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OCR for page 31
31
Chapler Five
SATURATION HEADWAYS
IMPORTANCE OF SATURATION HEADWAYS
The basic parameter used to compute intersection capacity
is saturation headway. For signalized intersections, ideal
saturation headway is the difference in the passage time
at the intersection stop line between two consecutive
vehicles once the queue is moving in a stable manner. The
1985 Highway Capacity Manual (HCM) notes that the
saturation headway is "estimated as the constant average
headway between vehicles which occurs after the fourth
vehicle In the queue and continues until the last vehicle In
the queue clears Hat intersection." Field measurements
must consider the start up lost time, or that time at He
beginning of He green phase Hat is required for the queue
to begin to move. The capacity procedures given
Chapter Nine of the HCM (Signalized Intersections)
provide a standard value for the ideal saturation headway
of 1.9 seconds per vehicle, which yields an ideal saturation
flow rate of 1900 vehicles per hour of green. The
procedure provides adjustments to this ideal value to
consider the effects of intersection geometry, opposing
traffic Bow, signal liming parameters, and pedestrian
Bows.
For TWSC intersections, Me folZow~up fume, or lbe time
headway between the second and following vehicles
entenngirom a continuous queue Ante minor stream and
utilizing He same major stream gap, is equivalent to the
saturation headway. FoDow-up time values published In
the 1994 update to the HCM range from 2.1 seconds for
major street left turn vehicles to 3.4 seconds for minor
street left turn vehicles. Recommended values from this
current study range from 2.2 seconds to 3.5 seconds for
these same vehicle movements.
For AWSC intersections, the saturation headway is the
time headway between two vehicles departing from the
same lane under conditions of continuous queueig.
Saturation headway is used to compute capacity In both He
1985 HCM and the 1994 HCM update. Saturation
headway is also one of the primary input parameters
marred for He proposed capacity procedure descnbed in
chapter three of this report
RESEARC:EI HYPOTHESES: FACTORS
AFFECTING SATURATION HEADWAYS
Past studies and close observation of traffic operations as
part of this study provide evidence that the saturation
headway for a vehicle at an AWSC intersection is a
function of both traffic flow characteristics as weD as
intersection geometry. Since the saturation headway is
the key parameter to be used in the estimation of He
approach capacity, it is important to understand and
quantify the factors that affect it. Based on previous
work, eight degree of conflict cases are assumed to be
necessary to completely describe He conditions faced by
a driver at the stop line of an AWSC intersection.
Four hypotheses are proposed and evaluated.
Hypothesis ~
The saturation headway of a subject vehicle is dependent
upon the degree of conflict faced by He subject driver as
measured by the presence of vehicles on the opposing and
conflicting approaches.
la. The saturation headway for case 2 is larger Can
for case I.
Ib. The saturation headways for case 3 and case 4
are the same and bode are larger than He values
for case 2.
Ic. The saturation headways for cases 5, 6, and 7
are the same and are all larger than He values
for cases 3 and 4.
Id. The saturation headway for case ~ is larger An
the values for cases 5, 6, and 7.
Hypothesis 2
The saturation headway of the subject vehicle is
dependent on intersection geometry, particularly the
number of lanes on the conflicting approaches, He
opposing approach, and the subject approach.
2a. The saturation headways for Group ~ sites are
less than He values for Group 2 sites.
The saturation headways for Groups 3 and 4
sites are not significanfdy different, are greater
then the values for Groups ~ and 2, and are less
than the values for Groups 5 and 6.
OCR for page 32
32
2c. The saturation headways for Group 5 are greater
than the values for Groups ~ Trough 4 and are
less Man for Group 6.
20. The saturation headway for Group 6 are greater
than the values for Groups 2 through 5.
Hypothesis 3
The saturation headway of the subject vehicle is
dependent on in directional movement as wed as the
directional movement of the opposing and conflicting
vehicles.
3a. The saturation headway for left turn vehicles is
greater than He value for Trough vehicles.
3b. The saturation headway for left turn vehicles is
greater than He value for right turn vehicles.
3c. The saturation headway for Trough vehicles is
greater than the value for right turn vehicles.
34. The specific interactive combinations of the
subject, opposing, and conflicting vehicles affect
He saturation headway. Or, the greater He
conflict between movements, the higher the
saturation headway is likely to be.
Hypothesis 4
The saturation headway of He subject vehicle is
dependent upon its vehicle type.
4a. The samradon headway for passenger cars is less
than for heavy vehicles.
These hypotheses are tested In two ways. First,
difference of means tests are conducted using the sample
means, sample variances, and sample sizes from the
samples being compared. The z-statistic is evaluated at
the 0.01 significance level In each case. Second,
regression equations are developed to help assess Be
quantitative effects of these factors.
HYPOTHESIS TESTIN~GROIJP 1 SITES
Analysis of Eight Degree of Conflict Cases
It was ~n~dady proposed Hat eight degree of conflict cases
are required to Filly descnbe the conditions faced by the
subject approach driver. These cases are described
Table 35.
Table 35. Headway Cases
Table 36 shows the mean headway, standard deviation,
and number of observations for each of the eight degree-
of Conflict cases for the single lane (Group I) sites. The
mean and plus/minus one standard deviation range are
Gown In Figure 9.
Table 36. Saturation Headways, Single Lane Approach Sites
3.86
4.78
S.8g
S.89
7.42
7.34
7.3S
9.SO
1.38
t.S6
i.70
i.67
1.95
2.~!
2.09
2.92
385S
te74
1073
934
s72
572
S55
427
The data presented Table 36 and in Figure 9 suggest that
separate headway cases should be maintained for case I,
case 2, and case S. However, He data suggest Cat cases 3
and 4 and cases 5, 6 and 7 might be combined. Difference
of means tests were completed to determine statistically if
the hypotheses la through le can be supported.
Table 37 shows the results of these tests.
OCR for page 33
33
Table 37. Hypothesis Tests: Consolidation of Headway Cases
Stan
Headway Case
Mean
Vanance
Observations
.
