Challenge 3: Health and Safety

For this challenge, we are going smaller and more detailed. In most projects, health and safety is a major consideration, but often the schedule doesn't have such a big impact. Not so in this example - H&S is a key source of scheduling constraints, and they are interesting! I've included a more detailed description below, and also some hints on how to work with these constraints.

This competition is a simplified model of a project we recently supported, and it is rare in that the initial solution was developed by hand - this means that you don't need a bag of algos to win this one, the (what I think!) optimal solution can be found by hand in a reasonable amount of time (maybe a few hours, once you've got your head around the problem).

Competition Prizes

• 1st place: $400
• 2nd place: $200
• 3rd place: $100
• Best new submission: $100 (reserved for a first-time competitor)

Planlab Workspace

A Planlab workspace was available for the challenge. Competitors could upload XER files with their solutions or create solutions by hand. The workspace included these time-location visualisations to help build intuition for the problem:

• Viaduct: time-location chart, showing the work on both carriageways
• Combined: time-location and resource histograms

If you want to see how one of those charts gets built in the first place, we later handed the same viaduct programme to an agent and wrote up what came back in AI Creating Time-Location Charts.

Historical Submission Format

Competition entries were accepted as XER or CSV files by email with the subject "Challenge 3".

Competition Timeline

This competition ran until 17:00 UK time on 5 December 2025.

This competition is now closed. The project file and rules remain available below as an archived scheduling exercise, but submissions are no longer being accepted.

The Challenge!

Download the Project File

Download Viaduct_example.xer.zip

Rules

• Respect the XER file - all activity relationships, calendars, durations, resource limits, and resource assignments.
• Respect the Health & Safety Rules (below)
• The only changes that can be made are the ones listed in Decisions

Health and Safety Rules

This project is the renovation of a motorway overpass. The overpass will still carry traffic during the renovation, and some of the processes involve using high-pressure water to remove damaged areas of concrete. This can result in debris flying around, and means there are restrictions on how these activities can be done.

The work is split into 2 carriageways (Northbound and Southbound), and within each Carriageway is a set of Spans (the bit you drive on, also called the EVR) and Piers (the uprights that support the Spans).

The Health and Safety restrictions require that no workers are working on a Span, if there is also work being conducted on an adjacent Pier - this is due to the risk of material, equipment or debris injuring someone working on the Pier. The scaffolding and jacking sets (these are assigned to LOEs) can remain in place for the Span and/or Pier, but no work can be carried out (this includes taking down or putting up scaffolding, but excludes the Expansion Joints).

A list of the Piers and adjacent Spans:

Southbound Carriageway

Northbound Carriageway

Resource Loaded Level-of-Effort Activities

There are resource loaded level-of-effort activities in the schedule. Many of these are to track costs, but there are some that capture the use of a limited resource.

In this project, in order to repair the bearings that connect the EVR (Elevated Vehicle Roadway) to the Piers that support it, the EVR needs to be jacked up a few millimetres. This requires specially fabricated equipment (a jacking set), of which there's a limited number.

To complete the repair, a series of activities has to be carried out, and the jacking set needs to be installed before it starts, left in place while work is carried out, and then removed - this frees up the equipment to be used on the next Pier. As the duration of this work is variable, the jacking sets are assigned to an LOE.

This can cause a problem when conducting resource levelling or optimisation - when you schedule the activity that starts the LOE, you don't yet know its end → so what do you do with the resource requirement?

Bonus Constraint! Hydrodem Appliances

Historical note: solutions that did not meet this constraint were still eligible for the competition

The concrete repair work being done on each Span and Pier requires access to a specific appliance that provides ultra-high-pressure water jets to remove damaged concrete (in the schedule, these are called "Concrete trucks").

These trucks need to be in position for any concrete repair work to be done, and can be parked at either a Span or a Pier. The truck can be used by up to three Spans or Piers at the same time (but not a mix of some Spans and some Piers), and they must be next to the truck e.g.

• If you are parked at P3, then you can support P2 and P3 and P4 at the same time.
• If you are parked at S2-3, then you can support S1-2 and S2-3 and S3-4 at the same time.

There are a total of 6 concrete trucks available.

Decisions

Activity timings: the start and end dates for activities.

There are no modes for activities, and no modes for resources.

Try the Archived Challenge

The competition has closed, but you can still download the XER file above and use the rules as a scheduling exercise.