Information on Route Selection Method

Hi, I have been using cycle.travel for a number of years and am tremendously grateful for the amazing service it provides. I use it for everything from quieter ways to navigate my city to planning the route for bicycle touring.

I apologise if this has been asked before but I have not found it on the website

I have been thinking recently of how the algorithm chooses particular routes. Would you be able to provide some information on this? I understand some of this may be proprietary, in which case a high level description would suffice. I think it would be useful to understand the assumptions/limitations of the software to inform my own route mapping.

Thanks

Neil