Z Test Results
Computed z value
PI =z) one-tail
z Cntical one-tail
P(T < =z) tw~tai1
z Cntical tw~tail
ID _
3.86
1.90
3855
2
4.78
2.43
1874
-21.68
0.00
2.33
0.00
2.58
Reiect
3
5.88
2.89
1073
4
5.89
2.79
934
4.15
0.44
2.33
0.22
2.58
Accent
2
4.78
2.43
1874
5.88
2.89
1073
-17.39
0.00
2.33
0.00
2.58
Re ect
J
Table 38. Hypothesis Tests: Consolidation of Headway Cases
Stan
Headway Case
Mean
Vanance
Observations
Z Test Results
Computed z value
P(Z<=z) one-tail
z Cntical one-tail
P(Z< =Z) tw~tail
z Critical tw~tail
Ho: Cases ale identi=1
3 4 5 6 5
5.88 5.89 7.42 7.34 7.42
2.89 2.79 3.80 4.45 3.80
1073 934 572 572 572
.15
0.44
2.33
0.22
2.58
Accept
0.65
0.26
2.33
0.13
2.58
Accept
7
7.35
4.37
555
6
7.34
4.45
572
7.35
4.37
555
7.35
4.37
555
8
9.50
8.53
427
' 1 ' 1 ' 1
0.59
0.28
2.33
0.14
2.58
Accept
-0.06
0.48
2.33
0.24
2.58
Accept
-12.91
0.00
2.33
0.00
2.58
Reiect
AWSC- Single Lane Sifes
15
~0
5
o
i:
........... ........... = =
1
2 3 4 5
Case
6 7 8
Figure 9. Mean Values and Plus/Minus One Standard Deviation
Saturation Headway Values
Three major conclusions can be drawn from Table 38:
.
.
There is statistical evidence that headway cases 3
and4 can tee combinedinto one case. This means
that the direction of approach of a vehicle on the
conflicting approach does not significantly affect
the saturation headway of the subject approach
vehicle.
There is statistical evidence that headway cases 5,
6, and 7 can be combined into one case. This
means that when faced with two vehicles on Me
opposing and conflicting approaches, the direction
of approach is not significant.
Cases I, 2, and g should remain as separate cases.
The combined cases are shown in Table 39. Note: From
OCR for page 34
34
this point on in this report, the degree of conflict cases
wiR be designated from ~ to 5, according to the results
presented In this section of the report.
Table 39. Saturation Headway Dam for each Case
3.86
4.78
S.88
7.37
g so
1~8
1.S6
1.69
2.0S
2 92
38SS
1874
2007
1699
427
Note: StDev is He standard deviation Obs is the number of observations.
Figure 10 shows Me frequency distribution for the
saturation headway measurements for each degree of
conflict case. Figure 10 shows that the more complex the
degree of conflict,` the higher the mean value of
saturation headway and the hither the vanability about
Me mean, bow important conclusions. Note also that Me
headway dis ribudons are not normal, but have a definite
skew to Me right.
The variation of Me mean value of Me saburabon
headway at each site for each of Me new degree~f-
conBict cases is shown in Figures I} Trough 15. These
figures illustrate a high level of agreement (relatively low
vanadon) between the measurM values at each site. Also
shown in Me figures are the confuted capacities (3600
divided by Me samradon headway3 for each site.
0.10
~ .
=0.05
0.00
. ~-,`.
0 5 f0 15 20
Satumffon Headway
| |-N1--N2- N3--N4--NS| l
Figure 10. Frequency Distributions for Degree of Conflict Cases
15
^10
S
O
Saturation Headways, Case
Single Lane Sites
Site
~ H - dwarfs Capacity
1200
800
400
. -o
Figure 11. Variation of Saturation Headway and Capacity by Site,
Saturation Headways, Case 2
Sing/e Lane Sites
15
,4 10
:c 5-
O - ~,EN,~,~I,t~,~3,~,tNI~,~,~I~l O
Site
Headway Capacity
- 1200
...........................................................................
...........................................................................
800
400
Figure 12. Variation of Satumbon Headway and Capacity by Site,
15
~10
s 5
O
Saturation Headways, Case 3
Sing/e Lane Sites
~3 Headword Capacity
1200
800
400
O
Figure 13. Variation of Saturation Headway and Capacity by Site,
Case 3
OCR for page 35
15
,...
~ .
.
+
l ~
Site
Headway Capacity
120lv
800
-400
-O
| ~ Headword Capacity
Are 14. Variation of Saturation Headway and Capacity
e4
Saturation Heac~ways, Case
tSingle Lane Sites
15 , .
~0
~ ~.~.~.~..~.~.~.~.......
.
.... ~
. . .
I.'
....
id,
....
. _
:
. . .
- -I--- ~1- ~ - T _ ~ ~ ~ ~ ~
Site
Headway Capacity
1200
800
400
O
~ 15. Variation of Saturation Headway and Capacity by Site,
Case 5
.. ...
Table 41. Headway Case 1-Turning Movement Difference in Means Tests
Effect of Directional Movement. Table 40
Case 1
Mean
Variance
Ob~ons
3.92
2.S6
367
3.92
1.74
3063
3.35
2.31
425
Case 2
Mean
Variance
Ob~ons
S.S9
2.69
197
4.72
2.28
14S6
4.45
2.62
221
Case 3
Mean
Variance
Ob~ons
6.02
2.92
341
S.97
2.66
1373
S.32
3.31
293
Case 4
Mean
Variance
Observations
8.00
S.11
32S
7.34
3.84
1148
6.63
3.65
226
Case 5
Me"
Variance
Observations
9.94
7.84
106
9.31
6.45
270
9.58
20.70
S1
The difference in means tests for directional movement
of Me subject vehicle are summarized in Tables 41
through 45.
.^ ,
.. 4 ..~. ...
1'
t:.:-::--:::::-:.:-:-:-:::.:::::-:::::.::-::::::::::::::::::::::::: :::::::::::: :::::-::: :::-::::::-:-:-:-: ::-::
E:::::::::::::::::: -:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::- :::::::::::::::::: :::::::::::: ::::::::::::::: -:::::.:.- :.:.:::.:::.:::.:. -:::::::::::::::::::::::::::
Ista~cs I I T T I 1~
T=g Movement LT ~111
Me" 3.92 1 3.92
Variance 2.S6 1 L74
Observations 367 1 3063
Z Test Results
Computed z value -0.04
P(Z<=z) one-tail 0.49
z Critical one-tail 2.33
P(Z<=z) ~v~tai1 0.24
z Craft ~~1 2.Sg
Ho: Cases are identical Accent
LT
3.92
2.S6
367
S.1S
0.00 1
2.33 1
Coo 1
2.S8
Reject |
RT
3.3S
2.31
42S
TH
3.92
1.74
3063
7.44
0.00
2.33
0.00
2.Sg
| Reject
RT
3.3S
2.31
42S
OCR for page 36
36
Table 42. Headway Case 2-Turning Movement Difference in Means Tests
alel~ ler 1 ' ''""""'' '~"' "" ''''""'''''' 'I' '' '''' '' ' ' ' ' ''' ''''' '' ''''''] - -
s~C5 T T T I T I L
Turning Movement LT TH LT RT TH
Mean S.S9 4.72 S.S9 4.4S ~4.72
Vanance 2.69 2.28 2.69 2.62 2.28
Observations 19 7 1 4S 6 19 7 2 2 1 14 S 6
Z Test Results
Computed z value 7.08 7.11
P(Z<=z) one-tail 0.00 0.00
z Critical one-tail 2.33 2.33
P(Z<=z) two-tail 0.00 0.00
z Critical two-tail 2.S8 2.S8
H0: Cases are identical Reject ReJect
RT
4.45
2.62
221
2.27
0.01
2.33
0.01
2.Sg
tccept
Table 43. Headway Case 3-Turning Movement Difference in Means Tests
... , ,
...........................................................
