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EVALUATION OF ARIZONA'S FATALITY RATE

ANALYSIS OF PROCEDURAL ISSUES

Prepared for
Arizona Department of Transportation
Arizona Transportation Research Center

Prepared by

JHK & Associates
and
University of Arizona
Department of Civil Engineering

February 20, 1987

associates

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TABLE OF CONTENTS

Page
1.

INTRODUCTION

1

2.

VEHICLE CLASSIFICATION STUDY PROCEDURES

3

3.

VEHICLE CLASS DESIGNATlONS

6

4.

VEHICLE DISTRIBUTION FACTORS B Y ROAD CLASS

5.

GASOLINE VERSUS DIESEL FUEL VEHICLES
IN THE ARIZONA TRAFFIC POPULATION

6.

ADOPTION OF MPC FACTORS

7.

REFERENCES

1. INTRODUCTION
T h e purpose o f t h i s technical memorandum is t o describe t h e results of
a c t i v i t i e s t o resolve t h e five procedural issues contained in Chapter 5 of the
Interim R e p o r t d a t e d O c t o b e r 30, 1986.

T h e resolution of t h e issues is a

prerequisite t o t h e finalization of t h e preferred V M T algorithm and i t s validation. A
brief summary of t h e issues i s provided below and a description of the analysis
a c t i v i t i e s and major conclusions a r e presented in t h e following c h a p t e r s of the
memorandum.
VEHICLE CLASSIFICATION STUDY PROCEDURES
This issue required t h e review of c u r r e n t ADOT d a t a collection procedures for
obtaining vehicle classification data. In particular, the procedure f o r sampling
vehicle classification d a t a on various road classes and t h e length of t h e data
collection period w a s reviewed. T h e review of c u r r e n t ADOT procedures considered
t h e research r e p o r t e d in t h e "Vehicle Classification Procedure Study" and the
vehicle classification d a t a currently being collected by ADOT.

VEHICLE CLASS DESIGNATIONS
This issue required t h e review and definition of vehicle t y p e designations for
use in t h e manual collection o f vehicle classification data.

The c r i t e r i a used t o

designate vehicle types was t o minimize t h e variance in mpg within e a c h roadway
class.
VEHICLE MIX FACTORS BY ROAD CLASS
This issue required t h e development of vehicle mix c h a r a c t e r i s t i c s for e a c h
roadway class t o b e used i n t h e VMT procedure. A review was conducted of existing
classification d a t a and t h e need f o r collection of supplemental data. T h e informat i o n obtained f r o m a n analysis of t h e s e d a t a is used t o verify o r adjust t h e vehicle
mix c h a r a c t e r i s t i c s within a given roadway class.

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GASOLINE VERSUS DIESEL FUEL VEHICLES
IN THE ARIZONA TRAFFIC POPULATION

This issue involved t h e differentiation of diesel vehicles from gasoline
vehicles.
When c o l l e c t i n g vehicle classification d a t a , differentiation between
gasoline and diesel powered vehicles i s difficult and sometimes impossible. The
p e r c e n t a g e s of diesel a n d gasoline powered vehicles within t h e t r a f f i c population
w e r e reviewed using Arizona vehicle registration d a t a .

ADOPTION OF hIPG FACTORS
This issue required t h e adoption of a n information source for mpg d a t a
selection of mpg e s t i m a t e s by vehicle class.

A review of t h e various mpg sources

was conducted t o d e t e r m i n e t h e source most appropriate for use in t h e VMT
algorithm.

2. VEHICLE CLASSIFICATION STUDY PROCEDURES
REVIEW OF ADOT VEHICLE CLASSIFICATION STUDIES
The Arizona D e p a r t m e n t of Transportation (ADOT) has a n ongoing program for
collecting d a t a on s t a t e w i d e vehicle classifications. Vehicle classification d a t a a r e
periodically collected a t 125 locations distributed throughout t h e s t a t e .

Vehicles

a r e classified by ADOT i n t o t h e following categories:
o Automobiles, station wagons, vans with rear windows and motorcycles.
o

C a m p e r recreational vehicles and motor homes.

o

School and Transit buses.

o Pickup trucks, pickups with shells or campers, panel trucks and vans
without r e a r windows.
o Single unit trucks with t w o a x l e dual t i r e s or t h r e e axles.
o

Tractor-Semi Trailer with three, four, or five axles.

o

Truck and Trailer with four, five, o r six axles.

o

Truck t r a i n s with five or six axles.

