SATURN User Group Meeting: Epsom, October 14 2004

• Presentation by Dirck van Vliet

SATURN 10.5: NEW FEATURES

• Release of Origin-based Assignment

• Better Simulation-Assignment Convergence

• Improved understanding and reporting of very poor convergence

• Improvements in SATME2

• Specific Program Upgrades

10.4 BUGS (A)

• Matrix cordon crashes (1)

• Rotational shift in graf.dat (2)

• Incorrect speeds in DA code 4053 (8)

• ROSIE refuses to work! (9)

• The speed-flow elasticity ‘g’ corrected in both 10.4 and 10.5 (15, 42)

• Programs with missing segments (19,20)

10.4 BUGS (B)

• SATALL command line problems with FRREZE and ICING = T (26)

• SATALL problems with MASL n (28,29)• Various problems under PASSQ when

flows enter/leave at the “wrong” ends (33)• SATNET – use of lower case ‘c’ (36)• SATNET – PASSQ and UPDATE together

(39)

10.4 BUGS (C)

• Incorrect entry/exit flows on simulation links with UPBUS = T (36)

• Potentially major problems with highly congested networks involving MAXQCT and PASSQ (41)

• SATALL: Problems in delays calculated under PASSQ when the proportions of traffic within shared lanes changes (38)

Origin-Based Assignment (OBA)

• Full release in 10.5

• Supplementary fee structure

Origin-based solution

16

9

5

2

6

8

1

3 4

10

7

181112

19

17

15

22

14

21

23

2413 20

2600 (.060)

1600 (.040) 800 (.07)

2500 (.057)

3000 (.097)

3200 (.023)

4500 (.043)

6200 (.040)

2500 (.066)

2200 (.147)

485 (.107)

415 (.020)

915 (.055)

800 (.137)

400 (.163)

15 (.032)

489 (.118)

11 (.122) 389 (.042)

300 (.04)

300 (.043)

1400 (.030)

900 (.177)

311(.037)

300 (.137)

node

used link

Legend

flow (cost)

13

0.0001

0.001

0.01

0.1

1

10

100

0 20 40 60 80 100 120 140

CPU time, seconds

Rel

ativ

e ex

cess

cos

t, p

erce

nt

OBA

FW

  

0.0001

0.001

0.01

0.1

1

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0 100 200 300 400 500

CPU time, seconds

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OBA

FW

Figure 2: Convergence results for a network of York 

Practical Advantages of OBA

• Comparable cpu to Frank-Wolfe.

• Efficient data storage (RAM)

• Improved accuracy (especially for small network/matrix changes)

• Route flows may be analyzed exactly for, e.g., select link analysis

• Permits “warm starts”

OBA Restrictions

• Multiple User Classes (directly)

• Elastic Assignment (directly)

• SATPIG

• Cordon matrices in P1X (but OK in SATCH)

OBA Examples

• Headingley buffer network: Add 1 trip

• York network: Add 1 lane

• “Inkton” – Optimize signals

P1X (A)

• Link annotation choices sub-divided (3)

• Maximum transient queues (4)

• Continued improvements in PMAKE (5)

• Reduced intensity .bmp files (14)

• GIS curved links as “arcs” (18)

• .Dat files updated from SIGOPT or SATOFF = T (20)

P1X (B)

• Multiple crossings in SLA (26)• UC Flows explicitly listed under link

annotation (27)• Node line drawings properly scaled (28)• Improved choices for bandwidth colours

(30)• More logical defaults for data from missing

links(32)

P1X (C)

• Blocking back factors annotated as 1-BBF (41)

P1X – Convergence Menu

• New “top menu” entry

• Includes new forms of convergence information:

• Changes to blocking back factors

• Network summary / comparisons

• 10 worst converged nodes, flows and delays

MX

• New batch file MXWEIGHT to combine matrices (e.g., within external demand-supply loops)

SATNET

• U-turns for buses more realistic (3)

• New checks/input options under KNOBS (4-7)

• Blank lines now ignored (mostly) (10)

• Lane-disciplined roundabouts (to follow)

SATALL

• AUTOK still there!

• Better identification of simulation link flows with UPBUS = T (6)

• Various minor changes in the way simulation cost-flow curves are estimated

Simulation (A)

• Blocking back no longer applies in certain circumstances (4)

• Random delays may also be applied to “minor” movements (6)

• Minimum iterations – NITS_M ()

• Exit/entry flows on sim links are better differentiated with UPBUS = T

Simulation (B)

• Queued delays in over-capacity shared lanes are rigidly controlled by their combined V/C ratio (7)

• Particularly significant with PASSQ flows (8)

• Tighter controls of lane sharing (9)• “Between-node” simulation convergence

monitored separately (11)

Assignment

• Minimum number of iterations –NITA_M (1)

• MAXQCT now used in the assignment as well as the assignment (2)

SATME2

• Extra documentation (1)

• Extra warnings (2-4)

• .ME2 files allows P1X to display, e.g., Xa factors

• Options to combine counts together (e.g., as screen lines) (8)

SATOFF / SIGOPT

• Batch file now runs SATOFF and SATSIM automatically (1)

• NIPS parameter in SATALL limits the number of optimisations

SATCOBA

• Add link flows from multiple “networks” (1)

• Link turning proportions added (2)

• Common link numbers for different networks (6)

Super Convergence Tricks

• Use OBA for the assignment

• Use AUTOK

• Use NITA_M and/or NITS_M

Networks Behaving Badly; Why?

• Badly congested in future year

• Badly coded do-minimum networks

• One-lane roads with multiple turns

• Excessive blocking back with “feedbacks”

• Incorrect use of MAXQCT

• External traffic that cannot enter the network

SATEASY Demand Models

• “Separable” demand functions by o-d

• Limited number of demand formulae

• Incorporated internally

• Optimum convergence

“Full” Demand Models

• Includes interactions between o-d’s, e.g., distribution

• Potentially extremely complicated combination of individual blocks

• Very large number of potential structures• Some structures (e.g., hierarchical logit)

may be optimised• But …

Demand Model Components

• … individual components are based on standard matrix and/or vector manipulation

• Can be set up using: MX, EXCEL, CUBE (Trips) … or DIADEM

• Onus is on the modeller to choose the appropriate structure + parameters for their particular study

VaDMA / DIADEM “Concerns”

• VaDMA is not sufficiently prescriptive

• DIADEM / SATURN interface

• DIADEM may not satisfy “basic” VaDMA recommendations

• Insufficient testing using real studies to verify the VaDMA scoping spreadsheet or to provide a “good” example.

            

Figure 7.6: A (convergent) cobweb set of demand/supply iterations 

C

c(1) A

E D

B C

s(T)d-1(T)

T

 

Fixed Step Length Supply – Demand Equilibration (FSL)

• General method for equilibration between demand models and supply (SATURN)

• Take weighted average of “current” and “next” demand-generated trip matrix with a constant weighted average.

• Good guess: lambda = 1 / (1 + e)