Staffsffcs
Tuming Movement LT TH LT RT TH
Mean 6.02 S.97 6.02 S.32 S.97
Variance 2.92 2.66 2.92 3.31 2.66
Observations 341 1373 341 293 1373
Z Test Results
Computed z value 0.S6 4.96
P(Z<=z) one-tail 0.29 0.00
z Cntical one-tail 2.33 2.33
P(Z<=z) two-tail 0.14 0.00
z Critical two-tail 2.SS 2.S8
H0: Cases are identical Accept R~ect ~-
Table 44. Headway Case 4-Turning Movement Difference in Means Tests
TH
7.34
3.84
1148
RT
S.32
3.31
293
S.57
0.00
2.33
0.00
2.Sg
Reject
P :::: '''-'' '''''''' ''' :$ ~
Stadstics 1 1 1 1 1 1
Tuming Movement LT TH LT RT ~
Mean 8.00 7.34 8.00 6.63 1
Variance S.11 3.84 S.11 3.6S
Obsenrations 32S 1148 32S 226
Z Test Results
Computed z value 4.83 7.68 ~
P(Z<=z) one-tail 0.00 0.00 |
z Cntical one-tail 2.33 2.33
p(z<=z)two tall 0.00 0.00
zC:riticaltwo-tail 2.S8 2.S8
H0: Cases are identical Reject R~ect
S.04
0.00
2.33
0.00
2.S8
Reject
RT
6.63
3.65
226
OCR for page 37
37
Table 45. Headway Case 5-Tuning Movement Difference in Means Tests
3 ....................................................................................
'"''' ''""''''''"'"''""'"'' ''''""" :' ''' , ~. ~, , ;
Staff~ffcs
Tu~ning Movement LT TH LT RT TH RT
Mean 9.94 9.31 9.31 9.S8 ~9.31 9.58
Variance 7.84 6.4S 6.4S 20.70 6.4S 20.70
1 )bservadons 1 106 1 270 1 270 1 51 1 70 1 51
l | ' Test Results l
Computed z value 2.00 -0.40 -0.40
P(Z<~) one-tail 0.02 0.34 0.34
z Critical one-tail 2.33 2.33 2.33
P(Z<=z) two-tail 0.01 0.17 0.17
z Critical two-ta~1 2.S8 2.S8 2.Sg
HO: Cases are identical Accept Accept Accept
The results of the difference in means test are
summarized in Table 46. These tests support, for Me
most part, hypotheses 3a, 3b, and 3c, that the directional
movement affects saturation headway. Even for Pose
tests Tat do not support the hypotheses, We relative
values of Me saturation headways are as expected.
Table 46. Summary of Hypothesis Tests
; , ................ ................ .................. .................... :
:.~::~:~:::~:~:~:~:~:~: m::: :.:::: :::::::::::::: +.:.:.: :: :~:~:~.:::~:~: :.:: ::.:::::::::: ^:.::: :.:.: ^:~:~: :~: :~:::::::: :: ::::: all:::
:~ you-= ;t test; ~ ~ ~ · ~ ~ ~e ~-e e~ ~ ~ ~ - - -~90Ft ~· - ~e;;, .
., it. , . ,. ,. , , , .... ... , ..... ,
.
Test 3a(~1~111) N Y N Y N
Test 3b(Ll>RT) Y Y Y Y N
Test 3c(TH>RT) Y N Y Y N
Note: Y = supports hypothesis. N = does not support hypothesis.
,.
Effect of Heavy Vehicles. The saturation headway data
for each degree of conflict case are divided according to
the vehicle Me of the subject vehicle. These data are
shown in Table 47.
The results of Me difference in means test are given in
Table 48. In most cases, hypothesis test 4a is supported
by Me data. ~ aD cases, the mean values for passenger
cars are less than the mean values for light trucks or
heavy trucks.
OCR for page 38
38
Table 47. Saturation Headway by Vehicle Type
Passenger Car
Mean
Std Dev
Observations
3.8S
1.37
3814
4.77
1.SS
1849
S.86
1.6S
1984
7.3S
2.01
1664
9.49
2.90
419
Light Truck
Mean
Std Dev
Observations
5.S3
2.00
14
4.78
1.85
15
6.72
1.81
3
7.84
2.12
18
6.84
3.76
2
Heady Truck
Mean
Std Dev
Observations
S.S9
1.74
10
6.94
1.93
8.86
4.39
9
11.08
5.14
9
12.25
2.88
S
Motorcycle
Mean
Std lees
Observations
3.Sg
1.63
17
3.43
1.68
4
6.S0
1.94
11
6.90
0.93
g
7.42
N/A
1
Table 48. Hypothesis Tests. Vehicle Type
Mean
Mown Variance
Observations
I' 2;2'22 '' "' "' '' ':""'' "'"'"''I'' ''
~ '2 I"''"" "'" ''' ' ' ' ~ i.,. . ,~., , ,4 .. .... ,l ;,. . 1
T Trlc | PC | Trk | PC 7 Tlk | PC T Turk
S.55 4.7g 4.87 5.89 S.29 7.38 6.7S
3.31 2.41 4.33 2.73 lS.S6 4.03 13.48
24 1849 21 1984 12 1664 27
l ) t O C
4.S8 -1.36 -2.16 -2.23
0.00 0.09 0.02 0.01
2.33 2.33 2.33 2.33
0.00 0.04 0.01 0.01
2.S8 2.S8 2.S8 2.Sg
Re j ect Accept Accept Accept
PC
3.85
1.88
3814
Hypothesized Mean Difference
z
P(Z<=z) onedail
z Critical one-tail
P(Z<-z~tw~tail
z Critical two-tail
Conclusion: Cases are Identical
Not sufficient data
for hypotheses tests
Effect of Opposing and Conflicting Movements. It bus
already been shown that the directional movement of Me
subject vehicle affects its samraffon headway. To obtain
further insights on the effect of directional movement,
consideration was given to specific combinations of
subject, opposing, and conflicting movements.
