1. Transit Path-Building: “To Multipath or Not to Multipath”
David Kurth & Suzanne Childress (Parsons)
Erik Sabina & Sreekanth Ande (DRCOG)
Lee Cryer (Denver RTD)
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

2. Issues with Path-Building / Mode Choice
“The FTA advised us to do it…”
Consistency
Coherent Story
“…and it’s a good idea.”
Integrated Regional Model Concerns – DRCOG
Detailed, activity-based model – needs consistency
FasTracks, New Starts – RTD
Logical transit paths
Credible mode choice
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

3. } } The Crux of the Issue “Simple” Path-Builders & Mode Choice
All-or-nothing
Shortest path
“Transit riders don’t behave that way” led to…
“Complex” Path-Builders & Mode Choice
Multi-path
Optimal strategies
Path-finder
Multinomial Logit } }
Nested Logit
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

4. Example RTD Path Options
3 Reasonable Paths
Path 1: 2 Local Buses
Path 2: 2 Local Buses
Path 3: Local Bus, Rail, Mall Shuttle, Local Bus
Travel Behavior Inventory (TBI) observations for all three!
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

5. OK, so what’s the issue?
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

6. OK, So what’s the issue?
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

7. OK, So what’s the issue?
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

8. Decisions, Decisions Complex Path-Builder / Simple Mode Choice
Transit multi-path reliance
Simple Path-Builder / Complex Mode Choice
Transit multi-path avoidance
Complex Path-Builder / Complex Mode Choice
Just Say “NO!”
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

9. Transit Network Testing Opportunities
TBI Data –
Access and egress mode
Individual routes used
Individual choice regarding path options
RTD System
Reasonable options for paths
Reasonable options for modes
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

10. Normal Transit Network Testing
Route specific travel times
Modeled versus observed
Selected transit paths
Heuristic (“That makes sense…”)
Boardings per linked trip
Assignment of observed on-board survey trips
Comparison to observed boardings
By route
By service type
By access mode (walk versus drive)
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

11. TBI Path-Matching Experiments
Reviewed selected individual reported paths
Some logical paths not selected
Some multiple path options
Some poor reporting by respondents
Comparison to simple path-builder
Total boardings / total linked trips
By network combination (local only, premium only…)
Prediction success tables
Boardings per individual linked trip
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

12. Transit Networks for Path-Building
Local Bus Only Local & Premium Bus
Premium Bus Only Local Bus & Rail
Rail Only Premium Bus & Rail
All Modes
4 Times-of-Day:
AM Peak PM Peak Off-Peak Early/Late
2 Access Modes:
Walk Access Drive Access
56 Sets of Paths
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

13. Aggregate Path-Matching Experiments
Walk Access –
All Times-of-Day
TBI Reporting Problems – Mall Shuttle
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

14. Example Local-Rail Paths – The Good
TBI Reported Local Bus to Rail – Correct Path Found
Rail
Transfer Station
Local Bus
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

15. Example Local-Rail Paths – The Bad
TBI – Local Bus to Rail
Only Bus Path Found
Logical Bus-Rail Path Exists
Local Bus
Rail Option Here
Transfer Station
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

16. Example Local-Rail Paths – The Ugly
TBI – Local Bus to Rail
Multi-path found:
Bus Only
Bus to Rail (to Mall Shuttle)
Local Bus Path 1
Local Bus to Rail
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

17. Path-Building Experiments
Path weights to encourage mode use
Bus-rail paths reviewed
Base case:
Rail time = 0.7 x actual time
FTA OK’d for existing DRCOG model
Optional case:
Rail time = 0.6 x actual time
Pushing the FTA approval envelope
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

18. Path-Building Experiment Results
Local/Rail Paths
Base case
33/62 (53 percent) used rail
Boardings/trip should be > 2.0
Optional case
43/61 (70 percent) used rail
Boardings/trip “reasonable”
Base selected due to “previous acceptability”
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

19. How Good is the Simple Path-Builder Approach?
Prediction success tests
Built paths for observed interchanges
Based on observed mode combination
Local only, premium only, rail only…
Compared:
Modeled to observed boardings
Interchange-by-interchange
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

20. Prediction Success Results PM Work Trip – Walk to Rail Only
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

21. Prediction Success Results – Simple Path Builder
67 percent “correct”
Unaffected by access mode
IT WOULD REALLY BE NEAT TO REPEAT THIS ANALYSIS WITH “SMART” PATH-BUILDER!!!!
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

22. Prediction Success Results – Simple vs. Multi-path Builder
AM Walk Access Trips
Complex Approach
Observed trips compared to “All modes” paths
Simple Approach
Observed trips compared to same network paths
Local only, premium only…
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

23. Some Practical Issues Model Estimation Constraints
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

24. Recap Transit users Transit multi-path builders Pick individual paths
Do not necessarily pick the same paths
Do not necessarily pick logical paths
Do not necessarily accurately report paths
Transit multi-path builders
Deterministic heuristic representing discrete choice
Do not capture choice behavior
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

25. Conclusions Transit paths
Are choice behavior
Should be represented in mode / path choice
Require substantial resources to model and estimate
Common network validation measures that may not be sufficient
Ability to assign all observed trips
Matching observed boardings / linked trip
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15

26. …and Some Questions
For Simple Path-Builder / Complex Mode Choice Approach
Are there limits for path weights to “encourage” path options?
Do path-building weights need to match mode choice relationships?
Will inconsistencies impact user benefits?
May 9, 2007
11th TRB National Transportation Planning Applications Conference -- Session 15