T h e number of d a t a collection s i t e s by roadway functional class in rural and
urban a r e a s i s shown in Table 1 along with t h e number of miles of e a c h functional
c l a s s within t h e s t a t e . F o r t h e years 1979 through 1984, 110 of t h e 125 s i t e s were
sampled a t l e a s t o n c e e a c h year. These 110 s i t e s were used in a n analysis of vehicle
c l a s s distributions by road class. T h e study sample included 103 s i t e s (93.6 percent)
on rural roads and seven s i t e s o n urban roadways.

F o r t h e rural roadways, 101

(98 percent) of t h e s i t e s a r e l o c a t e d on t h e four most highly sampled functional

classifications (principle arterial-interstate, principle arterial-other, minor arterial,
and major collector) and a r e e s t i m a t e d t o a c c o u n t for 81 p e r c e n t of t h e rural VMT.
T h e distribution of s i t e s and t h e number of samples taken on e a c h of these four rural
classifications was sufficient f o r s t a t i s t i c a l analysis.

T h e number of s i t e s and

s a m p l e s on t h e remaining t h r e e rural roads and on a l l of t h e urban roads was
considered inadequate t o r e p r e s e n t t h e s e functional classes f o r statistical analysis
(in t h e next issue).
Each s i t e was sampled b e t w e e n 10 and 14 t i m e s during t h e study period. T h e
s a m p l e periods w e r e t h r e e consecutive hours beginning between 7:00 AM and
2 0 0 PM.

A cursory review of t h e sample indicated t h a t a l l t h e samples were

obtained on weekdays.

This could bias an analysis of vehicle classification if

Saturdays a n d Sundays exhibited a significantly different vehicle mix. The existence
of such a d i f f e r e n c e c a n n o t b e determined with available information.
Table 1

NUMBER O F ADOT VEHICLE CLASSIFICATION SITES,
AND MILES OF ROADWAY BY ROADWAY FUNCTIONAL CLASSlFICATlON
Rural Hirhways
Functional Class

#I S i t e s

Miles*

Urban Highways
#/ S i t e s

Miles*

Principle Arterial--Interstate

28

1,021

3

129

Principle Arterial--Other

27

1,075

3

37 1

Minor A r t e r i a l

39

2,253

1

963

Major Collector

20

4,071

NA

NA

Minor Collector

2

3,825

NA

NA

NA
2

Collector

NA

924

Local

0

55,065

0

6,437

Total

116

67,313

9

8,824

Source: Highway S t a t i s t i c s 1984, USDOT, FHWA, Washington, D.C.,
NA = Not Applicable
+

1985.

A previous study f o r ADOT (1) indicated t h a t t h e hourly variation of vehicle

class i s minor and concluded t h a t t h e p e r c e n t of vehicles by class could be
considered c o n s t a n t throughout t h e day on rural highways. Therefore, t h e sampling
period and t h e r a t e of sampling f o r this study a r e considered m o r e t h a n adequate t o
base conclusions regarding vehicle class characteristics. T h e previous study did not
e v a l u a t e t h e p o t e n t i a l s h i f t in vehicle mix by day of week.
CONCLUSION
The c u r r e n t ADOT program t o sample s t a t e w i d e vehicle classification d a t a is
adequate as a s o u r c e of vehicle classification information f o r t h e following rural
roadway classifications.

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o Principle arterial--interstate

o Principle arterial--other
o Minor arterial
o

Major collector

Since these classifications are estimated to contain over 80 percent of the rural

VMT, current ADOT data provide an adequate database for analyzing and aggregating vehicle classes by rural roadway class.
ADOT vehicle classification data are insufficient for performing similar
analyses on urban road classes and limited supplemental data should be collected and
analyzed a s a part of this study.
The current ADQT vehicle classification program should be expanded to
include a representative sample of vehicle classification data on urban road classes.

3. VEHICLE CLASS DESlGNATlONS
METHODOLOGY
S t a t i s t i c a l analyses w e r e performed on the ADOT vehicle classification
d a t a b a s e described in t h e previous chapter.