AD nine movement combinations for case 2 are shown In
Table 49. Movement pairs that either cross or merge
have mean saturation headway values that range from
4.92 seconds to 6.29 seconds. The unweighted mean
value of these means is 5.8 seconds. Movement pairs
that do not cross or merge have saturation headway
values Mat range from 4.15 to 4.78 seconds. The
unweighted mean value for these means is 4.4 seconds.
These measurements confirm that the degree of conflict
between vehicles significantly affects saturation headway
values.
All 27 movement combinations for case 3 are shown in
OCR for page 39
OCR for page 41
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OCR for page 44
OCR for page 45
OCR for page 46
OCR for page 47
OCR for page 49
OCR for page 50
Representative terms from entire chapter:
saturation headways
39
Table 49. Movement pairs Mat either cross or merge
have saturation headway values that range from 5.5
seconds to 7.4 seconds, wad an unweighed mean of the
mean values of 6.3 seconds. Movement pairs Mat do not
cross or merge have saturation headway values that range
from 4.4 seconds to 5.7 seconds, with a mean of S.1
seconds. Again, these measurements confirm Me
importance of Me specific level of degree of conflict
between movements.
Selected topped for case 4 also show the effect of degree
of conflict. The two values with no conflicts are 5.3
seconds and 7.7 seconds. The two values wad conflicts
between aD three movements are 8.3 and 8.S seconds.
Figure 16 ~mmanzes these results for these three cases.
The x ems values in this figure are defined as follows.
The first number is the degree-of-conflict case. Y or N
denotes if a conflict between the movements excess ~ or
not (N).
Table 49. Saturation Headways for Various Conflicting Vehicle Movements for Group 1 Sites
1 ' 2 2 222 ' 22 'I''' - ' '1 '' ' ' ' I'' '"''""'' ' '' ;':~''1"'' " "' '''''''''''''' -1"''''* ' - " ' ' "' '' '
............... . . .. .. . . . ... . . . i . ... .. . . . . ~
| `~ 1 l ~ D CD~i~g ~DV~
Case2
All 4.78 1.S6 1M4
SLT~LT 4.92 1.76 19
SLOTH 5.70 1.61 lSO
SLT~RT 5.78 1.83 34
STILT 6.16 1.55 181
STEALTH 4.54 1.41 1165
STEWART 4.78 1.63 166
SRT~LT 6.29 1.30 30
SRT~TH 4.22 l.S1 168
SRT~ORT 4.1S 1.42 29
Case3
All S.88 1.69 2007
SLT~LLT S.72 1.3S 39
SLT
40
,,10
.' 5
co ..........
..........
0 2
Degree of ConRict
Figure 16. Effect of Turning Movement Conflict
Combinations on Saturation Headway
Table 50. Effect of Time in Queue on Saturation Headway
4.74
1.S7
S78
4.84
1.S3
S13
4.71
l.SO
217
4.77
1.37
82
4.47
1.70
42
4.26
1.40
29
Effect of Time in Queue. The effect of time in queue on
Be saturation headway was not listed earlier as a specific
hypothesis tom However, Me influence of time in queue
of the subject vehicle has been suggest to adversely
affect the critical gap and follow up time for TWSC
intersections. ~ addition, Were was some concern that
sites from this current sty with low volumes may result
In lower pressure on the subject approach Diver Bus
affecffng the comparability of saturation headway values
between sites. The data were divided according to the
time In queue of the subject approach vehicle. A review
of the dam presented in Table 50 does not support any
clear effect of Be time in queue on saturation headway.
This is probably because at AWSC intersections, drivers
are assured of getting through He mtersecdon; this
contrasts And TWSC Intersections where this assurance
is not guaranty.
'1 2 ~ 2' ' ' ' '' ' ''I $ ~' ' - ~: ' ' ' 1
~ Awe .................. .... ... ....... . .. .................. . .. ... . ...
. L]O I
Mean 3.80
StDev 1.36
Obs 1884
10-20
Mean 3.93
StDev 1.37
Obs 1011
20-30
Mean ;^ 3.9S
StDev 1.4S
Obs 483
3~40
Mean 4.02
StDev 1.31
Obs 2S0
40-50
Mean 4.03
StDev 1.15
Obs 136
>50
Mean
StDev
Obs
.:~:-.:.:.:-.-.:.:.:~:-.:.:-:.:-:~:~:.:-:.:.:.:~.:-~:~.:-.:~:~:.:.:.:.: ·.:.:.:::~:-.:.:.:-.:-:::-:-:::::-~--~.:~:-:-:.:.:~:~.:.:-~:-:-:.:.:-.:.
.:-.: :~:.:-:.--:~--.:.:.-.:::::: ~.:.:~:.:.--.:~.:-.-.:.:-:-:-:~:- . ~ ~ . ~.
S.96 7.36
1.73 2.04
1142 997
S.88 7.48
1.68 2.07
485 441
S.62 7.2S
1.44 2.21
221 161
S.78 7.0S
1.60 1.61
104 66
S.87 7.S9
1.60 2.32
39 26
S.22 6.84
0.91 1.28
14 8
9.36
2.S2
248
9.90
3.49
104
9~6.0
2;S7
4S
9.66
4.65
21
8.03
2.33
8
7.36
N/A
1
41
HYPOTHESIS TESTIN~GROUP 2, 3, AND 4 SITES
Group 2 Sites. Group 2 sites are those with single lanes
on both the subject and opposing approaches and two
lanes on one conflicting approach and one lane on He
over conflicting approach.
The saturation headways for the Group 2 sites are
compared to the values measured at the Group ~ sites
(single lanes on each approach) for comparable degree
of conflict cases. These values are shown in Table 51.
Hypothesis 2a proposed Hat He headways for Group ~
sites were less Man for Group 2 sites. The results of the
difference in means tests shown In Tables 52 and 53,
however, do not support this hypothesis in four of the
five cases tests. That is, He saturation headways for
Groups ~ and 2 sites are not stadstically different.
-
Table 52. Hypothesis Test 2 for Each Degree of Conflict Case
Sacs
Mean
Variance
Ions
Z Test Remlts
Computed z value
P(Z<=z) one-tail
z Critical one-tail
P(Z<~) To
z critical two-tail
HO: Cases are identical
Table S1. Headway Data for Groups 1 and 2 for Hypothesis 2a Tests
_~~~ _
Case 1
Mean 3.86 4.00
StDev 1.38 1.30
Obs 38SS 249
Case 2
Mean 4.78 S.S2
SUDev 1.S6 1.79
Obs 1874 60
Case 3
Mean S.88 S.70
SUDev 1.69 1.47
Obs 2007 349
Case 4
Mean 7.37 7.34
SUDev 2.05 1.62
Obs 1699 295
.
