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IDENTIFYING INFORMATION
AVERAGE RUNNING SPEED, MAJOR STREET.. 35
PEAK
HOUR FACTOR .....................
1
AREA
POPULATION ......................
100000
NAME
OF THE EAST/WEST STREET.........
drake
NAME
OF THE NORTH/SOUTH STREET.......
west access
NAME
OF THE ANALYST ..................
mJd
DATE
OF THE ANALYSIS (mm/dd/yy)......
6/11/93
TIME PERIOD ANALYZED ................. am omishort
OTHER INFORMATION....
INTERSECTION TYPE AND CONTROL
-- -----------------------------------------------------------------
INTERSECTION TYPE: T-INTERSECTION
MAJOR STREET DIRECTION: EAST/WEST
CONTROL TYPE NORTHBOUND: STOP SIGN
TRAFFIC VOLUMES
EB WP• NB SP.
---- ---- ---- ----
LEFT 0 50 5 --
THRU 513 862 0 --
RIGHT 10 0 30 --
NUMBER OF LANES
---------------------------------------------------------------------
EE; WE. NE'. SE,
------ ------- ------- -------
LANES I i i --
CAPACITY AND LEVEL -OF -SERVICE Pape-3
---------------------------------------------------------------------
POTEN- ACTUAL
FLOW- TIAL MOVEMENT SHARED RESERVE
RATE CAPACITY CAPACITY CAPACITY CAPACITY
MOVEMENT v(pcph) c (pcph) c (pcph) c (pcph) c = c - v LOS
p M SH R SH
------------------------------------------------ ---
MINOR STREET l C ii
NB LEFT 6 108 103 > 103 > 98 > E
> 351 > 312 >6
RIGHT 33 584 584 > 584 > 551 > A
MAJOR STREET
WB LEFT 55 677 677 677 622 A
IDENTIFYING INFORMATION
---------------------------------------------------------------------
NAME OF THE EAST/WEST STREET...... drake
NAME OF THE NORTH/SOUTH STREET.... west access
DATE AND TIME OF THE ANALYSIS..... 6/11/93 am "•short
OTHER INFORMATION....
1985 HCM: UNSIGNALIZED INTERSECTIONS Paae-1
XXXXXXXiXXXXXXXX>XXXXXXYXXXXXXXX XICYXXXXXXXXXXXXXXXXXXYXXXXXXXXXXXXXXX
IDENTIFYING INFORMATION
--------------------------------------------------------------------
AVERAGE RUNNING SPEED, MAJOR STREET.. 35
PEAK HOUR FACTOR ..................... 1
AREA POPULATION ...................... 100000
NAME OF THE EAST/WEST STREET......... drake
NAME OF THE NORTH/SOUTH STREET....... west access
NAME OF THE ANALYST .................. mJd
DATE OF THE ANALYSIS (mm/dd/yy)...... 6/11/93
TIME PERIOD ANALYZED ................. a�mlpm short
OTHER INFORMATION....
INTERSECTION TYPE AND CONTROL
--------------------------------------------------- -----------------
INTERSECTION TYPE: T-INTERSECTION
MAJOR STREET DIRECTION: EAST/WEST
CONTROL TYPE NORTHBOUND: STOP SIGN
TRAFFIC VOLUME
---------------------------------------------------------------------
EB WB NB SB
---- ---- ---- ----
LEFT 0 20 10 --
THRU 769 279 0 --
RIGHT 5 0 40 --
NUMBER OF LANES
---------------------------------------------------------------------
EB WE. NE; Sb
------- ------- ------- -------
LANES 1 I 1 --
CAPACITY AND LEVEL -OF -SERVICE Page-3
---------------------------------------------------------------------
POTEN- ACTUAL
FLOW- TIAL MOVEMENT SHARED RESERVE
RATE CAPACITY CAPACITY CAPACITY CAPACITY
MOVEMENT v(pcph) c (pcph) c (pcph) c (pcph) c = c - v LOS
p M SH R SH
------- ------- --------- ------------ ------------ ---
MINOR STREET
NB LEFT 11 187 182 > 182 > 171 > 0
> 332 > 217 >C
RIGHT 44 419 419 > 419 > 375 > B
MAJOR STREET
WB LEFT 22 502 502 502 480 A
IDENTIFYING INFORMATION
NAME OF THE EAST/WEST STREET...... drake
NAME OF THE NORTH/SOUTH STREET.... west acces
DATE AND TIME OF THE ANALYSIS..... 6/11/93 am ipm short
OTHER INFORMATION....
1985 HCM: UNSIGNALIZED INTERSECTIONS Page-1
..... *.......... *......... .*........ *....... Zt......................
IDENTIFYING INFORMATION
---------------------------------------------------------------------
AVERAGE RUNNING SPEED. MAJOR STREET.. 35
PEAK HOUR FACTOR ..................... 1
AREA POPULATION ...................... 100000
NAME OF THE EAST/WEST STREET......... drake
NAME OF THE NORTH/SOUTH STREET....... hampshire
NAME OF THE ANALYST .................. mid
DATE OF THE ANALYSIS (mm/dd/yv)...... 6/11/93
TIME PERIOD ANALYZED ................. am mmishort
OTHER INFORMATION....
INTERSECTION TYPE AND CONTROL
INTERSECTION TYPE: 4-LEG
MAJOR STREET DIRECTION: EAST/WEST
CONTROL TYPE NORTHBOUND: STOP SIGN
CONTROL TYPE SOUTHBOUND: STOP SIGN
TRAFFIC VOLUMES
---------------
EB WE, NE� SE'
---- ---- ---- ----
LEFT 20 23 4 53
THRU 516 861 i 1
RIGHT 7 111 1_, 47
NUMBER OF LANES AND LANE USAGE
-----------------------------------------------------------------
EF WH NR E.