Analyses were performed only on the

vehicle classification distributions f o r t h e foIlowing rural classes of roadway.
o

Principle arterials-interstate

o

Principle arterials--other

o

Minor a r t e r i a l s

o

Major collectors

ADOT d a t a w e r e not available in sufficient numbers t o allow t h e analysis for other
rural classes o r urban highways.
The vehicle classifications t h a t were analyzed included the eight classes
currently used in ADOT vehicle classification studies ( r e f e r t o the list of vehicle
t y p e s in C h a p t e r 2).
The o b j e c t i v e of t h e analysis was t o d e t e r m i n e if s e l e c t e d classes of vehicles
c a n b e combined t o r e d u c e t h e number of vehicle classes in t h e VMT algorithm.
T h e c r i t e r i a used t o establish the vehicle types t o be used in t h e VhlT
algorithm were:
o Physical c h a r a c t e r i s t i c s m u s t allow f o r t h e visual discrimination of vehicle
types.
o Vehicle t y p e designations should conform t o t h e existing classification
s c h e m e t o allow t h e use of existing d a t a and existing d a t a collection
procedures, if feasible.
o
o
o

Vehicle classes should represent significant portions of t h e vehicle population.
T h e r e should be significantly different fuel consumption characteristics
b e t w e e n vehicle classes.
Vehicle classes should a t t e m p t t o minimize t h e variance of fuel consumption c h a a c t e r i s t i c s within a particular road class.

CONCLUSION
T h e analysis resulted in t h e aggregation of t h e following four classes of
vehicles.

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Automobiles including: passenger cars, s t a t i o n wagons, vans with rear
windows and motorcycles.

o Light t r u c k s including: pickup trucks, pickups with shells o r campers, panel
trucks, and vans without r e a r windows.
o Medium trucks including: c a m p e r recreational vehicles, mobile homes,
school a n d t r a n s i t buses, and single unit t r u c k s with t w o axle dual t i r e s or
t h r e e axles.
o

Heavy t r u c k s including: tractor-semi trailer with three, four or five axles,
truck a n d trailer with four, five, or six axles, and t r a i n s with f i v e or six
axles.

T h e following c o m m e n t s a r e provided a s justification f o r aggregation of t h e
a b o v e vehicle classes.
o T h e automobile classification exhibits t h e l a r g e s t within group variation in
vehicle mpg.
This is due t o t h e large variation in vehicle mpg for
passenger c a r s of d i f f e r e n t types, and due t o t h e combining of vans with
r e a r windows and motorcycles into t h e "single vehicle" classification. Vans
with r e a r windows exhibit vehicle and rnpg c h a r a c t e r i s t i c s t h a t a r e similar
t o those of light t r u c k s and therefore should logically be grouped i n t o the
light t r u c k classification. However, t h e existing ADOT vehicle classification s c h e m e is based on t h e travel function (or purpose of vehicle
utilization) and physical characteristics of t h e vehicle. Hence, vans with
r e a r windows, which a r e typically used for carrying passengers, a r e grouped
with o t h e r passenger vehicles.
T h e proportion of vans within the
automobile group is unknown, and could n o t be disaggregated from the
ADOT data. The proportion of motorcycles within t h e ADOT d a t a is also
unknown. However, a previous ADOT study (1) collected vehicle classification d a t a with motorcycles as a s e p a r a t e group. This study indicated t h a t
motorcycles a c c o u n t e d f o r a maximum of 1.5 p e r c e n t and a minimum of
0.6 p e r c e n t of t h e vehicles on rural roads, with a mean value of 1.1
percent. Thus, t h e influence of motorcycle mpg c h a r a c t e r i s t i c s is not
significant within t h e automobile classification on rural roads. Furthermore, t h e bias produced by motorcycles may b e o f f s e t somewhat by t h e
inclusion of t h e vans with r e a r windows in t h i s group ( t h e proportion of
vans in this c l a s s i s a l s o very small).
o Pickup trucks with c a m p e r s a r e grouped with c a m p e r recreational vehicles
in t h e ADOT classification schedule.
A D 0 7 procedures require d a t a
c o l l e c t o r s t o c o u n t pickups with c a m p e r s i n t h e classification with other
pickups and v a n s without r e a r windows. Hence, t h e designation of this
vehicle t y p e in t h e light t r u c k category. T h e light t r u c k s satisfy a11 of t h e
c r i t e r i a f o r designation as a s e p a r a t e vehicle classification.
o C a m p e r recreational vehicles and motor h o m e s a r e , in general, single unit
t r u c k s with modified bodies. These vehicles generally have t h e weight and
o p e r a t i n g c h a r a c t e r i s t i c s of single unit t r u c k s as well. Therefore, i t was
logical to a g g r e g a t e t h i s vehicle type i n t o t h e medium truck classification.
This s a m e reasoning w a s applied t o t h e grouping of t r a n s i t a n d school buses
i n t o t h e medium t r u c k classification.