Case S
Mean 9.S0 9.31
StDev 2.92 2.61
Obs 427 142
... . ~'1''"''"': '''I'' ~ - ~; ;t
2'222' """'"' ""''I"""'''' ' '1'~""'-''1"'
4.00 3.86 S.S2 4.78 S.70 S.88
1.69 1.91 3.2 2.43 2.16 2.84
249 38SS 60 1874 349 2007
.~
1. 58 1 3~18 1 -2.04
0.06 0.00 0.02
2.33 2.33 2.33
0.03 0.00 0.01
2.S8 2.Sg 2.SS
Accept Rhea Accept
42
Table 53. Hypothesis Test 2 for Each Degree of Conflict Case
. ..,.,., ., ., ., ., ., ., . . . . . . ... . . . . . . . . . . . . . . . .. . .. . .. ........ . . . .... . . . . . . . . . . . . . . . ... . ... . ... ...... ..... . ~ ~ ~ .. ... .. . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . ....... ..
, 2 ;
Statistics
Mean
Variance
Ob~ons
7.34
2.62
29S
7.37
4.20
1699
9.31
6.81
142
ALSO
g.S2
427
Z Test Results
Confuted z value
P(Z<=z) one-tail
z Critical one-tail
P(Z<=z) tw~tail
z Critical tw~tail
HO: Cases are identical
-0.26
0.40
2.33
0.20
2.58
Accept
-0.74
0.23
2.33
0.11
2.S8
Accept
Group 3 Sites. Group 3 sites have one subject approach
lane, two opposing lanes, and either one or two
conflicting approach lanes. AR Group 3 sites are T-
intersections with two opposing approach lanes and only
one conflicting approach. Group 3a sites have one
conflicting approach lane; Group 3b sites have two
conflicting approach lanes.
Table 54 lists the saturation headways for Group 3,
Group 3a, and Group 3b, for four of the five degree of
conflict cases.
The number of observations permit difference in means
tests for degree of conflict cases ~ and 2 only. The
results of these tests are given in Table 54.
The first test determines if Me Group 3a and 3b sites
yield similar or different saturation headway values. For
degree of conflict cases ~ and 2, the saturation headway
values are sign~ficandy different showing that the number
of conflicting lanes affects the value of saturation
headway. This difference is likely due to the increased
distance traveled through the intersection. These are
listed as tests 5a and 5b.
Test 2a shows Tat We number of conflicting lanes does
not affect Me saturation headway.
Test 2b shows mixed results. Test 2b(~) shows Mat if
Mere are bow 2 lanes on the opposing and conflicting
approaches, Me saturation headway is greater Man for
single lane sites. Just adding a lane on Me opposing
approach, as shown in Test 2b(2), does not cause a
significant difference, however.
Table 54. Saturation Headways for Group 3
Case 1
Mean
Stand Dev
Observations
4.16
1.19
1707
4.13
1.18
1493
4.3S
1.20
214
Case 2
Mean
Stand Dev
Observations
4.7S
1.46
1226
4.71
1.42
1105
S.19
1.67
121
Case 3
Mean
Stand Dev
Observations
7.S2
2.63
12
6.22
1.47
202
Case 4
Mean
Stand Dev
Ob~v~ons
6.6S
1.05
7
7.35
2.15
212
Case 5
Mean
Stand Dev
Observations
ibis case not applicable for this geometric group.
43
Table 55. Hypo~esis Tests for Groups 1, 2, and 3
:~ ::::::::::::::::::::::::::':':':':':':':':': :':':':':':':':':':':':' ':': :::':':'::: :::::':::::::::::1 :::::::
.................................................................................................................................................... : ~ ;~
StaffsUcs 1 1 1 1 1 1
Geometric Group 1 2 1 3b 2 3a
Mean 3.86 4.01 3.86 4.3S 4.01 4.13
Vanance 1.91 1.63 1.91 1.4S 1.63 1.39
Obsavations 38SS 229 38SS 214 229 1493
_
Z T"t Remlts
Computed z value -1.71 -S.71 -1.32
P(Z<=z) one-tail 0.04 0.00 0.09
z Ckitical one-tail 2.33 2.33 2.33
P(Z<=z) two~ail 0.02 0.00 O.OS
z Critical two~ail 2.S8 2.S8 2.S8
HO: (~ are identi~t Accept Reject Ac~xpt
Table 56. Hypothesis Tests for Groups 1, 2, and 3
'tadstics - 1 1 1 1 1
Geometric Group 3a-NC1 3~NC1 3a-NC2 3~NC2
Mean 4.3S 4.13 S.19 4.71
Variance 1.4S 1.39 2.8 2.03
Observations 214 1493 121 llOS
Z Test Results
Con~uted z vatue 2.SO 3.04
P(Z<=z) one-tail 0.01 0.00
z C\itical one-tail 2.33 2.33
P(Z<=z) two~ail 0.00 0.00
z Criticaltwo-tail 2.Sg 2.SS
| HO: Cases are identical Reject Reject
Group 4 Sites. Group 4 ~ncludes sites w~th a s~ngle lane
on the subject approach, hvo lanes on the oppos~ng
approach, and ei~er one or two lanes on ~e conflictug
approaches. Stadshcal tesm ~ma~ in Tables 57,
58, and 59 show ~at the number of lanes on the
conflic~ng approaches sig~ficandy affects the samradon
headway.
Table 57. Saturabon Headway Data for Group 4 Sites
22 ~.~ ., , ,,,. .
.......................... , ......................................... ..............................................................................
1 3.72 .~.36 Regect
2 S.OS S.42 A~(ma~al)
3 S.60 6.17 Reject
4 7.19 7.77 R~ect
S 9.43 lO.S7 Reject
44
Table 58. Hypothesis Tests; for Group 4
. ~. ~................................................... -
~........ , ... , ., ,.~
Staff~ffcs
Geometric Group 4a 4b 4a 4b 4a 4b
Mean 3.72 4.36 S.0S S.42 S.60 6.17
Variance 2.18 2.2 2.9S 3.00 2.24 3.31
Observations 99 121 S2 132 208 376
Z Test Rests
Computed z value -3.16 -1.31 ~4.04
P(Z<=z) one-tail 0.00 0.10 0.00
z Critical one-tail 2.33 2.33 2.33
P(Z<=z) two-tail 0.00 0.0S 0.00
z Critical hro-tail 2.S8 2.S8 2.S8
He: Cases are identical Reject AT Reject
Table 59. Hypothesis Tests for Group 4
Staff - cs
Geometric Group 4a 4b 4a 4b
Mean 7.19 7.77 9.43 10.S7
Variance 2.96 4.13 S.3S lS.05
Observations 1 236 1 439 1 114 1 197
Z Test Results
Computed z value -3.92 -3.2S
P(Z<=z) one-tail 0.00 0.00
z Critical one-tail 2.33 2.33
P(Z<=z) tw~tail 0.00 0.00
z Critical tw~tail 2.S8 2.Sg
Ho: Cases are identical Reject Reject
HYPOTHESIS TESTIN~GROUP 5 AND 6 SITES
Group 5 Sites. Saturation headways for sites wad two
lards on He subject approach are given in Tables 60 and
61. Table 60 shows He six sites USA two lanes on each
of He four intersection approaches. Table 61 shows the
data combined for all sites wad two lanes on the subject
approach. These tables clearly show three points:
The saturation headway increases wad degree of
conflict.