------- -------------- -------
LANES
CAPACITY AND LEVEL -OF -SERVICE Page-3
---------------------------------------------------------------------
POTEN- ACTUAL
FLOW- TIAL MOVEMENT SHARED RESERVE
RATE CAPACITY CAPACITY CAPACITY CAPACITY
MOVEMENT V(pcph) c (pcph) c (pcph) c (pcph) c = c - v LOS
p M SH R SH
------------------------------------------------ ---
MINOR STREET I& �& CID
NB LEFT 4 86 72 > 78 72 > 72 68 >E E
THROUGH 1 114 108 > 108 > 107 > D
RIGHT 14 583 583 583 568 A
MINOR STREET ZZ-'>'�-
SB LEFT 58 99 91 > 92 91 > 32 33 >E E
THROUGH 1 123 116 > 116 115 > D
RIGHT 52 346 346 346 294 C
MAJOR STREET
EB LEFT 22 396 396 396 374 B
WB LEFT 25 677 677 677 652 A
IDENTIFYING INFORMATION
NAME OF THE EAST/WEST STREET...... drake
NAME OF THE NORTH/SOUTH STREET.... hampshire
DATE AND TIME OF THE ANALYSIS..... 6/11/93 : am Pmishort
OTHER INFORMATION.... —
1985 HCM: UNSIGNALIZED INTERSECTIONS Paae-1
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX<ZXXX.XXXXXXX X XXXXXXSXXX Y.X XXY
IDENTIFYING INFORMATION
---------------------------------------------------------------------
AVERAGE RUNNING SPEED. MAJOR STREET.. 35
PEAK
HOUR FACTOR .....................
1
AREA
POPULATION ......................
100000
NAME
OF THE EAST/WEST STREET.........
drake
NAME
OF THE NORTH/SOUTH STREET.......
hampshire
NAME
OF THE ANALYST ..................
m.jd
DATE
OF THE ANALYSIS (mm/dd/yy)......
6/11/9S
TIME PERIOD ANALYZED. ................ am Pm short
OTHER INFORMATION....
INTERSECTION TYPE AND CONTROL
-------------------------------------
INTERSECTION TYPE: 4-LEG
MAJOR STREET DIRECTION: EAST/WEST
CONTROL TYPE NORTHBOUND: STOP SIGN
CONTROL TYPE SOUTHBOUND: STOP SIGN
TRAFFIC VOLUMES
---------------------------------------------------------------------
ES WB NB SB
---- ---- ---- ----
LEFT 32 7 6 92
THRU 775 281 1 1
RIGHT 2 46 19 12
NUMBER OF LANES AND (LANE USAGE
_____________________________________________________________________
ES WE; NB SEl
-------------- ------- -------
LANES
L. ANE USAGE Ll + P Ll + k
CAPACITY AND LEVEL -OF -SERVICE Page-3
_____________________________________________________________________
POTEN- ACTUAL
FLOW- TIAL MOVEMENT SHARED RESERVE
RATE CAPACITY CAPACITY CAPACITY CAPACITY
MOVEMENT v(pcph) c (pcph) c (pcph) c (pcph) c = c - v LOS
0 M SH R SH
_______ _________________ ____________ ____________ __
MINOk STREET 7AIPIC
NB LEFT 7 164 156 > 160 156 > 153 149 >D D
THROUGH 1 201 194 > 194 > 193 > D
RIGHT 21 416 416 416 395 B
MINOR STREET I K- '-'K D
SB LEFT 101 168 157 > 157 157 > 55 56 >E E
THROUGH 1 208 201 > 201 > 200 > C
RIGHT 13 754 754 754 740 A
MAJOR STREET
EB LEFT 35 843 843 843 808 A
WB LEFT 8 500 500 500 492 A
IDENTIFYING INFORMATION
NAME OF THE EAST/WEST STREET...... drake
NAME OF THE NORTH/SOUTH STREET... hampshire
DATE AND TIME OF THE ANALYSIS..... 6/11/93 amjpm short
OTHER INFORMATION....
APPENDIX D
Tile conflicting flow of the minor left turn — 1227
vph. Using Figure 10-3 in the HCH, a critical gap of
approximately 4.5 seconds is located for a potential
capacity of 378 and a conflicting flow of 1227. These
steps are illustrated in the flow chart in Figure 4.
Under the future conditions, the conflicting flow is
estimated to increase to t400 vph, and the minor left
turn demand will increase to 170 vph. The future
potential capacity located on Figure 10-3 is 300 vph
for a gap of 4.5 seconds and conflicting flow of 1400
vph.
The actual capacity accounts for the impedance factor
(for this example the impedance factor is assumed to
be 0.98).
Cm7 — 300 x 0.98 — 294 vph
The reserve capacity — 294 - 170 — 124 vph,
and the average delay Is calculated using equation (2),
Delay — 3600 — 29.0 sec.
124
The level of service for the future conditions will be
LOS D.
CONCLUSION
The methodology presented in this paper provides one
way to quantify the operation of an unsignalized inter-
section when the HCH methodology does not correlate
with field observations. Future operating conditions
can also be defined on the basis of existing
conditions delay data. The delay methodology should
not be used for intersections with high accident
experience or where vehicles on the side street are
forcing a gap in the major street traffic stream.
Further research is needed for intersections with a
shared lane on the minor approach since the right turn
delay is affected by the left turn movement. Data
collected for the left turn movement on a shared lane
approach should not be significantly affected.