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A review o f the available fuel consumption characteristics (see discussion
of mpg values) indicated that above a weight of approximately 19,000
pounds, large trucks exhibit very similar mph characteristics regardless o f
t h e other physical differences in the vehicles. Therefore, tractor-semi
trailers, truck and trailers, and truck trains may be aggregated into a
"heavy truck" classification.

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4, VEHICLE DISTRlBUTION FACTORS BY ROAD CLASS

The analysis of vehicle distributions concentrated on t h e four rural functional
classifications f o r which t h e r e w e r e sufficient data. These are:
o

Principle Arterial--Interstate

o

Principle Arterial--Other

o

Minor A r t e r i a l

o

Major Collector

Statistical analyses were conducted t o t e s t f o r differences in vehicle mix between
roadway functional classifications.

CONCLUSlONS
The analysis produced t h e following conclusions:
o

Vehicle distributions f o r rural i n t e r s t a t e s and rural non-interstates
(aggregated) were significantly different.

o

Vehicle distributions f o r t h e rural non-interstates were significantly
different, due primarily t o t h e large vehicle classification sample size
available f o r analysis. Practically, however, t h e distributions do not differ
substantially when t h e p e r c e n t a g e of vehicle types a r e compared across
road class. Table 2 shows t h e percentages of the vehicle types identified in
t h e preceeding c h a p t e r f o r t h e t h r e e classes of rural non-interstates.
Table 2

VEHICLE CLASS DISTRIBUTIONS
FOR RURAL NON-INTERSTATES
Rural Road C l a s s

Auto
-

Principle-Other
Major Arterial
Major Collector
Average

56.8
56.2
59.3
57.2

Vehicle Class
Light Truck
Medium Truck
8.0
30.5
8.3
33.2
5.9
31.9
7.6
31.8

Heavy Truck
4.7
2.3
2.9
3.5

A sensitivity analysis f o r t h e r u r a l non-interstate group was performed t o
e s t i m a t e weighted rnpg using a n a v e r a g e (combined--over t h e rural noni n t e r s t a t e s ) percentage versus t h e individual p e r c e n t a g e s f o r e a c h road
class. T h e weighted mpg's produced in t h i s analysis differed by 0.3 mpg o r
by 1.6 percent. This relatively small difference justifies t h e aggregation of
rural non-interstates despite t h e observed s t a t i s t i c a l difference.

o

T h e vehicle distribution on rural i n t e r s t a t e s was very stable over t h e six
y e a r study period with very small fluctuations a b o u t t h e mean in the
p e r c e n t vehicles by vehicle type. Vehicle distributions on rural noni n t e r s t a t e s showed a similar t i m e stability.
Adjustments in vehicle
distribution t r e n d s over t i m e is n o t warranted.

o T h e vehicle distribution by month of y e a r by roadway functional classification i s significantly different. All vehicle classes w e r e shown t o f l u c t u a t e
significantly with t h e exception of medium-duty trucks. Aggregation of
t h e d a t a i n t o t h e "rural interstate" and "rural non-interstate" classes
verifies this finding. T h e distribution of vehicle mix displayed in t h e s e
f i g u r e s suggest4 seasonal variations in t h e s e characteristics.
o Vehicle mix differences on rural roadways by region within t h e S t a t e was
shown t o be statistically significant. However, d u e t o t h e large database
used in t h e analysis, practical significance (particularly, where t h e use o f
f u e l efficiency d a t a is concerned) was n o t achieved.
The evaluation of t h e regional variation in vehicle mix ws performed t o
d e t e r m i n e if t h e application of a s t a t e w i d e 'Impg" value f o r a defined
roadway class was appropriate or if significant regional differences in
vehicle class existed t o result in s p e c i f i c "mpg" values by region of state.
Regional boundaries used were identical t o those used in t h e previous
ADOT study "Vehicle Classification P r o c e d u r e Study" (FHWAfAZ84/195,1I).
T h e vehicle mix c h a r a c t e r i s t i c s by region a r e displayed in
T a b l e s 3 and 4 f o r rural i n t e r s t a t e s and rural non-interstates, respectively.
o Statistically significant differences in vehicle mix w e r e observed by region
and season of y e a r f o r t h e aggregation of "rural interstates" and ''rural noni n t e r s t a t e " classifications.
These differences, however, were not
significant f o r f u e l efficiency calculations.
T h e characteristics a r e
displayed in Tables 5 and 6. Seasonal designations w e r e a s follows:
Winter:
December, January, February
Spring:
March, April, May
Summer: June, Suly, August
Fall:
September, October, November
Based on t h e s e findings, vehicle mix sampling should t a k e into account t h e
seasonal and regional variation within t h e s t a t e . However, t h e e f f e c t of
t h e s e d i f f e r e n c e s on fuel efficiency (mpg) i s not considered significant.
Similar type analyses will b e conducted on t h e urban roadway classifications
following completion of t h e d a t a collection e f f o r t on urban roadways.

