Motorways are access controlled highways with designated points of entry and exits. Missing an exit on a motorway can result in long detours of tens of kms to get back to that point. In OSM we tag the exit nodes on the highway as highway=motorway_junction with a ref tag indicating the exit number that is displayed on the road signages.

According to the OSM wiki, motorway junctions should have a unique ref indentifier or name. In the US alone there are around 7,000 exits without a ref identifier. Many exits have no official idetifier and they are usually tagged with an additional noref=yes. What about the rest? Are they missing a ref or does it not have one?

screen shot 2016-04-05 at 4 48 50 pm Overpass query to find exits without a ref or noref=yes

Here’s how you can investigate the missing ref on motorways in your area:

Find exits without a identifier

There are multiple ways to do this:

  • Run this Overpass Query for your area to see where to focus your effort
  • Use Check Autopista 2 to analyze a specific motorway for missing information
  • Use this tms background layer in JOSM or iD tms:{zoom}/{x}/{y}.png?access_token=pk.eyJ1IjoicHJhdGlreWFkYXYiLCJhIjoiMTA2YWUxNjRkNmFmZGQ4YzAxZWFiNDk0NDM1YjE1YjAifQ.4P6N5dNmA_WQXd3BsJvu5w to spot exits with missing ref tags (blue dots)

  • Red dots are exits with a ref
  • Red lines represent motorway_link
    screen shot 2016-04-05 at 4 48 50 pm

Find a source for the exit number

The recommended approach is to survey the location yourself for the correct information. If you are short of cash to travel all the way, there are some armchair resources:

Add the missing data

If you find an exit number, then use ref=* tag to add it to motorway junction. If there is no exit number and the sign board has exit or nothing written on it then add noref=yes tag to the motorway junction.

The Mapbox data team is currently mapping the missing exit numbers in the USA using this workflow. Our progress and observations are documented here. Feel free to join in and give us feedback on how this can be improved.

Comment from SomeoneElse on 5 April 2016 at 14:28

On countries that don’t use junction reference numbers as much as some others (like the US), I wouldn’t expect too much from a query looking for junction reference numbers; just the same as in the UK (where there aren’t multiplexed routes) I wouldn’t expect to be able to extract sensible and complete route relations.

Just because the wiki says to do something it doesn’t mean it’s commonly done or even a good idea; sometimes it represents only the view of the person who last updated that wiki page.

In the US I’d spend time on misaligned and mismapped TIGER data before even thinking about whether a nonexistant junction reference number is indicated by “noref=yes” :)

Comment from Baloo Uriza on 5 April 2016 at 16:45

I’m still of the opinion that ref=* on the highway=motorway_junction isn’t cutting the mustard.

  1. While exit numbers are required in interstates, they’re not yet widely rolled out on any other American network. And even then, some states have opted to stop signing an interstate rather than go back through and (re)number the exits. California debated this with Interstate 5 for it’s nearly thousand-mile portion; Oklahoma stopped signing I 444.

  2. What side is the exit on? junction:ref=* and destination::=* nails this fantastically on the departure segment of the exit, and what I’ve been focusing on when I map motorways in Oklahoma that have exit numbers. Oklahoma’s a relatively straightforward example, since only a dozen exits aren’t to the right, statewide. But I’ve tried mapping places with more complex edge cases: What happens when you have center exits? What happens when you have an even number of lanes, and lanes 1, 2 and 4 go through, but lane 3 is an exit? Where’s it go? What’s it signed as being an option to get to? What if it’s an exit when the motorway is going one way and an entrance when it’s going the other? The node tagging just doesn’t capture this except in the most ham-fisted possible way.

  3. Node tagging for this already lost. Data consumers aren’t consuming motorway_junction because it’s ambiguous for the first two reasons. But at a minimum, osmand announces destination=* and destination:ref=* along with the direction of the turn:lanes=* or turn:lanes:= direction for the most likely lane.

Comment from jinalfoflia on 13 April 2016 at 06:15

@SomeoneElse @paul Johnson Thank you for the comments. These are valuable suggestions and we will keep this in mind while going forward towards the next projects. For now, our focus is only towards adding missing exit numbers on the motorway junctions and then following it up with addition of the missing destination=* tags.

Comment from BladeTC on 16 April 2016 at 19:11

Very good brother! The background is working well in JOSM.

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