Delay is a measure of effectiveness that should be
applied to unsignalized intersections because it is
easily ^=asured and also easily understood. Future
revisions of the HCH methodology should include
delay.
REFERENCES
1. Transportation Research Board, National Research
Council. "Research Problem Statements: Highway
Capacity", Transporation Research Circular Number
319. Washington D.C., June 1987, page 27.
2. Institute of Transporation Engineers.
Tran voration and Traffic EneineeriUg Handbook.
Prentiss Hall Inc.; 1982, pp. 499-536.
3. Roess, Roger P. and McShane, William R. "Changing
Concepts of Level of Service in the 1985 Highway
Capacity Manual: Some Examples," ITS Journal, Hay
1987, pp. 27-31.
FIGURE 4
ESTIMATING FUTURE LOS FLOW CHART
Existing Future
Conditions Conditions
Measure Future LOS
Delays I I
Table 1
Avg, Delay I I Avg. Delay
Fer vehicle Per vehicle
Equation (3) Equation (2)
Capacity of Reserve Cap.
Movement Subtract
Equation (4) Demand
Impedance Actual
Factor Capacity
Equation (5) I Equation (6)
Potential Potential
Capacity Capacity from
Equation (6) HCIi Fig. 10-3
Critical Cap Assume Same
11CH Fig. Critical Gap
10-3 for Future
4. Beass, Karsten G. "The Potential Capacity of
Unsignalized Intersections", ITF.Journal, October,
1987, pp. 43-46.
5. Transportation Research Board, National Research
Council. Ni¢hwav Capacity Manual
, Special Report
209. Washington D.C., 1985.
—4—
Intersections with a shared lane on the minor approach
provided conflicting results for the left and right
turn movements. In many cases, the critical gap
determined from the delay data for the right turn was
higher than the gap determined for the minor left
turn. This phenomenon is most likely due to the time
a right turner spends waiting in queue behind a left
turner. Because of the queue, the measured delays for
the two movements were not dramatically different.
Since the critical gap calculation relies on the
movement's conflicting flow, the right turn gap
calculates to a higher value then the left turn gap.
Generally, the minor left turn is the most critical
movement at an Intersection, and the delay data for
the left turn is not significantly affected by a
shared lane. In retrospect, if delay data
measurements did not include stopped delays in a
queue, then the calculated gaps would be higher for
left turns than right turns in all instances.
However, not recording delays in a queue would give an
unfair representation of existing field conditions.
To further illustrate the shared lane phenomenon
affecting right -turning vehicles, the results in
Figures 1 and 2 show a large disparity between the
calculated delays vs. measured delays. However, in
the case of right -turning vehicles, the measured
delays were only 2-3 seconds less than the calculated
delays. The presence of left -turning vehicles in the
shared lane had, most likely, a significant impact on
the delay values recorded for right -turning vehicles.
Further research on shared -lane approaches is needed.
ESTIMATING FUTURE LEVEL OF SERVICE
The following procedure is suggested to estimate
future level of service from existing delay data. It
relies on the existing ITCH methodology, and basically
back -calculates from delay to capacity to determine
the gap being accepted by drivers. Once the gap is
determined, the future capacity and level of service
can be estimated using the same gap.
The capacity for an unsignalized intersection movement
can be determined from delay by rearranging equation
(2) as follows:
capacity (veh/hr) " 3600 (sec/hr_ , Side Street Demand (4)
Average Delay (see/veh)
The ITCH equations relate critical gap to "potential
capacity." The potential capacity for the left turn
from the major street and right turn from the minor
street are the same as capacity, but the capacity of
the minor left turn needs to be converted to potential
capacity discounting the impedance factor of the major
left turn. The impedance factor is determined using
the following equation (the variable names
correspond to the variables in IICM):
V 1.2052
0.0038 �100 x C4
p4
I — Impedance Factor
V4 — Left turn volume from major street
Cp4 — Capacity of left turn from major street
The potential capacity of the minor left turn is then
calculated using:
_ Cm7 (6)
Cp7 I
C 7 — Potential capacity of the minor left turn
Cm7 — Actual capacity of the minor left turn
(determined from delay data)
Using Figure 10-3 in the 1985 ITCH, the critical gap
can be estimated from the potential capacity and
conflicting flow. Alternatively, the equations In
Karsten G. Baoss' article "The Potential Capacity of
Unsignalized Intersections" (ITE Journal, October
1987, pp. 43.46.) can be used to determine the gap.
The estimated critical gap may be lower than 4.0
seconds for low volume locations, but it is
recommended that 4.0 be the minimum gap used. HCH's
Figure 10-3 also `shows the minimum critical gap to be
4.0 seconds.
Once the critical gap is estimated from the delay
data, the future level of service at a location is
determined using the standard ITCH methodology. This
methodology is not recommended for intersections with
high accident experience, or where vehicles on the
side street are forcing a gap in the major street
traffic stream. The following is an example of this
methodology's application:
EXAMPLE:
A delay study and turning movement count were
performed at the T-intersection of Lincoln Avenue and
Bristow Street in Saugus, Massachusetts. The PM peak
hour turning movement volumes and vehicle delays are
summarized below:
Average
Peak Mour conflicting Delay per Maximum Semple
Movement Volume Flou Vehicle Delay Size
Minor left 101 1227 13.7 64 92
Minor Right 33 653 5.4 28 31
Major left 36 653 3.8 14 Is
According to the IICM methodology, the left turn from
Bristow Street to Lincoln Avenue operates at LOS F.
The delay study data, however, show that the left turn
operates at LOS C.
The capacity of each movement is calculated using
equation (4).
