Why Colas chose Hexaly to develop their 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. In 2020, To prepare for the impacts of Covid-19 on its operations, Colas called on Hexaly’s expertise to develop a Covid-19 Resilience Simulator.

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 the potential impacts of Covid-19 on its workforce and service delivery, Ensign has developed contingency plans, with a portfolio of actions and trigger points, including fallback activities (degraded mode) and team 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 Hexaly 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.

Input data

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

Covid-19 Resilience Simulator: a 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, with 1,000 simulations in 25 minutes on a laptop.


Why Hexaly?

Thanks to the unique know-how in development and software integration with a strong scientific component, Hexaly’s optimization experts could offer Ensign the turnkey solution perfectly adapted to their needs. The Covid-19 Resilience Simulator, delivered in a few weeks, solves each problem to the optimum. Dedicated and responsive support provided by Hexaly experts remains available to provide updates to the simulator.

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

Eric Brangier Ensign Managing Director, Colas Group

Please look at our customers‘ webpage to discover more case studies in various industries. Are you interested in trying it out? Get free trial licenses here. In the meantime, feel free to contact us; we will be glad to exchange your optimization problems.