Table 3
VEHICLE MIX (%) BY REGION FOR INTERSTATE HIGHWAYS

Region

Light
Truck

Medium
Truck

Heavy
Truck

Weighted
MPG

-

Auto

-

1

56.5

14.9

9.4

19.2

16.7

2

56.4

18.8

9.5

15.4

17.1

3

58.8
-

17.3

8.1

15.7

17.3

57.7

17.1

8.8

16.4

17.1

TOTAL

Table 4 t,,;,,,.

VEHICLE MIX

Region

I

(%)

BY REGION FOR4INTERSTATE HIGHWAYS

Functional
Class
Principal ArterialOther
Minor Arterial
Major Collector

Light
Truck

Medium
Truck

Heavy
Truck

Weighted
MPG

54.9

3 1.6

8.5

4.9

--

53.7
62.9

35.1
29.1

8.5
5.8

2.6
2.2

--

Auto

--

18.6

Principal ArterialOther
Minor Arterial
Major Collector

58.6

24.0

8.7

8.7

59.1
56.8

30.3

8.4

34.6

5.8

2.2
2.7

--

---

18.8

Principal ArterialOther
hlinor Arterial
Major Collector
TOTAL

58.0

31.0

7.3

3.6

--

51.9
58.8
57.4

38.8
31.5
31.8

7.1
6.0

2.2

---

7.6

3.5

18.8

-

3.6
- - -

Table 5
VEHICLE MIX BY REGION AND SEASON FOR INTERSTATE ROADWAYS

Region

Season

I

Winter
Spring
Summer
Fall
TOTAL
Winter
Spring
Summer
Fal I
TOTAL
Winter
Spring
Summer
Fall
TOTAL

Auto

Light
Truck

-

Medium
Truck

-

Heavy
Truck

-

Total
-

Table 6

VEHICLE MIX BY REGION AND SEASON FOR NON-INTERSTATE ROADWAYS
Region

Season

1

Winter
Spring
Summer
Fall
TOTAL
Winter
Spring
Summer
Fall
TOTAL
Winter
Spring
Summer
Fall
TOTAL

Auto

Light
Truck

Medium
Truck

Heavy
Truck

31 .O
33.1
29.0
37.8
32.4
30.6
30.5
29.7
31.1
30.5
29.3
33.3
32.1
36.3
32.3

6.8
8.4
8.0
8.2
8.0
8.4
7.9
6.8
7.9
7.8
6.7
7.4
6.9
7.0

3.3
4.0
3.1
4.0
3.6
3.3
3.5
2.9
3.8
3.4
3.2
3.6
3.0
4.2
3.4

-

-

-

-

-

-

-

-

-

-

-

-

7.0

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5. GASOLINE VERSUS DIESEL FUEL VEHICLES
IN THE ARIZONA TRAFFIC POPULATION

METHODOLOGY
The analysis of fuel t y p e usage by vehicle distributions concentrated on three
major vehicle types. They were:
o L i g h t d u t y vehicles (typically passenger cars).
o

Light d u t y t r u c k s (truck-type vehicles having gross vehicle weights of 8,500
pounds o r less).

o

Heavy duty vehicles (truck-type vehicles having gross vehicle weights
g r e a t e r t h a n 8,500 pounds).

I t should b e noted t h a t t h e s e classes a r e comparable t o t h e ADOT vehicle
classification s c h e m e s defined earlier, i.e., light duty vehicles consist of all autotype vehicles, light duty trucks r e l a t e t o the light truck class, and heavy duty
vehicles c o m p r i s e t h e medium a n d heavy duty truck classes.
Comparisons of r e c e n t (7/13/86) Arizona vehicle registration d a t a were
conducted to d e t e r m i n e t h e p e r c e n t a g e of gasoline fuel versus diesel fuel type usage
between vehicle classes.