Movement Demand Capacity
Minor Left 107 vph 370 vph
Minor Right 33 760
Major Left 36 983
The potential capacity of the minor left turn is
(5)
calculated using the impedance factor from equation
(5). The impedance factor is determined from the
demand and capacity of the major left turn,
0.0038(100 x_¢)1.2052 _ 0.98
983
and potential capacity,
CP7 — 370 — 378 vph
0.98
—3—
MEASURED DELAY VS. CALG9IIATED DELAY
Delay studies at unsignalized intersections are
relatively easy to perform and can be performed in
conjunction with a turning movement count at low
volume Intersections. The observer measures the time
between when a vehicle stops for a stop sign or
conflicting traffic and pulls onto the major street.
The measurement includes the time waiting In queue.
The stopped delay is measured for random vehicles
turning left or right from the minor street or turning
left from the major street. The average delay during
the peak hour is calculated using a modified
signalized intersection delay equation:
Average Delay (sec/Yeh) • Total Delay (sec) (3)
Number of observations
For locations with a shared lane for left and right
turns on the minor street, the stopped delay for each
movement should be kept separate if future conditions
will be projected from the data since the level of
service of each movement is calculated separately and
then combined as a shared lane movement. Special
consideration, discussed later, should be given to
shared lane approaches where the right turn delay will
be increased by a high left turn volume. The existing
level of service for the shared lane is the weighted
average of the combined movements.
Bruce Campbell b Associates performed delay studies at
more than 50 unsignalized Intersections in eastern and
central Massachusetts. For all study locations, a
traffic count was also performed, and the level of
service was calculated using the ITCH methodology. To
date, only a few delay studies have been performed at
4-legged intersections, so only the data for
T-intersections are included in this paper. The
average delay per vehicle was calculated using
equation (3). Figures 1 through 3 compare the results
of the measured delay and the calculated delay. The
curves are from regression equations relating
conflicting flow and average delay. At this point
there have been no attempts to correlate the delay
data to another variable such as speed, movement
demand or type of control.
For all three critical movements at an unsignalized
intersection --tile left turn from the minor street,
right turn from the minor street and left turn from
the major street --the measured delay was found to be
shorter than the calculated delay. These data suggest
that drivers are selecting smaller gaps than those
recommended in the 1985 BCH. Using tile methodology
described below to back -calculate to the critical gap,
it was found that at over 80 percent of the locations,
the critical gap for both the minor left and right
turn movements was less than 6.0 seconds.
It was originally suspected that the smaller gap size
determined for the study locations would result in
higher accidents rates at these locations. however,
most of the intersections studied had accident rates
less than 0.5 Ace/Million Entering Vehicles, and none
had accident rates over 2.0 Acc/HEV, In
Massachusetts. Intersections with an accident rate of
less than 2.0 are not considered high accident
locations.
u
n
n
to
FIGURE 1
CONFLIC1111G FLOW VS. AVERAGE DELAY
lThomende)
COTSUCTNG FLOW
FIGURE 2
CONFLICTING F(LLOIR_VSr AYES RErEI D AY
e 0.2 0.4 CIA 02 1 1.2 ,., ,.a ,,a ,
(Thousandal
cONRICIM FLOW
FIGURE 3
CONFLICTING FLOW VS. AVERAGE DELAY
RI(i II IU(N FROM MNOR STREET
0.:
(Thowe,d91
COhFIICTNG FLOW
ULCULAI EO
ME��EO
-2!
A HEIlI0D0IJD(:Y FOR USING DELAY STUDY DATA
TO ESTIRATE TmE ERISIING AND FUTURE LEVEL OF SERVICE
AT UNSICNALIZED INTERSECTIONS
By Marni fleffron (A)o and Georgy Bezkorovainy (H)b
INTRODUCTION
The level of service at unsignalized intersections is
often overstated by the 1985 i(lghway Capaclty
Hanual (ITCH) methodology. The ITCH analysts for
unsignalized Intersections may show a LOS E or LOS F
operation with lengthy delays and, presumably, long
queues. flowever, from field observation, the
intersection functions relatively well with Short
queues and minor delays on the approaches controlled
by STOP signs and no delays to mainline traffic. Many
reviewing agencies require the use of the NCH
methodology to determine level of service. However.
11CM'states that "because the methodologies (for
calculating unsignalized level of service) result in a
qualitative evaluation of delay, it is also
recommended, if possible, that some delay data be
collected. This will allow for a better
quantification and description of existing operating
conditions at the location under study." HCH does
not, however, include a methodology to relate delay
study results for an unsignalized intersection with a
level of service designation.
11CM defines the level of service of an unsignalized
Intersection using "reserve capacity", an
analytically -defined variable that is not easily
field -verified. The procedure Is based on the German
method of capacity determination at rural
intersections. This method ties not been extensively
validated or calibrated for U.S. conditions, nor does
it estimate delay in quantitative terms.
This paper presents a methodology to use delay study
data to determine the existing level of service and to
estimate future operating conditions at unsignalized
intersections. in developing the methodology, delay
studies :ere performed at more than 50 unsienalized
T-intersections in eastern and central Hassechusetts.
minor approaches of these intersections were
controlled by stop signs, yield signs and uncontrolled
(implied yield). The results of these delay studies
will also be compared to the delay calculated using
the ITCH unsignalized intersection analysis.
