Colas Ensign — Covid-19 Resilience Simulator


Colas is a world leader in the construction and maintenance of transport infrastructure, including roads, railways, airports, ports and urban developments. Colas operates in over 50 countries on five continents.

In 2004, Portsmouth City Council (UK) awarded Ensign, a Colas subsidiary, a pathfinder 25-year private finance initiative (PFI) contract to manage its highway network. The Portsmouth Highway PFI is an ISO 55001 certified asset management project and is now in its 17th year.

Context and problem

Ensign is committed to carrying out critical operational activities under the project: highway maintenance, winter maintenance, network management, street cleaning, electrical maintenance, grounds and arboricultural maintenance.

To prepare for potential impacts of Covid-19 on its workforce and the service delivery, Ensign has developed contingency plans, with portfolio of actions and trigger points, including fall back activities (degraded mode) and teams reshuffling based on employee skill sets.

Ensign wanted to assess the effectiveness of its contingency plans. Considering the numerous different possible situations, designing the best reorganization for each situation was beyond their capabilities.

To meet this need, Ensign called on the LocalSolver team's expertise to develop a custom software solution using a Monte Carlo approach to simulate hundreds of cases, covering a wide range of incidence rates. For each case, the optimal team organization is computed in a couple of seconds.


Key figures

190 personnel delivering 60 activities with 180 roles and 22 alternative regimes



For each simulated case, the optimizer computes the assignment of employees to tasks while satisfying constraints and optimizing objectives as defined below.



  • Every person has a limited capacity of 5 shifts/week
  • Each activity has a role hierarchy of assignments
  • Each activity has an acceptable effectiveness threshold
  • The minimum increment for resource assignment is 0.5 shifts/week


  • Maximize total effectiveness
  • Minimize total assigned secondary resources
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Custom simulation optimization software

The turnkey software, conveying the Ensign teams' level of resilience, is cross-platform with an input and output connection to an Excel database. It is capable of performing several simulations in parallel. Each case is solved optimally in a few seconds, 1,000 simulations in 25 minutes on a laptop.

Scatter plot
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Why LocalSolver

Thanks to the unique know-how in development and software integration with a strong scientific component, LocalSolver optimization experts could offer Ensign the turnkey solution perfectly adapted to their needs. The simulator, delivered in a few weeks, solves each problem to the optimum. Dedicated and responsive support provided by LocalSolver experts remains available to provide updates to the simulator.


LocalSolver was first in mind, given our long-standing relationship and their recognised expertise in operational research, when we wanted to quantify our resilience to COVID-19. Within two weeks of our initial brief, LocalSolver provided us with an optimisation tool that was further customised, demonstrating excellent client care with prompt response to request. I warmly commend LocalSolver for fostering an outstanding working relationship and delivering advanced numerical solutions: they are formidable!

Eric Brangier, Ensign Managing Director, Colas Group

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