ITE Western District 2012 Annual Meeting
Applications of High-Resolution Traffic Event Data: Managing Oversaturated Arterials
Dr. Xinkai Wu, Assistant Professor
Department of Civil EngineeringCalifornia State Polytechnic University Pomona
ITE Western District 2012 Annual Meeting
High-Resolution Event Data
08:09:15.012, D8 on, 7.902s 08:09:15.481, D8 off, 0.468s 08:09:16.761, G3 off, 29.389s 08:09:16.761, Y3 on, 179.021s 08:09:17.620, D9 on, 2.686s 08:09:18.151, D10 on, 2.593s 08:09:18.307, D9 off, 0.687s 08:09:18.823, D10 off, 0.671s 08:09:20.244, Y3 off, 3.482s 08:09:21.649, D22 on, 80.953s 08:09:22.008, D22 off, 0.359s 08:09:23.242, G1 on, 172.806s
D e te c to r # 8 o n a t 0 8 :0 9 :1 5 .0 1 2 ;V a c a nt tim e is 7 .9 0 2 s
G re e n P ha s e # 3 o ff a t 0 8 :0 9 :1 6 .7 6 1 ;G re e n d u ra tio n tim e is 2 9 .3 8 9 s
D e te c to r # 9 o ff a t 0 8 :0 9 :1 8 .3 0 7 ;O c c u p y tim e is 0 .6 8 7 s
Y e llo w P ha s e # 3 o ff a t 0 8 :0 9 :2 0 .2 4 4 ;Y e llo w d u ra tio n tim e is 3 .4 8 2 s
G re e n P ha s e # 1 o n a t 0 8 :0 9 :2 3 .2 4 2 ;R e d d u ra tio n tim e is 1 7 2 .8 0 6 s
ITE Western District 2012 Annual Meeting
SMART-SIGNAL Terminal Box
DAC
ITE Western District 2012 Annual Meeting
Trunk Highway 55 and Boone Ave (Golden Valley, MN)
Oversaturation
• Gazis (1963): An oversaturated intersection is defined as one in which the demand exceeds the capacity.
• Little research has been conducted on the identification and quantification of oversaturated conditions– Mostly qualitative and incomplete
1 2
1 21 ( )q q L
s s C
Detrimental Effects
• Temporally, characterized by a residual queue at the end of cycle. – Residual vehicles cannot be discharged due to insufficient
green splits– Creating detrimental effects on the following cycle by
occupying a portion of green time.
• Spatially, characterized by a spill-over from a downstream intersection. – Vehicles cannot be discharged even in green phase due to
spill-over – Creating detrimental effects by reducing useable green
time for upstream movements
Oversaturation Severity Index (OSI)
• OSI: the ratio between unusable green time and total available green time in a cycle.
• Further differentiate OSI into T-OSI and S-OSI. – Temporal dimension (T-OSI) • The “unusable” green: because of the residual queue from
the last cycle
– Spatial dimension (S-OSI)• The “unusable” green: because of the downstream
blockage
Measure T-OSI & S-OSI
• T-OSI: – Estimate the length of residual queue at the end
of cycle
• S-OSI: – Identify spillover – Calculate the reduction of green time of upstream
intersections
ITE Western District 2012 Annual Meeting
T-OSI & S-OSI Measure Using High-Resolution Traffic Event Data
Queue Length Estimation• Instead of traditional input-output approach,
we estimate queue length by taking advantage of queue discharge process
• Based on LWR shockwave theory
Queue Length Estimation• Utilize the data collected by advance detector• Identify Critical Points: A, B, C
D is ta nc e
T im e
1v
2v
ngT
nrT
nTmax1n
gT
3v
nTmin
5v
1nrT
4v
A B CLo o pD e te c to r
H
AT BT CT
dL
nLmax
D
nLmin
Break Point Identification from High-Resolution Detector Data
Case 1 - Long Queue
0
10
20
30
40
50
7:26:07 7:26:50 7:27:33 7:28:16 7:29:00
Case 1 - Long Queue
0
2. 5
5
7. 5
10
7:26:07 7:26:50 7:27:33 7:28:16 7:29:00
D etecto r O ccu p a tio n T im e