This paper relies on the existing HCH methodology as
the basis to estimate existing and future level of
service from delay data. Until changes are made in
tile 11CH procedure, the existing NCH methodology for
unsignalized intersections will continue to be
modified to yield results that better approximate
existing and future conditions.
a Transportation Engineer
Bruce Campbell 6 Associates, Boston MA
b vice President
Bruce Campbell 6 Associates, Boston i(A
UNSICNALIZED INTERSECTION DELAY
Delay was adopted as a measure of effectiveness for
signalized intersections in the 1985 ITCH for many
reasons: two reasons are that the concept of delay is
understood by the user community and delay can be
measured In the field.3 The application of delay
for unsignalized intersections should follow this same
reasoning. The.,,reserve capacity is related to
average vehicle delay using the following equation
from the TIE llandbook2:
(1)
d (a - b)
d — average delay
a — service rate
b — side -street arrival rate
Recognizing that capacity is the service rate and
volume is the arrival rate at an unsignalized
Intersection, this formula shows that the average
vehicle delay is the reciprocal of reserve capacity.
The average seconds of delay per vehicle is calculated
using the following equation:
Averege Delay (sec/veh) " 3600 (sec/hr) (27
Reserve Capacity (veh/hr)
Table 1 shows the level of service designations which
correspond to reserve capacity and average vehicle
delay. Because the average delay per vehicle
approaches infinity as the reserve capacity goes to
zero, LOS F will be defined by any delay over 60
seconds. The average delay values for unsignalized
Intersections shown in Table 1 are very similar to the
delay values used to define the level of service of
signalized intersections. Table 1 is taken from Table
10-3 in the 11CH.
Iable 1
Level -of -Service Criteria
For Unsignalized Intersections
Average **
Level of Reserve Capacity Stopped Delay
Service (Pass Cars Per Hour) (sec/veh)
p > 400 < 9.0
g 300 - 399 9.1 to 12.0
C 200 - 299 12.1 to 18.0
-D 100 - 199 18.1 to 36.0
E 0 - 99 36.1 to 60.0
F e > 60.0
* Demand exceeds capacity: extreme delays will be
encountered
** Calculated from Equation (2)
—1—
RESERVE CAPACITY (peph)
COMPARISON OF RESERVE CAPACITY AND DELAY
FOR RIGHT TURNS AT A T-INTERSECTION
149
District 6 1990 Annual Meeting
Intersection Delay At Unsignalized Intersections
RESERVE CAPACITY (Peph)
COMPARISON OF RESERVE CAPACITY AND DELAY
Figure I FOR LEFT TURNS AT A T-INTERSECTION
Figure 2
Figure I shows the plot of calculated reserve
apacity versus calculated delay per approach
vehicle for the right turns. The results of the
graphical analysis are also plotted. By calculat-
ing confidence interval as a range of delay per
approach for each calculated reserve capacity,
a reasonable prediction of delay can be made.
For example, a calculated reserve capacity of
400 peph would yield a delay per right-tum
approach vehicle of 10-15
seconds.
Figure 2 shows the plot of calculated reserve
apacity versus calculated delay per approach
vehicle for left turns. The results of the
graphical analysis are also plotted Using the
:onfrdence interval, a prediction of the range
A delay can be made. However, the data for
:he left turns is all in the -100 to +200 range
A values. Therefore, the delay for left turns
s only valid for reserve capacities at the lower
and of the scale using the data considered in
:his atudy. For example, a calculated reserve
:apacity of 100 pcph would yield a delay per
eft -turn approach vehicle of 12-22 seconds.
the size of this range indicates that more data
s needed to reduce the prediction range.
ZZONCLUSIONS
liven the limited data obtained (61 observa-
ions), it appears as though the methodology
:an give a reasonable indication of the range
if delay for vehicles entering a street at a stop
:ign controlled T-intersection. However, more
lata is needed to fill in gaps:
Data is needed at intersections where
the right turns operate at levels of
service B, C, D, E
Data is needed at intersections where
the left turns operate at levels of ser-
vice A, B, C-
1t a number of the analyzed intersections,
here were signals upstream from the analyzed
atersections. Some of these signals were as
147
close as 1/4 mile away. There was no signal
progression pattern on the major street.
However, it was noticed that both operation
and delay were influenced by vehicle queues
created by the signals on the main street. This
was not accounted for in any of the calcula-
tions or analyses. An effort should be made to
select intersections which are not affected by
main street signals.
The statistical analysis on this data and addi-
tional data should be much more rigorous than
that used in this analysis. The curves devel-
oped using all the data should be mathemati-
cally derived and adequately tested using
accepted statistical practices.
The data presented is only for a T-intersection
with a four -lane (plus left -turn lane) main
street with a posted speed of 35 mph. Data
should also be collected at a number of main
street posted speeds (45 mph and 55 mph).
Data should also be collected for a T-intersec-
tion on a two-lane street at various posted
speed limits.
If the additional data and analyses for a T-
intersection point toward the validity of this
approach, then similar data should
be collected and analyses performed at four -
leg intersections.
BIBLIOGRAPHY
Box, Paul D. and Joseph C. Oppenlander;
PhD. Manual of Traffic Engineerine Studies,
4th Edition. Arlington, Virginia: Institute of
Transportation Engineers, 1976, Pgs. 106-112.
Roess, Roger P. et al. Highway Capacity
Manual • Special Report 209. Washington,
D.C-: Transportation Research Board, 1985,
Chapter 10.
REFERENCE
1. "Merkblatt for Lichtsignalanlagen an Land-
strassenAusgabe 1972", Forschungsgeselischaft
Intersection Delay At Unsignailzed Intersections
fur das Strassenwesen, Koln, Germany (1972).
Intersection Delay At Unsignalized Intersections
Matthew J. Delich, P.E.
Private Consultant
Loveland, Colorado
BSTRACT
he technique described in the Hi hw
capacity Manual. Special Report 209, Chapter
0, Unsignalized Intersections relates a calcu-
tied reserve capacity to level of service to a
cry unspecific description of expected delay.
lie signalized intersection technique in the
lighwav Capacity Manual relates level of
:rvice to a range of stopped delay per vehicle.