The saturation headway increases as the number
of vehicles faced on the opposing and conflicting
approaches increases.
The variability of He saturation headway (as
shown by He standard denadon) also increases
as bow He degree of conflict and the number of
vehicles faced increases.
Group 6 Sites. Saturation headways for sites with three
lanes on each approach are given in Table 62. These data
clearly show three points:
I:
. .. .
~The saturation headway increases ninth degree of
conflict.
The saturation headway increases as the number
of vehicles faced on tile opposing and conflicting
approaches increases.
The vanabili~ of He saturation headway (as
shown by the standard deviation) also increases as
both the degree of conflict and the number of
vehicles faced increases.
45
Table 60. Saturation Headways, Group 5a Sites
...... a , ....... '''''' ''''" '' ' ' ""'"'"1
.... . , .
1 0 4.31 1.S3 S38
2 1 4.93 1.71 497
2 2+ 6.37 2.19 12S
3 1 6.44 1.91 609
3 2+ 7.00 1.90 76
4 2 7.13 1.87 1432
4 3 7.86 2.0S S86
4 4+ 8.87 2.SS 147
5 3 8.08 1.79 684
S 4 8.76 2.10 474
S 5 9.87 2.32 189
l S 6+ 10.87 3.24 81
Notes: Case is He degree of conflict case. NumVeh is Be number of
opposing and conflicting vehicles faced by He subject driver.
Table 61. Saturation Headways, All Group 5 Sites
................ ................. ............ ............
.. . ~............ ........ .......................... ........................
............................................ , . ~,.,. . ~.......................................... ...........................................
_ 0 4.32 1.49 781
2 1 5.01 1.69 6S7
2 2 6.27 2.1S 1S8
3 1 6.41 1.81 867
3 2 7.09 2.13 98
4 2 7.22 1.86 179S
4 3 7.98 2.07 717
4 4 9.16 2.73 167
S 3 8.32 1.87 81S
S 4 9.09 2.44 S49
S S 10.14 2.S2 229
1 S 6 11.63 4.88 100
Notes: Case is He degree of conflict case. Num~eh is He number of
opposing and conflicting vehicles faced by the subject driver.
Table 62. Saturation Headways, Group 6 Sites
... ,2. ~, '.2,2.'. - .,§ ~
1 0 4.45 1.S6 170
2 1 6.17 1.73 49
2 2 7.04 1.76 20
2 3 7.S1 1.6S S
3 1 6.81 1.38 146
3 2 7.47 1.86 46
3 3 ~7.94 2.02 11
4 2 8.26 1.81 96
4 3 8.78 1.72 48
4 4 9.70 1.92 32
4 S-8 12.S1 3.39 12
S 3 10.23 1.81 IS
S 4 11.32 2.27 14
S S 11.6S 1.97 S
S 6-9 13.43 3.01 14
Notes: Case is He degree of conflict case. NumVeh is He number of opposing
and conflicting vehicles faced by He subject driver.
REGRESSION ANALYSIS-GROllPS 14 SITES
The analysis presented ~ the previous sections showed
that the most significant factors affecting saturation
headway were the mining movement of the subject vehicle,
the degree of conflict fat by the subject vehicle, the
vehicle type, and the geometry of the intersection.
Regression analysis was used to determine ache effect of
each of these variables collectively on saturation headway.
The results of the analysis are presented In Table 63.
Single lane sites are designated Group I. Group 2 sites
have one lane on the opposing approach and two lanes on
either of the conflicting approaches. Group 3 sites (T-
intersections) have two lanes on the opposing approach
and either one or two lanes on the conflicting approaches.
Group 4 sites have at least two lanes on the opposing
approaches and one or two lanes on the conflicting
approaches. The details of the geometry of each site were
given earlier in this report in Table 25.
The constant term In each of the seven models presented
represents the ideal situation, the saturation headway for
passenger cars traveling straight through a single lane
approach intersection with no opposing or conflicting
vehicles at the intersection. When Group ~ sites are
included in Me analysis, this base case saturation headway
varies Tom 3.~S seconds to 3.93 seconds. This low
variation indicates that this is a very stable value and can
be used with confidence as a base value Dom which to
compute other saturation headway values. AD constant
terms are statistically different than zero.
The effect of the turning movement is clearly indicated in
the table. The sa~rabon headway for left turning vehicles
is higher than for a Trough vehicle by 0.23 to 0.34
seconds. The saturation headway for right turning vehicles
is less than for a through vehicle by 0.52 to 0.57 seconds.
Bow sets of values are statistically significant.
The saturation headway for heavy vehicles is higher than
for passenger cars by 1.41 to 1.65 seconds.
46
The degree of conflict with opposing and conflicting
vehicles affects the saturation headway. For case 2, the
increase is from 0.84 to 0.91 seconds. For case 5, the
increase is from 5.57 to 5.65 seconds. AD values are
statistic ally s ignif~c ant.
The effect of geometry is significant, and is particularly
dependent on the number of conflicting lanes. For T-
~ntersections, increasing the number of opposing lanes
Table 63. Regression Models for Saturation Headway Groups 1~ Sites
Bom one to two increases the saturation headway by 0.12
seconds. Increasing the number of conflicting lanes Mom
one to two increases the saturation headway by 0.42
seconds. For 4-leg intersections, increasing only the
number of opposing^lanes from one to two does not
significantly increase the saturation headway. But
increasing the number of conflicting lanes, if the number
of opposing lanes increases from one to two, does increase
the saturation headway by 0.56 to 0.57 seconds.
. ~ --; .. ......... I . ~
.............. ... ........... . ~.... . ~, ~. ....
...... .......... .
