IRSE 2007 Technical Conference- Brisbane

Application of Problem Space Search to Heavy Haul SchedulingAlex WARDROP & David CALDWELL

04/12/232

What is scheduling?

“Scheduling” is a broad term and can include crew rostering,

maintenance scheduling and train planning (timetabling)

Here the main interest is train planning

Train plans may be developed around the constraints of crew rostering,

and in cooperation with maintenance scheduling

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Train Planning

Train planning is placing a set of train requirements over a railway

network

Train requirements are the trips that train operators want to operate

over a given period of time to meet commercial requirements (moving

stuff)

The aim of the train planner is to move these trains to their required

destinations with as little delay as possible

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Train Planning

Train planning Maintenance scheduling

Crew rostering/ industrial requirements

Train demand (e.g. trains, origins, stops,

destinations)Maintenance requirements

Day of Operation planning

Operations

Maintenance

Other Constraints

Network (e.g. running times, loop lengths, safeworking,

loader capacity) Train performance and requirements

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Developing a timetable

In a manual process, the highest priority trains are “drawn” on the plan

first

Lower priority trains are stopped for passes in preference to stopping

high priority trains

• Order of priority- “two legs, four legs, no legs”

This means that passenger trains go through the route on the minimum

running times

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The heavy-haul problem

While the most densely utilised heavy-haul lines are double track, the

majority of Australia’s heavy-haul track mileage is on single-track line

A major challenge is figuring out how to stop and pass trains, and when

to admit them to the next section This has to be done with consideration for

both safeworking requirements and

refuging opportunities

A train plan looks like this, showing the

train ID and stops

Lines are coloured to represent an

important attribute, like train length,

running time, or priority Dist

ance

Time

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What is Problem Space Search?

Unlike a mathematical algorithm which seeks to find an exact solution,

Problem Space Search employs a heuristic (or trial and error

mathematical process) to develop many feasible solutions to a problem

These solutions can then be scored against an objective function and

ranked

Research undertaken jointly by the University of South Australia and

the former TMG International found that the technique was applicable to

rail scheduling

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Application of Problem Space Search

By applying perturbations to crossing delays of trains moving through a

network, the order in which trains meet is varied, and so the orders of

crossings changed

Thousands of different valid train plans can be generated in a matter of

seconds

These valid solutions can then be evaluated and ranked for their

performance against criteria such as delays and cost

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Application of Problem Space Search

Developing a timetable by manual techniques generally takes months

An automated train plan optimising technique has obvious direct

benefits for train planning, reducing the time to produce a timetable,

and improving its “quality”

The huge reduction in the effort required to develop a timetable means

that timetables can be quickly manipulated very close to the

implementation horizon, and still produce optimal results

Timetables can also be easily developed for speculative purposes

(“what if…” scenarios)

Software using Problem Space Search for these purposes has been

developed

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Line Capacity report

Near-optimal timetable

RailSched

Information flow

RAIL NETWORK DESCRIPTION

Track layoutRefuge locationsJunction locationsSectional running timesSafeworking systems

TRAIN CHARACTERISTICSLengthRunning time classPriority INPUT TRAIN REQUIREMENTS

Nominal despatch timesDays of operationDwell timesDependencies between services

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Typical Inputs

Track Infrastructure- links and nodes

Bi-directional line

Uni-directional line

Refuge

Crossing loop

Crossovers

Station name

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Output: optimised train plan

BW4 is a high priority train

MB3 is a low priority train

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Output: Capacity utilisation

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Application

The Problem Space Search technique is applied for both timetabling

and strategic infrastructure planning

An integrated scheduling system, ScheduleMiser ™ was developed for

BHP Billiton

A more general scheduling tool, Rail//Sched ™ is the subject of

ongoing development for the Australian Rail Track Corporation

In both cases the general data requirements and outputs are the same,

thought the interfaces differ significantly, according to specific

requirements

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Case study: ScheduleMiser

ScheduleMiser was developed to represent BHP Billition’s iron ore

moving process, rather than looking at trains in isolation

Time it takes to load a rake

Time it takes to re-stack the stockpile at the loader

Desirability of different rake configurations

Material at mine loader

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Translating BHP requirements