B rea k P o in t A B rea k P o in t B
T im e G a p B etw een C o n secu tiv e V eh icles
),( mm kq
),( na
na kq
P attern I : C ap acity con d ition
P attern II : F ree flow arr iv al
B reak P oin t C
(Se c )
(Se c )
T im e
T im e
(a)
(b )
ITE Western District 2012 Annual Meeting
Field Tests• Test Site: TH55 (6
intersections)• Independently evaluated
by Alliant Engineering, Inc.– At Rhode Island Ave.– Three morning peaks
(7:00am-9:00am) • Jul. 23rd, 2008• Occ. 29th, 2008• Dec. 10th, 2008
0
250
500
750
1000
6:57:36 7:26:24 7:55:12 8:24:00 8:52:48
0
250
500
750
1000
6:57:36 7:26:24 7:55:12 8:24:00 8:52:48
0
250
500
750
1000
6:57:36 7:26:24 7:55:12 8:24:00 8:52:48
M a x im u m Q u e u e L e n g th C o m p a ris o n - J u l. 2 3 rd , 2 0 0 8
M a x im u m Q u e u e L e n g th C o m p a ris o n - O c c . 2 9 th , 2 0 0 8
M a x im u m Q u e u e L e n g th C o m p a ris o n - D e c . 1 0 th , 2 0 0 8
D is ta nc e (ft)
D is ta nc e (ft)
D is ta nc e (ft)
T im e
T im e
T im e
O bs e r vat i o n
E s t i m at i o n
O bs e r vat i o n
E s t i m at i o n
O bs e r vat i o n
E s t i m at i o n
T H 5 5
A d v a n ced d etecto rs
a )
b ) R h o d e Isla n d A v e.
G len w o o d A v e.
T H 5 5
S to p b a r d etecto rs
W in n etka A v e .B o o n e A v e .
A d d itio n a l d etecto rs
P h a se 6
P h a se 24 0 0 ft
2 6 3 5 ft 8 4 2 ft 1 7 7 7 ft
3 7 5 ft
SOSI: Identify Queue-over-detector (QOD) Caused by Spillover
Q O D ca u sed b yred in terv a l
D istanc e
T im e
A SC
QODST
OCCSt
QODET
4v2v
Q O D ca u sed b ysp illo v er
S to p -b a r d etecto r
A d v a n ce d etecto r
ngT
nrT
1ngT
OCCEt
E
D o wn str e am
U p str e am
ITE Western District 2012 Annual Meeting
S-OSI: Identification of Spillover
• Identify QOD-II.• High-resolution data.
Occupati on Ti me
6800
7000
7200
7400
7600
7800
17: 12: 20 17: 13: 03 17: 13: 47 17: 14: 30 17: 15: 13
D etector O ccu p an cy T im e for W es tb ou n d T H 5 5 at R h od e Is lan d A v e.D i s tanc e ( fe e t )
Ti m e
O c c upanc y Ti m e o f Advanc e D e te c to r
O c c upanc y Ti m e o f Sto p-bar D e te c to r
2v2vQ O D c a u s e d b y re d p h a s e Q O D c a u s e d b y s p illo v e r
S top -b arD etector
A d v an ceD etector
ITE Western District 2012 Annual Meeting
Managing Oversaturation: A Simple Forward-Backward Procedure
ITE Western District 2012 Annual Meeting
A Simple Forward-Backward Procedure
• Based on TOSI and SOSI measurements• Respond and mitigate traffic congestion quickly • Simple and effective• Reactive
ITE Western District 2012 Annual Meeting
Problem Setting• N intersections along an oversaturated path• At control period t, decisions are made according to the
average TOSI and SOSI values at the control period t-1, i.e.,
1,
1,
( 1)
( 1)i
i
TOSI t
SOSI t
2,
2,
( 1)
( 1)i
i
TOSI t
SOSI t
3,
3,
( 1)
( 1)i
i
TOSI t
SOSI t
,
,
( 1)
( 1)N i
N i
TOSI t
SOSI t
I n te r s ec tio n 1 I n ter s ec tio n 2 I n te r s ec tio n 3 I n ter s ec tio n N
, ,( 1), ( 1)n i n iTOSI t SOSI t
ITE Western District 2012 Annual Meeting
Basic Mitigation Strategies• The TOSI and SOSI values can help identify
the causes of arterial traffic congestion• Positive SOSI indicates the spill-back of
downstream queue• Positive TOSI indicates that the available
green time is insufficient for queue discharge• Therefore for a single intersection, three
basic strategies can be applied.
