Ferry trips

Good morning,
It’s impossible to have in many cases a correct trip by car between 2 towns separated by the sea when the possibilty to use a ferry has a shorter transport time than by road.
For example:
Transport from Portsmouth (Uk) to Ouistreham (France).
Normally it takes by car with the ferry around 6 hours while by road with openstreetmap it takes 8 hours or more.
Openstreetmap ignore in this case the trip by ferry.
Could you give me an explanation why we can’t use the ferry?

Thank you in advance.

Remark :with waze application there is no problem.

OpenStreetMap is “just” free geographic data, used by many apps.

¿Which OSM based app are you refering to?

Whatever the use of Graphhopper or OSRM independantly of an OSM data application we have this problem. My OSM data application is Magic Earth and the result is the same.

Perhaps my understanding of geography is wildly incorrect, but I always thought there wasn’t a road from the UK to mainland Europe. Has a bridge been quietly built across the English Channel?

The shorter time to go from Portsmouth to Ouistreham is to take the ferry between these towns that starts in Portsmouth

Ferry routes can be mapped in OSM and I was under the impression that at least some routers could use them.

Is the ferry route between Portsmouth and Ouistreham mapped in OSM? That should include any service roads, etc. that connect the land highway system to the ferry route.

There are no auto carrying ferries in my area but I have heard that there are some well mapped examples in the Puget Sound area. https://www.openstreetmap.org/#map=12/47.5630/-122.4534 Maybe you could use those for examples and see if the ferries in your area are similarly mapped.

I see https://www.openstreetmap.org/way/420041114

  1. has no ferry attribute.
  2. is connected to another roads via highway=service.

So some routers:

  1. could not find on ferry any replacement for highway tag to make it routable
  2. could not route on service roads. Especially for far distance

Those both sound like failures of the router, not problems with the data. The tags route=ferry and motor_vehicle=yes should be sufficient to indicate to a router that this is a car ferry. It’s also normal to have to drive on a bunch of service roads within a ferry terminal. It sounds like bugs need to be reported with the respective routers so they can fix their rules to cover these situations.

could be sufficient

I think route=* has been invented to allow to map a class or importance of the way. Is the ferry is so omportant as trunk or jast as service? This is very important for routers

In the current OpenStreetMap so it’s impossible by car to have the correct trip (shorter transport time) between Portsmouth and Ouistreham (by using for example OSRM) which is not the case with google earth or waze that use the ferry trip.
Accordingly the OSM based applications aren’t correct when the shorter transport time has to be done by ferry.

I agree. However, it seems like the routers are assuming too low of an importance for ferries where this tag hasn’t been used. It would still be a good idea to let them know so they can make adjustments.

motor_vehicle=yes (or motor_vehicle=no) is legal access rules
motor_vehicle=yes is not enough on the road we should set highway=*

ferry is just the same case

So I always set appropriate ferry=*

As for giver ferry I think it is better to set something like ferry=secondary (or at least ferry=tertiary) because a road between two countries is rather important one.

So we also see that the service roads should be remapped to higher level because it is intended for some transit traffic to another country.

From memory with odd routings in the Scottish islands years ago the duration=* tag is far more important than the ferry=primary|secondary|tertiary. There are numerous examples of ferries accessed by service roads with minimal access tagging which work with Graphhopper in the same area.

Duration is indeed the problem here. Portsmouth-Ouistreham is routable, it’s just that it’s a 6hr trip (vs 3hr for Portsmouth-Cherbourg) so the routers prefer to go via Cherbourg. You can drag the points to halfway along the ferry and see that it’s happy to go that way, until the distance becomes shorter via Cherbourg so it starts snapping that way.

It’s a bit arbitrary anyway as ferry routing is of limited use without timetable information, which we don’t have.