The user specifies production requirements, as well as other

operational variables like loader availability and rake locations

ScheduleMiser builds trains of one, two or three rakes to satisfy

production

Day to day operational conditions, like TSRs and track possessions, are

also configured

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The BHP requirement

Rolling stock, mine, unloader and network

configuration

Ore requirements at Shipping port

Optimised timetables and train plan

Rake reportDumper report

ScheduleMiser

Track availability (possessions)

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Typical schedule output

The user configures all the requirements and runs the schedule

resolver

A train plan, similar to the following, is resolved

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Planning close to the horizon

Need to be able to rapidly review timetable for changing train

requirements, e.g. out of order running

Developing amended timetables close to the event

WorleyParsons, with the assistance of a Commercial Ready grant, is

currently integrating automated scheduling with real-time GPS train

location information

Train locations can be continuously updated in the model, and a

timetable with minimum delay calculated almost immediately

There is another significant application of automatic timetable

generation…

04/12/2320

Strategic Infrastructure Planning

Why different scheduling scenarios need to be considered

• Which loops should be lengthened or moved?

• Will changing the safeworking system (i.e. eliminating token

exchange delays) have a practical effect on capacity?

• Will automating points (and reducing route-setting delays) and

improving turn-out speeds have a practical effect?

• What is the effect of running some longer trains which are excluded

from more loops?

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Considering the future

DEMAND SCENARIOS

SCHEDULING

WHAT IS THE MOST COST - EFFECTIVE?

INFRA - STRUCTRE

TRAINS

OPERATIONS SCENARIOS

DEMAND SCENARIOS

SCHEDULING

WHAT IS THE MOST COST - EFFECTIVE?

INFRA - STRUCTRE

TRAINS

OPERATIONS SCENARIOS

04/12/2322

Case Study: Rail//Sched

The ARTC is developing its network for expected traffic growth

Their 2005 Hunter Valley strategy anticipates that from 2006 to 2010,

tonnage between Musswellbrook and Antiene will approximately triple

from about 20MTpa to about 60MTpa

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Hunter Valley growth

From

ART

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05 H

unte

r Val

ley

Coal

Net

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Cap

acity

Impr

ovem

ent

Stra

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, fig

ure

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ii

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The effect of growth

ARTC developed infrastructure improvement plans to satisfy this growth

To verify that delay would remain at an acceptable level, ARTC

developed proposed infrastructure schemes (varying over time), and

then developed experimental future train requirements to meet

operators’ train requirements/ tonnages

ARTC then used Rail//Sched to generate hypothetical timetables for the

increased network usage

Once these timetables were generated, they were assessed for relative

changes in delay compared with current operations

04/12/2325

ARTC’s application

Expectedly, when traffic

levels increase, but the

network remains

unchanged, average

delay per train and travel

times increase

The process applied to

assess infrastructure

improvements…

Describe infrastructure scenario (s)

Develop input timetables (train types and despatch times of projected traffic)

Optimised timetables Average Delays

Post processing (Excel)

RAIL//SCHED

Pre-process (add noise to despatch times)

Normalised dimensionless delay

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ARTC’s application

The types of network variables that are typically considered are

safeworking, loop lengths, loop locations and additional tracks

One component of ARTC’s strategy to meet projected demand is the

Antiene to Grasstree duplication

Duplication by 2008, proposed in the strategy, reduces delays to below

the levels in early 2006

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Modelling delay

Modelled Hunter Valley Network Performance

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MB

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MB

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WH

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CA

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0

5

10

15

20

25

30

35

Ex

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(dim

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sio

nle

ss

tim

e)

4th quarter 2006

1st quarter 2007

2nd quarter 2007

3rd quarter 2007

4th quarter 2007

1st quarter 2008

2nd quarter 2008

NEWCASTLE MUSWELLBROOK

Delay per train reducing in first half of 2008

Duplication of Antiene - Grasstree in first half of 2008

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Benefit for planning

Being able to quickly generate these speculative train plans (and

calculate delay) is very helpful for considering

• Whether a proposed infrastructure plan is a going to satisfy

requirements

• Which projects should take priority

• Whether changing traffic demands will adversely effect delay (and

operators’ costs)

04/12/2329

Conclusion

Scheduling is at the core of railway operations

Train plans which reduce the amount of delay per train improve the

capacity and efficiency of the railway

Optimisation of train plans by application of the problem space search

technique is much faster than manual techniques

Computer generation of train plans makes it possible to experiment with

effects of train and infrastructure changes, and assess the usefulness

of capital projects