Examination of a Quality Control
Forecast Model for Transit New
Starts Projects
Arash Mirzaei P.E.
Huimin Zhao Ph.D., P.E.
North Central Texas Council of Governments
11th TRB National Transportation Planning
Application Conference
May 9th, 2007
Acknowledgement
• Ken Cervenka, NCTCOG
• Jim Ryan, FTA
• Nazrul Islam, FTA
• DCTA Project Team
2
Disclaimer
• Work in Progress
• Preliminary Results and Conclusions
3
Outline
• Objectives
• Mode Choice Model at NCTCOG
• SUMMIT for New Starts
• Incremental Logit Model
• Transit Skim
• Comparison Results and Lessons Learned
4
Objectives
• To be Compatible with FTA Guidance and
Recommendations
• To Test the Semi-Independent Ridership Forecasts (QC
Model) for New Starts
• To Compare the User Benefits between a Locally
Developed Transit Skim/Mode Choice Model and a
Quality Control Model
5
Mode Choice Model at
NCTCOG
• Model Structure
– Nested Logit Models for HBW and HNW
– A Multinomial Logit Model for NHB
• Stratified Sample Data
– 1996 Household Travel Survey
– 1996 FWTA On-Board Survey
– 1998 DART On-Board Survey
6
Validation: YR1999
1999 Rail Station Ons and Offs (Weekday)
8,000
300%
Observed
250%
Estimated
Number of Points:23
Error
Total Observed: 39700
Total Estimated: 39278
Overall Error: -1%
R^2: 91.42%
RMSE: 26.74%
0% Error
5,000
200%
150%
0%
1,000
-50%
Rail Station
WEST
PARK*
AKARD
WESTMORELAND*
PEARL
ST. PAUL
LEDBETTER*
LOVERS LANE
8TH *
UNION_1
-100%
MOCKINGBIRD*
CEDARS
DALLAS ZOO
VA HOSPITAL
CONV.
MORRELL
TYLER/VERNON
0
ILLINOIS*
2,000
HAMPTON*
50%
KIEST*
3,000
UNION STATION_2
100%
S. IRVING TC*
4,000
MEDICAL MKT.
Passenger volumes
6,000
Error
7,000
7
Validation: YR2005
Comparison
TRERidership
Ridership:between
2005
Comparison of
of Daily
Daily TRE
Observed
NCTCOG
2005 vs.
Observed
FTAModel
and DFWRTM
10,000
9,164
9,000
8,000
7,872
Ridership
7,000
6,000
5,000
4,000
2005 Observed
3,000
2005 DFWRTM
2,000
1,000
2005 Observed
2005
NCTCOG
2005
DFWRTMModel
8
Validation: YR2005
(cont)
of TRE Total ONs and OFFs by Station Between
2005Comparsion
TRE Rail
Station Ons plus Offs (Weekday)
2005 Observed FTA and COG Model
5500
200%
Number of Statistics: 9
Total Observed: 15,744
Total COG Model:
18,328
Overall Error: 16%
R^2: 69.07%
RMSE: 46.83%
5000
4500
150%
4000
100%
50%
2500
Error
Observed
3000
COG Model
Error%
Series4
2000
0%
1500
1000
-50%
500
Union Station
Centerport
Medical Market
South Irving
FW ITC
Richland Hills
Hurst Bell
-100%
West Irving
0
T&P
Total ONs
3500
Station
9
Mode Choice Model
(cont.)