: would seem to be consistent to relate level
f service at an unsignalized intersection to a
Inge of actual delay per approach vehicle
'his research provides some limited data on
itersection delay related to the calculated
:serve capacity at selected T-intersections. At
ie time traffic volumes were collected, inter-
xtion delays were also obtained for selected
tovements. The intersection delay technique
described in the Manual of Traffic Engineer-
ig Studies. TTE,1976, Chapter 8. By compar-
ig the calculated reserve capacity using the
punted traffic volumes to the observed aver-
ge delay per approach vehicle, a table of
elays per approach vehicle could be deter -
dried. This, in turn, could be plotted to
etermine a range of delay given a calculated
:vel of service.
VTRODUCTION
he means of evaluating the operation at an
asignalized intersection is by determining the
vel of service. The procedure in the 1995
iiebwav Capacity Manual (HCM) is primarily
145
taken from a German document (reference 1),
which uses gaps in the major traffic stream
utilized by vehicles crossing or turning through
that stream.
In the HCM, the level of service is related to
vehicle delay. This is especially true in the
evaluation at a signalized intersection. Howev-
er, in the case of an unsignalized intersection,
level of service is related to a nebulous mea-
sure of delay that can mean different things to
different people.
RESEARCH OBJECTIVES
This research was undertaken to relate level of
service to a definitive range of vehicle delay
for the minor street traffic flow. The objec-
tives of the research were:
1. Compare the level of service (reserve
capacity) to a range of vehicle delay, in
seconds, for the stopped traffic on the
minor street.
2. Determine a curve which best de-
scribes that range of vehicle delay.
RESEARCH APPROACH AND LIMITA-
TIONS
Traffic counts were conducted at a number of
stop sign controlled intersections in Fort
Collins, Colorado and Cheyenne, Wyoming.
These volumes were used to determine reserve
capacity in passenger cars per hour (pcph)
Intersection Delay At Unsignalized Intersections
according to procedures documented in the
HCM. Highway capacity software developed
by the Federal Highway Administration, U.S.-
D.O.T. was used to perform these calculations.
Along with the traffic volumes, vehicle delay
was measured for each approach vehicle
according to procedures described in Chapter
8, 'intersection Delays," Manual of Traffic
Engineering Studies.
Due to changes in critical gap size due to
speed, number of lanes on the major street,
and number of legs at the intersection, only T-
intersections were evaluated. Further, in all
cases, the major street was five lanes (4
through lanes and one left -turn lane) and the
speed limit on the major street was 35 mph.
INTERSECr1ON DELAY STUDY
At the time traffic volumes were obtained at
each of the intersections, traffic delays were
also obtained for both right- and left -turning
vehicles from the minor street. The methodol-
ogy used was a procedure which involved
counting the number of vehicles occupying an
intersection approach (right- or left -turn lanes
constitute two approaches) at successive time
intervals for the observation period. The
successive time interval selected was every 15
seconds. Each successive count represented
an instantaneous density or number of vehicles
occupying the intersection approach per time
interval. These counts were accompanied by
total volume counts of each approach. The
average delay per vehicle in each approach can
be expressed by:
D = Nt/V
where:
D = Average delay per approach vehicle
N = Total density count, or the sum of vehi-
cles observed during the periodic density
counts each t seconds
t = Time intervals between density observa-
tions (15 seconds)
V = Total volume entering the ap-
proach during the study period.
A total of 61 fifteen minute observations were
conducted. The average delay per approach
vehicle for both right and left turns for each
observation was tabulated. The calculated
delays were rounded to the nearest whole
second. The calculated delay per approach
vehicle for right turns ranged from 2 seconds
to 29 seconds. The mean was calculated at 9.9
seconds. The calculated delay per apprr--h
vehicle for left turns ranged from 6 secoi
105 seconds. The mean was calculated at ..,.d
seconds.
LEVEL OF SERVICE CALCULATION
Using the same 15 minute periods from the
intersection delay study portion of this re-
search, level of service calculations were per-
formed. Since the level of service calculation
requires hourly traffic, the volumes for each 15
minute period was factored by four. This not
only gives an hourly volume, but also assumes
a peak hour factor of 1.0.
Reserve capacity in passenger cars per hour
(pcph) was tabulated for the right turns and
left turns for each observation. The calculated
reserve capacities ranged from 36 to 882 pcph
for the right turns. The mean was calculated
at 5655 pcph. Most of the calculated le•• ' of
service were in the A category (> 400 �.
The calculated reserve capacities ranged from -
75 to 241 pcph for the left turns. The mean
was calculated at 66.9 pcph. Most of the
calculated levels of service were in the D
category (100-200 pcph), E category (0-100
pcph), and F category (< 0 pcph).
ANALYSIS
Using the output data for right turns and left
turns from the delay study and the capacity
study, each corresponding observation point
was plotted and least squares graphical analysis
was performed.
INTERMOUNTAIN SEC_TION
BOISE IDAHO JULY i5-18, 1990
Compendium of
Technical Papers
Institute Of Transportation Engineers
43rd Annual Meeting
Boise, Idaho
July 15-10. 1990
APPENDIX C
1985 HCM: UNSIGNALIZED INTERSECTIONS Page-1
......... * 1 .... 1 ......... *... *.... .............. ........ * * *..........