9,862 10,957 16,415 16,41S
0.668 0.676 0.688 0.6gS
0.446 0.457 0.473 0.473
0.446 0.457 0.473 0.473
1.716 1.716 1.703 1.703
~'"''"''l.2 ."..'"2""1''''" ~ ~
, , .. , ., ~ ..... ~
. .
0~( ~1 3.88 I 0. 3 1 3.90 1 0 O ~1 3.93 1 0.02
O.OS 0.26 0.05 0.24 0.04 0.23 0.04
0.05 -0.52 0.05 -0.55 0.05 -O.S7 0.05
0.19 1.41 0.19 1.65 0.14 1.64 0.14
O.OS 0.93 0.05 0.84 0.04 0.8S 0.04
0.06 1.94 O.OS 1.88 0.04 l.gS 0.04
0.04 3.01 0.04 3.06 0.04 3.03 0.04
0.09 S.57 0.08 S.6S 0.06 S.63 0.06
0.12 0.04
0.42 0.07 0.40 0.07
0.00 0.07
. O.S7 O.OS ' O.S6 0 OS
Observations
16,41S
R
R squared
add R squared
SEE
0.688
0.473
0.473
1.702
cot
LT
RT
TRK
Case2
Cases
Case4
CaseS
Group3A
Group3B
Group4A
Gioup4B
3.88
0.34
-0.S4
1.44
0.91
2.02
2.96
S.S8
3.90
0.24
-O.SS
1.6S
0.84
1.88
3.06
S.6S
0.12
0.42
O.S7
0.03
0.04
0.05
0.14
0.04
0.04
0.04
0.06
0.04
0.07
_ O.OS l
Notes: Colitis the regression coefficient, ~ ~ the standard error of Me coefficient estimate. ~ is the Standard error ofthe dependent vanable, Marion
headway.
47
REGRESSION ANALYSI~GROUPS 5 AND 6 SITES
The its of the regression analysis for sites with two or
more lanes on the subject approach is given in Table 64.
The base saturation headway (the constant in the
regression equation) representing passenger cars traveling
through the intersection facing no opposing or conflicting
vehicles is nearly the same for Group 5 (4.33 see) and
Group 6 (4.26 sect sites. These values are about 0.4
seconds higher than for the Group ~ sites, reflecting the
additional time required to travel through a multi-lane site.
The more complex the degree of conflict, the higher the
saturation headway. The terms for the venous degree of
conflict cases reflect this.
Table 64. Regression Models for Saturation Headways~roups 5 and 6 Sites
The saturation headway for heavy vehicles is I.6 seconds
higher than for passenger cars, for the Group 5 sites.
There were not sufficient heavy vehicles In the Group 6
Ma for a s~isticaDy-signiiicant estimate of this factor to
be made.
The saturation headway for left turn vehicles was 0.4 to
0.5 seconds higher than for passenger cars. For Group 5
sites, the saturation headway for right turning vehicles was
0.7 seconds less than for through passenger cars. No
estimate could be made for Group 6 sites, since there were
no right mining vehicles during penods of continuous
queueing at these sites.
.. ...... . ......
...................................................................... .................................................
..............................................................
........................................................................................................ .................................................................................. ..................................................
Observati news 1 5438 1 1495 1 6933 ~683 1 683 1
R | 0.63 1 0.74 1 0.64 | 0.78 | 0.78 |
R squared 0.40 O.S4 0.41 0.61 0.61
adjusted R squared 0.40 O.S4 0.41 0.61 0.60
SEE 1.90 2.0S 1.98 1.74 1.74 l
~< 1 65 ~1 1 ;
.
Constant 4.34 0.08 4.32 0.14 4.33 0.07 4.26 O.1S 4.26
LT O.S4 0.07 0.39 0.13 O.S4 0.06 0.42 0.14 0.42
RT -1.01 0.12 ~.37 0.17 -0.71 0.10 0.00 0.00 0.00 l
Tmck 137 0.19 3.00 0.4S 1.61 0.18 0.30 0.80
Case 2-1 0.61 0.12 0.88 0.21 0.66 0.10 1.73 0.28 1.73 0.28
Case 2-2 2.03 ^0.19 1.50 ~p.38 41.91 0.17 2.S7 0.41 2.Sg 0.41
Case 2-3 3.17 0.79 3.17 0.79
Case 3-1 2.07 0.11 l.9S 0.18 2.03 0.10 2.37 0.20 2.37 0.20
Case 3-2 2.82 0.23 3.12 0.46 2.85 0.21 3.0S 0.29 3.06 0.29
Case 3-3 3.S2 O.S4 3.S2 O.S4
Case 4-2 2.70 0.10 3.16 0.17 2.79 0.09 3.82 0.22 3.82 0.22
Case 4-3 3.39 0.11 4.0S 0.22 3.S1 0.10 4.40 0.28 4.40 0.28
Case 4-4 4.38 0.18 6.87 0.48 4.66 0.17 S.31 0.34 S.32 034
Case 4-S 8.07 O.S2 8.07 O.S2
Case S-3 3.60 0.11 S.09 0.23 3.83 0.10 S.74 0.47 S.74 0.47
Case S-4 4.28 0.12 6.7S 0.27 4.61 0.11 6.84 0.48 6.84 0.48
Case S-S S.40 0.16 6.93 0.3S S.67 O.1S 7.13 0.79 7.13 0.79
l Case Sat 6.38 0.23 10.37 0.49 7.1S 0.21 8.97 0.49 8.97 0.48
0.1S
0.14
nnn
Notes: Co
48
BINDINGS AND RECOMMENDED VALUES
This section of He report describes the analysis of
saturation headway values for AWSC intersections, and
the factors Hat affect these values.
Otis ~nteresdng first to compare the results from this study
with previous studies cited earlier in this report Table 65
shows these data for single lane (Group I) sites. While
some of the specific values vary, the trend of increasing
saturation headway values as the degree of convict
increases is consistent for ad studies.
Fable 65. Comparison Win Previous Studies of Saturation Headways
,
. ~e : :
1 ~1 4.0 1 3.9 I 1 3.21 3.0 1 3.9 1 3.9 :
2 ~2 1 5.6 I T 491 48 T 4-8 1 4.8 3
3 1 ~l 1 5.1 1 1 5.9 T 5-9 1 :
3 S.9
4 S.6 S.6 S.9
51 7.6 1 6.5 1 6.8 ~6.3 :71174
:
6 4 6.9 7.2 7.4 7.4
6.8 ~1 73 1 74 1 j1
8 1 5 1 9.0 1 8~4 T 8~0 T 95 1 95 1 95]
Four hypotheses were proposed. The hypotheses are
rest here and He findings and conclusions with respect
to ache hypotheses are presented.
