Over at Telenav we have been busy comparing the GPS traces of drivers using our navigation apps against OSM data. This is fun work and sometimes leads to really useful results. One of our recent studies involved comparing what we think are one-way streets to the corresponding OSM ways. The process is quite simple: count how many traces following a given street go in one direction, and how many go in the other. If the number for one direction is close to zero, the street is probably one-way. The outcome depends on the confidence level you apply, but it turns out that there are more than 100 thousand OSM ways that probably should be marked with a oneway tag, but aren't.
One. Hundred. Thousand.
I don't know about you, but I think that would make for a really great MapRoulette challenge. So that's what I did, and here it is.
But how do you know if a street should be one-way without having eyes on the ground? It turns out the aerial imagery provides helpful hints. Let me show you what I look at to verify the one-way-ness of a street using just JOSM and the Bing layer.
Let's look at this case here:
Notice the arrowhead? That is the direction we found the vast majority of trips followed, so we think that is the one-way direction of this street. Let's look in JOSM:
In this case, there is really only one hint that this is in fact a one way street, but it's a pretty convincing one: The markings on the road. See the stop line? It goes all the way across, which it wouldn't if traffic were allowed to enter from the right. Also, it is a little blurry, but there is what appears to be a left arrow painted on the road as well. So all in all, I am convinced that this way should be marked oneway=yes.
Be careful though! OSM ways can be very long, and the one-way restriction may not apply to the entire way. So always be sure to check the entire length of the way before you tag and upload, and split the way as necessary! The Telenav detection works on smaller segments internally, so the suggested one-way-ness does not always apply to the entire OSM way.
Lets' look at another case.
Looks like a residential area. Let's load it up in JOSM:
In this case, it's really hard to see. There's no obvious stopping line that I could see, and there's too much shade to see if there are parked cars on the left side of the street that are parked facing west - which would be another good indication that it is a one-way street, because it is illegal in the United States to park in the opposite direction of the flow of traffic. So this one I would mark as 'Couldn't See'. Perhaps someone else sees something I don't? Here is the permalink to the task in MapRoulette. (Neat eh, permalinks - makes it easy to share a task you want to discuss or highlight. They remain valid even after a task is fixed or even deleted.)
Oh and yes, I am afraid this is another United States only challenge... We are working hard to get more international challenges in, and we already have some interest. I am sure I mentioned this before, but MapRoulette now has an API that lets 'third parties' submit their own challenges. On top of that, we're also making it really easy to deploy your own MapRoulette server. If you're interested in any of that, just let me know. I will be hosting a session on MapRoulette at State Of The Map US this weekend, and Serge and are also planning to run a BoF session for a deeper dive into MapRoulette challenge making. If you don't make it to SOTM US, don't feel left out - there will likely also be MapRoulette sessions at SOTM EU in June!