IDENTIFYING INFORMATION
---------------------------------------------------------------------
AVERAGE RUNNING SPEED. MAJOR STREET.. 35
PEAK HOUR FACTOR ..................... 1
AREA POPULATION ...................... 100000
NAME OF THE EAST/WEST STREET......... drake
NAME OF THE NORTH/SOUTH STREET....... hampshire
NAME OF THE ANALYST .................. mJd
DATE OF THE ANALYSIS (mm/dd/yy)...•.. 5/20/93
TIME PERIOD ANALYZED ................. am �m 999 short
OTHER INFORMATION....
INTERSECTION TYPE AND CONTROL
---------------------------------------------------------------------
INTERSECTION TYPE: T-INTERSECTION
MAJOR STREET DIRECTION: EAST/WEST
CONTROL TYPE SOUTHBOUND: STOP SIGN
TRAFFIC VOLUMES
---------------
EB WB NB SB
---- ---- ---- ----
LEFT 19 0 -- 51
THRU 457 763 -- 0
RIGHT 0 108 -- 45
NUMBER OF LANES
---------------------------------------------------------------------
EB WB NB Se.
------- ------- ------- -------
LANES --
CAPACITY AND LEVEL -OF -SERVICE Page-3
POTEN- ACTUAL
FLOW- TIAL MOVEMENT SHARED -RESERVE
RATE CAPACITY CAPACITY CAPACITY CAPACITY
MOVEMENT v(pcph) c (pcph) c (pcph) c (pcph) c = c - v LOS
p M SH R SH
------- -------- --------- ----------- ---
MINOR STREET
SB LEFT 56 134 130 130 74 E
RIGHT 50 393 393 393 343 B
MAJOR STREET
EB LEFT 21 448 448 448 428 A
IDENTIFYING INFORMATION
NAME OF THE EAST/WEST STREET...... drake
NAME OF THE NORTH/SOUTH STREET.... hampshire
DATE AND TIME OF THE ANALYSIS..... 5/20/93 : am m 1993 short
OTHER INFORMATION....
1985 HCM: UNSIGNALIZED INTERSECTIONS Page-1
•t}11ft111tftt4...... *.11tttflltltttllttttl.....ttt 1111ttt t11t1ttt11f•
IDENTIFYING INFORMATION
AVERAGE RUNNING SPEED, MAJOR STREET.. 35
PEAS HOUR FACTOR ..................... 1
AREA POPULATION ...................... 100000
NAME OF THE EAST/WEST STREET......... drake
NAME OF THE NORTH/SOUTH STREET....... hampshlre
NAME OF THE ANALYST .................. mjd
DATE OF THE ANALYSIS (mm/dd/yy)...... 5/20/93
TIME PERIOD ANALYZED ................. O fna short
OTHER INFORMATION....
INTERSECTION TYPE AND CONTROL
------------------------------------------------------
INTERSECTION TYPE: T-INTERSECTION
MAJOR STREET DIRECTION: EAST/WEST
CONTROL TYPE SOUTHBOUND: STOP SIGN
TRAFFIC VOLUMES
EB NB NB SB
---- ---- ---- ----
LEFT 30 0 -- 89
THRU 692 247 -- 0
RIGHT 0 47 -- 11
NUMBER OF LANES
EB WB NB SB
--------------------- -----
LANES 1 1 -- 2
CAPACITY AND LEVEL -OF -SERVICE
Page-3
POTEN- ACTUAL
FLOW- TIAL MOVEMENT SHARED RESERVE
RATE CAPACITY CAPACITY CAPACITY CAPACITY
MOVEMENT v(pcph) c (pcph) c (pcph) c (pcph) c - c - v LOS
p M SH R SH
------------------------------------------------ --- -
MINOR STREET jZ-Z Z
SB LEFT 98 209 204 204 106 D '
RIGHT 12 786 786 786 774 A
MAJOR STREET
EB LEFT 33 876 876 876 843 A
IDENTIFYING INFORMATION
-------------------------------------------------------------
NAME OF THE EAST/WEST STREET...... drake
NAME OF THE NORTH/SOUTH STREET.... hampshire
DATE AND TIME OF THE ANALYSIS..... 5/20/93 short
OTHER INFORMATION.... vv
APPENDIX B
M
MATTHEW J. DELICH, P.E.
3413 BANYAN AVENUE
LOVELAND, CO 80538
TABULAR SUMMARY OF VEHICLE COUNTS
Observer Date 17 9 3 Day �Q N bA 4� city Fo t2 7 `GLL J AJ S R = Right turn
(�AMPS4(PL:: i7 r? �AKC- S= StrLeta r
INTERSECTION OF AND L =Lett turn
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APPENDIX A
J
HAMPSHIRE
195'
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80'
Ti
195'
ROAD
_ _West
�— Access
I
RECOMMENDED LEFT -TURN LANE
GEOMETRY
44Z
Scale:
1" = 50'
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Figure 3
ntersection
Drake/Hampshire
NB
LT/T
NB
RT
SB
LT/T
SB
RT
EB
LT
WB
LT
Drake/West Access
NB
LT
NB
RT
WB
LT
Table 3
Short Range Peak Hour Operation
Level of Service
AM PM
D (A/B/C)* E (C/D)*
B A
E (D)* E (D)*
A C
A B
A A
D (A/B/C)* E (C/D)*
B A
A A
( )* Level of service based upon recent research regarding vehicle
delay.
Intersection
Drake/Hampshire
SB LT
SB RT
EB LT
Table 1
1993 Peak Hour Operation
Level of Service
AM PM
D (C/D)* E (C/D)*
A B
A A
( )* Level of service based upon recent research regarding vehicle
delay.
Land Use
74 Single Family D.U.
Table 2
Trip Generation
Daily A.M.
Peak
P.M.