ITE Western District 2012 Annual Meeting
TOSI > 0
D is ta n ce
Tim e
# n
# n + 1
D is ta n ce
Tim e
S h o c k w a ve Tr a j e c t o r y
.n ig
S h o c k w a ve Tr a j e c t o r y D is ta n ce
1,n ir 1,n ig
,n ir ,n ig,n iO
1,n iO 1,n ir 1,n ig
,n ir ,n ig,n iO
1,n iO
V e h i c l e Tr a j e c t o r y
fv fv
V e h i c l e Tr a j e c t o r y
• Extending green
ITE Western District 2012 Annual Meeting
SOSI > 0
• Reducing red at the downstream intersection
D is ta n ce
Tim e
S h o c k w a ve Tr a j e c t o r y
# n
D is ta n ce
Tim e
1nr 1ng
nr ng
S h o c k w a ve Tr a j e c t o r y
nO
1nO
# n + 1 1ng 1nr 1ng
nr ngnO
1nO
ITE Western District 2012 Annual Meeting
SOSI > 0
• Gating (Reducing traffic arrivals & giving green to other approaches)
D is ta n ce
Tim e
S h o c k w a ve Tr a j e c t o r y
# n
# n + 1
1nr 1ng
nr ngnO
1nO
D is ta n ce
Tim e
S h o c k w a ve Tr a j e c t o r y
1nr 1ng
nr ngnO
1nO
ng
ITE Western District 2012 Annual Meeting
Handling Spillover
D is ta n ce
Tim e
S h o c k w a ve Tr a j e c t o r y
#n
D is ta n ce
Tim e
1,n ig
S h o c k w a ve Tr a j e c t o r y
#n+11, ( )n ir t
V e h i c l e Tr a j e c t o r y
fv
V e h i c l e Tr a j e c t o r y
fv
a) S p illo v e r at in te rs e c tio n n b ) A fte r R e d E x te n s io n & D o w n s tre am R e d R e d u c tio n
, ( )n ir t, ( 1)n iS t
, 1, ,( ) ( ) ( 1), [1, 1]n i n i n ir t r t S t n N
ITE Western District 2012 Annual Meeting
Forward-Backward Procedure
• Forward Process (Seeking the available green)– Follow the flow direction to eliminate spillovers
and residual queues
– Boundary condition
, 1, 1,
, 1, , ,
( ) ( ) ( 1), 2,...,
( ) ( ) ( 1) ( 1)
F Fn i n i n i
F Fn i n i n i n i
r t r t S tn N
g t g t T t S t
1,
1, 1,
( ) 0
( ) ( )
Fi
F ai i
r t
g t g t
ITE Western District 2012 Annual Meeting
Forward-Backward Procedure
• Backward Process (Gating or metering)– Follow the opposing flow direction to check the
arc capacity
– Boundary condition
, 1, , , 1, ,( ) ( ) min ( ) ( ) ( ) ( ) ,0 , 1,...,1B B a F B Fn i n i n i n i n i n ig t g t g t g t g t r t n N
, , , ,( ) min ( ) ( ) ( ) ,0B a F FN i N i N i N ig t g t g t r t
Simulation Test• 22 intersections, Pasadena, CA• Offline control
ITE Western District 2012 Annual Meeting
Simulation Test• TOSI/SOSI Changes
TOSI*Green Time
SOSI*Green Time SOSI*Green Time
TOSI*Green Time
Fair Oaks Ave SB Colorado Blvd. WB
ITE Western District 2012 Annual Meeting
Future Work• The Fundamental Diagram: Congestion
• Safety
• Environment
• Control