• Nesting Structure for HBW
10
NCTCOG Mode Choice
Model Structure
• Nesting Structure for HNW
11
Standard Nesting
Structure in SUMMIT
motorized
walk
auto
transit
trn/walk
trn/drive
= composite price
= composite price
for New Starts
bus
rail
bus
rail
12
Coefficient Comparison
HBW
HNW
NHB
QC Transit (Non-Commuter Rail)
-0.0250
-0.0125
-0.0250
QC Commuter Rail
-0.0200
-0.0100
-0.0200
NCTCOG Auto
-0.0550
-0.0110
-0.0110
NCTCOG Transit
-0.0250
-0.0070
-0.0070
QC Transit
2.0000
2.0000
2.0000
NCTCOG Transit
2.5600
7.5714
5.1429
QC (in 2006$)
$6.00
$3.00
$3.00
NCTCOG Auto (in 1999$)
$5.91
$4.07
$3.30
NCTCOG Transit (in 1999$)
$2.73
$1.94
$2.10
IVTT Coefficient
OVTT/IVTT Ratio
Implied Value of Time, $/Hour
13
Quality Control Model
• FTA Recommends the Quality Control Alternative for a
Commuter Rail New Starts Project in DFW Area
• Incremental Logit Model

P0  f ( X 0 )
P
X1  X 0   X
P1  P0 
f ( X )
X
X
P1
P0
Gradient ΔP/ ΔX
ΔP
ΔX
X1 X0
X
14
QC Model Coefficients
Variable
HBW
HNW
NHB
Transit (non-commuter rail) IVTT
(minutes)
-0.0250
-0.0125
-0.0250
Commuter rail IVTT (minutes)
-0.0200
-0.0100
-0.0200
OVTT Including Drive-Access
Time (minutes)
-0.0500
-0.0250
-0.0500
Number of transfers
-0.1250
-0.0625
-0.1250
Fare (cents)
-0.0025
-0.0025
-0.0050
OVTT/IVTT Ratio
2.0000
2.0000
2.0000
$6.00
$3.00
$3.00
VOT
15
Impedance Weight for
Transit Skim
Impedance
Weight
IVTT for Transit (Non-Commuter Rail)
1.0
IVTT for Commuter Rail
0.8
OVTT Including Drive-Access Time
2.0
Number of Transfers
5.0
Fares (Peak / Off-Peak)
0.1/0.2
VOT (Peak / Off-Peak)
$6.00/$3.00
The Weights are Consistent with Mode Choice Model Coefficients
16
QC Model Flow Chart
Start
Base Case Transit System
Alternative Case Transit System
Transit Skim Using FTA Recommended Parameters
NCTCOG Travel Demand Model
Base Skim Matrix
Alternative Skim Matrix
FTA Coefficients
Difference Matrix: Skim Variables, Utilities
Base Case Matrix:
Transit Trips, Utilities
Alternative Case Matrix:
Transit Trips, Utilities
En
d
17
QC Model Procedure
• Run NCTCOG Skim and Mode Choice on Base Case to
Obtain Base Case Transit Trips and Utilities
• Run Transit Skims on Base Case and Alternative Scenario
Using FTA Recommended Weights
• Calculate IVTT, OVTT, Fare, as well as Utility Differences
between Base and Alternative Transit Skims
• Calculate Transit Share Change due to Skim Differences and
Obtain the Transit Trips for Alternative Case
• Two QC Models are Tested: One with No Rail Constant, One
with a 12-minute Rail Constant
18
Transit Skim Settings
• Maximum Trip Cost
• Maximum Number of Transfers
• Maximum Walk/Drive Time
• Maximum Initial/Transfer Wait Time
• Combination Factor
19
Comparison Results
20
Base: Express Bus
21
Alternative: Rail
22
User Benefit Comparison
• Tested One Market Segment of HBW Trips: H23WVLTP
• Compared Three Scenarios: NCTCOG Model, QC Model with No
Rail Constant, QC Model with a 12-minute Rail Constant
Auto
IVTT
Transit
IVTT
Total User
Benefit (min)
NCTCOG Model
-0.055
-0.025
43,809
QC Model with No Rail Constant
-0.025
-0.025
16,128
QC Model with 12-min Rail
Constant
-0.025
-0.025
17,261
Scenarios
23
User Benefits: NCTCOG
Model
24
User Benefits: NCTCOG
Model (cont)
25
User Benefits: QC Model
without Rail Constant
26
User Benefits: QC Model
without Rail Constant (cont)
27
User Benefits: QC Model
with 12-Min Rail Constant
28
User Benefits: QC Model
with 12-min Rail Constant
(cont)
29
Transit Trip Comparison
Transit
Drive
ΔTransit
Drive
Transit
Walk
1,771,104
47,912
NCTCOG Model
1,771,104
48,801
889
15,960
270
QC (No Rail
Constant)
1,771,104
48,180
268
15,721
31
QC (12-min Rail
Constant)
1,771,104
48,242
330
15,722
32
Base - NCTCOG Model
Alternative
ΔTransit
Walk
Total
Trips
15,690
30
Transit Walk Trip
Differences: NCTCOG
Model
31
Transit Walk Trip
Differences: QC Model (No
Rail Constant)
32
Transit Drive Trip
Differences: NCTCOG
Model
33
Transit Drive Trip
Differences: QC Model with
No Rail Constant
34
Conclusions
• QC Model Approach Offers a Level Playing Field to
Compare New Start Projects across the Country
• Transit Trips and User Benefit from QC Model is Much
Less than Those from NCTCOG Model
• Though Different in Quantity, We Observed Similar
Patterns in Transit Trip Shifts, Especially for Transit Walk
Trips, from Both Approaches
35
Next Steps
• More Tests to Confirm the Implementation
Procedure
• Investigate Transit Skim Differences
• Investigate the Impact of Differences in Transit
Accessibility between Base and Alternative
Cases
36