Peak
Trips Trips
Trips
Trips
Trips
in
out
in
out
710 14
41
48
27
DRAKE
LO�
�CO
30/19 -r
692/457 -+-
w
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'*1-- 47/108
-+- 247 /76
AM / PM
1993 PEAK HOUR TRAFFIC Figure 1
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LO
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7/23
769 513 - f 32 20
5/10 --� 77516
2/7
Hampshire Pond
AM/PM
SHORT RANGE PEAK HOUR TRAFFIC Figure 2
extended at the West Access to the west curb extended at
Hampshire Road. This distance is 330 feet. Based upon Design
Criteria and Standards for Streets, City of Fort Collins, July
1986, pg. 16, the deceleration length should be 310 feet
(interpolated). This is longer than the deceleration distance
(275 feet) shown in A Policy on Geometric Design of Highways
and Streets, AASHTO, 1964, pg. 1044 and in "Intersection
Channelization Design Guide, " NCHRP 279, TRB, 1985, pg. 55.
Considering the above references, the design shown in Figure
3 provides deceleration for both left -turn lanes. The design
shown can be striped in a center median lane on Drake Road.
This design provides 80 feet of full width left -turn lane and
195 feet of taper for a total of 275 feet of deceleration for
both left -turn lanes.
Appendix B. All movements operate acceptably, except for the
southbound left turns during the afternoon peak hour. These
operate at level of service E. Recent research (provided in
Appendix C) indicates that the 1965 HCM technique overstates
the level of service. Table 1 also shows the level of service
applying this recent research. This research indicates that
the operation is acceptable. Acceptable operation is defined
as level of service D or better.
Hampshire Pond is a residential development, consisting
of 74 single family detached dwelling units. Table 2 shows
the expected daily and peak hour trip generation using rates
contained in Trip Generation, 5th Edition, ITE. The trip
distribution used was 75% to/from the east and 25% to/from the
west.
Figure 2 shows the short range traffic assignment at the
key access intersections for Hampshire Pond. This assignment
also includes a modest increase in background traffic on Drake
Road. The recently approved "Fox Creek" development is
reflected in the background traffic. Since the West Access
will also provide access (albeit somewhat circuitous) to the
north/south collector in this area, the turning movements were
increased to reflect this connection. The key intersections
operate as indicated in Table 3. Calculation forms are
provided in Appendix D. Operation will be acceptable at the
key intersections when considering the cited research. Delays
for northbound and southbound left turns at the
Drake/Hampshire intersection may range from 15-30 seconds,
depending upon the time of day.
The eastbound left turns at the Drake/Hampshire
intersection are at levels of service A and B during the
respective morning and afternoon peak hours. This indicates
that the delay will be from 0-12 seconds per approach vehicle.
Using the afternoon peak hour as the worst case and a
conservative peak hour factor of 0.20 (actual is 0.59), two
left -turning vehicles will arrive spaced at 36 seconds. With
an expected maximum delay of 12 seconds, there will not likely
be more than one vehicle waiting to make an eastbound left
turn. The westbound left turn at the West Access will operate
at levels of service A and B. The expected delay will be 0-
12 seconds per approach vehicle. Using the conservative 0.20
peak hour factor, two vehicles will arrive spaced at 14
seconds. This also indicates that there will not likely be
more than one vehicle waiting to make a westbound left turn.
It is concluded that in the left -turn lanes on Drake Road, it
is not necessary to consider storage length.
Given the above conclusion, then only deceleration need
be considered in striping the left -turn lanes on Drake Road
between Hampshire Road and the West Access to Hampshire Pond.
While the centerline to centerline distance is 370 feet, the
design of the left -turn striping should be from the east curb
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Date:
MEMORANDUM
Richard Storck, Storck Development
Rick Ensdorff, Fort Collins Transportation Division
Matt Delich
June 14, 1993
Subject: Hampshire Pond left turn analysis
(File: 9334MEM2)
Hampshire Pond is a single family detached residential
development, located south of Drake Road and west of Taft Hill
Road in Fort Collins. Specifically, it is across from the
Drake/Hampshire intersection. Access will be provided by
extending Hampshire Road south of Drake Road. A second access
is proposed 370 feet (on centers) west of Hampshire Road.
This access provides a second point of access to this parcel
which is not adjacent to any other public street. Concern was
expressed that the two intersections were too close and left -
turn conflicts would result.
Drake Road is designated as an arterial street. In this
area, it currently has a two lane cross section. There is
curb and gutter on the north side of Drake Road. When Drake
Road is widened to the full arterial cross section, all
widening will occur on the south side. The posted speed limit
on Drake Road is 35 mph.
Hampshire Road functions as a collector street north of
Drake Road. It has a continuous, curvilinear alignment from
Drake Road to Prospect Road, which is the next arterial street
to the north. Hampshire Road has stop sign control at its
intersection with Drake Road. Drake Crossing Shopping Center
is adjacent to Hampshire Road. Primary access to Drake
Crossing Shopping Center occurs directly from Drake Road, east
of Hampshire Road and Taft Hill Road. A windshield survey of
Hampshire Road indicates that development along it is
virtually complete.
Peak hour traffic volumes were obtained at the Drake/
Hampshire intersection in May, 1993. These counts are
presented in Figure 1. Raw data is provided in Appendix A.
During traffic counting, the eastbound left turns on Drake
Road were particularly observed. There was virtually no wait
to execute these left turns. While the through traffic and
left turns are in a shared lane, the left -turning traffic did
not delay the through traffic. This intersection was
evaluated using the 1985 Highway Capacity Manual (1985 HCM)
technique for unsignalized intersections. Table 1 shows the
result of this analysis. Calculation forms are provided in