counters and Classifiers

-   E2259-03a Standard Guide for Archiving and Retrieving ITS-Generated
    Data

-   E2300-06 Standard Specification for Highway Traffic Monitoring
    Devices

-   E2415-05 Standard Practice for Installing Piezoelectric Highway
    Traffic Sensors

-   E2467-05 Standard Practice for Developing Axle Count Adjustment
    Factors

-   E2468-05 Standard Practice for Metadata to Support Archived Data
    Management Systems

-   E2532-06 Standard Test Methods for Evaluating Performance of Highway
    Traffic Monitoring Devices

-   E2561-07a Standard Practice for the Installation of Inductive Loop
    Detectors