Deeplinks for carpooling lines

### Introduce yourself

I am working at [Ecov](https://www.ecov.fr/), a french company building carpooling lines (as public transport lines, but vehicles are usual drivers doing their own trip). We are describing our carpooling lines with GTFS files but this standard does not fit completely.
Exemples of our GTFS files :

[M Covoit Lignes+](https://transport.data.gouv.fr/datasets/horaires-theoriques-des-lignes-m-covoit-ligne-plus?locale=en) in Grenoble
[Covoitici Plain de l'Ain](https://www.data.gouv.fr/datasets/lignes-de-covoiturage-covoitici-plaine-de-lain) near Lyon
[Grand Est](https://www.data.gouv.fr/datasets/lignes-de-covoiturage-covoitici-grand-reims-mobilites-covoit-region-grand-est/) (Metz et Reims)
[Héléman](https://www.data.gouv.fr/datasets/lignes-de-covoiturage-heleman/) near Genève
We have a need for a dedicated route_type (see https://github.com/google/transit/issues/430), and for a better description of uncertainty (see https://github.com/google/transit/issues/599), but here we have an other question :

### Ask a question

We need to give rooting result to the end user, but with a link towards our application.
**Do you know what would be the best practice to give this link or deeplink?**

In most of case, a simple link towards our app would be enough (as it will address essentially new users, who will need to download and subscribe), it would be useful to give them a deeplink. Thus, once having subscribed, they could be linked directly in the app on the good page, with the specific trip already prepared.

**Do you have any advise or exemple of deeplinks shared at the end of the rooting results builded with GTFS?**
Using which field in the GTFS spec? (booking rules.txt / booking_url? - but we need a specific booking_rule_id for each trip - or route_url? or outside of the GTFS?)

Regards,