Hypothesis ~
The saturation headway of a subject vehicle is dependent
upon the;de~ee of conflict faced by the subject driver as
meas~bytihe presence of vehicles on the opposing and
conflicting approaches.
Finding. The analysis of 12 single lane sites, including
date bom45 separate approaches, shows that five separate
cases are required to descnbe the degree of conflict
experienced by a subject approach driver. These five cases
are s~isticaDy distinct, forming a hierarchy of increasing
values of saturation headway as the degree of conflict
increases. This conclusion is support by both difference
in means tests and regression analysis.
Conclusion. This finding supports hypothesis I, including
ad of the sub-hypo~eses la, Ib, Ic, and Id.
Hypothesis 2
The saturation headway of the subject vehicle is dependent
on intersection geometry, particularly He number of lanes
on the conflicting approaches, the opposing approach, and
the subject approach.
Finding Creasing the number of lanes on the conings
approaches, while maintaining a single lane on~the
opposing approach does not significantly increase the
saturation headway of the subject approach driver. This
finding is based on a comparison of the five Group 2 sites
untie the twelve Group ~ sites. It should be pointed out,
however, Hat four of the five Group 2 sites had one lane
on one conflicting approach and two lanes on the other
conflicting approach, while one of the five sites had two
lanes on both convicting approaches. It may be argued
that two lanes on bow conflicting approaches for all sites
would have resulted in a statistically significant difference
between Group ~ and Group 2 sites, due to the increased
have! distance for through vehicles and a greater potential
for conflict between vehicles. This elect, however, was
not found in the analysis. This finding is supported by
bow difference in means tests and regression analysis.
49
Finding. Increasing the number of lanes on both the
opposing and conflicting approaches increases the
saturation headway of the subject approach vehicle. The
analysis shows that there Is a significant difference
between He headways measured at Group ~ sites and
Group 3 and 4 sites.
Finding Increasing the number of lanes on the subject,
opposing, and conflicting approaches, as well as the
number of vehicles on these approaches, increases the
saturation headway of the subject approach vehicle. This
finding is supported by regression analysis of Group 5 and
Group 6 site data.
Conclusion. These findings support Hypothesis 2.
Hypothesis 3
The sa~rabon headway of the subject vehicle is dependent
on its directional movement as well as the directional
movement of He opposing and conflicting vehicles.
Finding. The analysis of the data from the single lane
approach sites show that the saturation headway of the
subject approach Giver is affected by his or her directional
movement This conclusion is based on both difference in
means test and regression analysis.
Finding The same analysis shows thatch saturation
headway of He subject approach driver is affected by He
specific combination of He directional movements of the
subject, opposing, and conflicting approach vehicle. This
finding is supported by a comparison of the saturation
headway values for venous movement interaction
combinations.
Conclusion. These findings support Hypothesis 3, as well
as the sub-hypo~eses 3a, 3b, 3c, and 3d.
Hypothesis 4
The saturation headway ofthe subject vehicle is dependent
on its vehicle type.
Finding The analysis of the data for He single lane
approach sites shows Hat the saturation headway of the
subject approach Giver is a~ectedby the type of vehicle.
This finding is supported by both difference In means test
and regression analysis.
Conclusion. This finding supports Hypothesis 4,
particularly sub-hypothesis 4a.
Table 66 shows the resulting saturation headway values
for each geometry group and degree of conflict case, as
well as adjustments for boning movement and vehicle
type. Shaded ceils Ante table indicate parameters that are
not applicable for a geometry group. Blank cells indicate
values Cat were not available from the regression analysis.
In general, He values presented In the table show a
consistency w~thtihe hypotheses and He resuming findings
and conclusions both within and between geometry groups.
However, there are several cell values that are not
consistent and should be re-assessed if a consistent set of
values are to be used as He basis for a final cap acid
model.
Table 67 shows the final set of recommended values,
including the following modifications of several of the
regression results. These modifications, while minor,
provide a consistency between all geometric groups and
degree of conflict cases.
The values for Group 4a sites have been Increased
by 0. ~ seconds to be consistent with the data for
Group 3a sites.
The case ~ headways for Groups 5 and 6 have
been increased by 0.2 seconds Stoat 4.3 to 4.5
seconds) to be consistent wig the Group 4b
values (also 4.5 seconds).
The Group 5, Case 4-2 headway was increased
from7.1 seconds to 7.6 seconds to tee consistent
; with He Group 4b Case 4 value.
The Group 5 Case 5-3 and 5-4 headways were
increased EomS.2to 9.7 seconds end fiom 8.9 to
,.
9.7 seconds respectively to be consistent with the
Group 4a value.
The Group 6 left turn adjustment was Increased
from 0.4 to 0.5 seconds to be consistent wig the
Group 5 value.
The Group 6 nghttum adjustment was set at -0.7
seconds to be consistent with the Group 5 value.
The Groups 5 and 6 heavy vehicle adjuslments
were set to I.7 seconds to be consistent with the
values for the other groups.
50
Table 66. Saturation Headway Values from Regression Analysis
4.7
6 2
s.3
S 8
6 4
7.6
8.2
8.9
10.0
ll.S
. ,-
O.S
-0.7
1.6
Notes: Case is the degree of conflict case. Bumped is the number of opposing and conflicting vehicles faced by the subject approach driver. IT and RT are the
adjushnents forewarning vehicles. Harris the adjus~nent for heavy vehicles. - notes eases that are not applicable.
Table 67. Recommended Saturation Headways for AWSC Intersections
3.9
4.7
9.6
4.0
4.8
~ 9
7.1
3.9 (4.0)
5.1
7.4
4.7 (4~8)
5.8 (5.9)
7.0 (7~1)
4.3 (4~5)
5.3
6.4
7.6
5.0
6.2
7.1 (7.6)
7.8
9.0
4.3 (4~5)
6.0
6.8
7.4
8.1
8.7
9.6
12.3
9.7
10.0
9.6 (9.7)
........................
. G -
, ., , , .. ,, ,
0.2
-0.6
1.7
10.2
8.2 (9.7)
8.9 (9~7)
10.0
11 5
10.0
11.1
11.4
13 3
0.2
-0.6
1.7
0.5
-0.7
1.6 (1.7)
0.4 (0~5)
(-o.7)
(1.~
Notes: Case is the degree of conflict case. NumVeh is the numb" of opposing and conflicting vehicles faced by the suyoct approach driver. LT end RT are the
adjushnents for turning vehicles. HVis the adjustment for heavy vehicles. - notes cases that are not applicable. The values fiom regression analysis are shown first
in the cell; adjacent values in the same cell in pareses are the adjusted and recommended values.