A similar comparison f o r validation purposes was

conducted on 1985 (6/30/85) Arizona registration statistics. Table 7 summarizes the comparisons.
CON CL US1ONS
The findings indicate t h a t Jow percentages of diesel fuel use exist among light
duty vehicles a n d light duty trucks. Approximately 1.50 t o 2.00 percent of vehicles
registered i n Arizona in t h e s e classes a r e diesel fuel users. T h e i m p a c t of this small
p e r c e n t a g e of diesel fuel users o n t h e fuel efficiency (mpg) characteristics of these
vehicle c l a s s e s would be e x p e c t e d t o b e statistically insignificant and, therefore,
may b e e x e m p t e d f r o m use in t h e VMT model calculations.
However, f o r t h e heavy d u t y vehicles (comprising t h e medium and heavy duty
truck types), diesel f u e l use i s significant. S t a t e w i d e 1986 registration d a t a
indicates t h a t o v e r one-third of t h e vehicles in this class a r e diesel fuel users. While

t h e vehicle r e g i s t r a t i o n data d o e s n o t readily s e p a r a t e diesel use by medium-duty or
heavy-duty t r u c k , a similar p e r c e n t a g e mix (diesel vs. gasoline) i s proposed f o r both

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For model purposes, a two-thirds "gasoline" and one-third "diesel1' fuel use

percentage split is proposed.

As annual figures a r e avaiIable from the Motor

Vehicles Division, t h i s split should be checked and revised a s necessary.

Table 7
DIESEL VERSUS GASOLlNE FUEL TYPE USAGE
AMONG ARIZONA-REGISTERED VEHICLES

Vehicle
Type

P l a c e of
Registration

Light Duty
Vehicles

Maricopa
County
Pima
County
Yuma
County
Statewide

t i g h t Duty
Trucks

Maricopa
County
Pima
County
Yuma
County
Statewide

Heavy Duty Maricopa
Vehicles
County
Pima
County
Yuma
County
Statewide

Total
Vehicles

DieselUse
Vehicles

Sb

Diesel

Total
Vehicles

DieselO/b
Use
Vehicles Diesel

-

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6. ADOPTION OF MPC FACTORS
METHODOLOGY

The analysis of t h i s issue included a l i t e r a t u r e review of various sources of
fuel efficiency (mpg) d a t a f o r t h e vehicle classes described in t h e earlier portions of
this report.

In addition, adjustment f a c t o r s t o r e f l e c t environmental impacts,

vehicle type and age, driving habits (urban vs. rural), and o t h e r a r e a s were
researched t o fully identify reliable base 'Irnpg'' estimates.

CONCLUSIONS
The analysis of this issue resulted in the following key conclusions:
o

The key source of base "mpg" d a t a for passenger vehicles (autos) i s d a t a
published annually by t h e EPA. These d a t a a r e based primariiy on new
vehicle testing. Adjustment f a c t o r s f o r vehicle population a g e , on-road use
(urban vs. rural driving percentage), a n d regional/seasonal type i m p a c t s
have been developed in key research e f f o r t s conducted over t h e years.

o

T h e key source of base "mpg" d a t a for t h e t r u c k classifications (i.e., light,
medium, and heavy) i s d a t a published by United S t a t e s D e p a r t m e n t of
:
inventory and
C o m m e r c e in i t s annual c e n s u s of ~ r a n s ~ o r t a t i o nTruck
Use Survey. D a t a a r e available on a national and individual s t a t e basis and
is supplied by t h e trucking industry as a requisite f o r highway user t a x
purposes. T h e d a t a i s essentially pro-rated based on fuel efficiency ranges.
T h e use of individual state-registered d a t a limits t h e regional/seasonal
a d j u s t m e n t needs. Furthermore, t h e d a t a a c c o u n t s f o r ~ n - ~ o ausage
d
and
vehicle a g e considerations.
F o r use in t h e V M T model, "mpg"
c h a r a c t e r i s t i c s a r e similar for Arizona-registered t r u c k s and n o n - ~ r i z o n a
r e g i s t e r e d t r u c k s travelling within t h e S t a t e .

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a

usocirtcs

7. REFERENCES
1.

Matthias,.3.S. and A.G. Dean, "Vehicle Classification Procedure Study," Arizona
Department o f Transportation Report No. FHWAIAZ-841195, I, Final Report,
June, 1984

2.

Highway Statistics 1984, USDOT, FH WA, Washington, D.C., 1985.