# Threshold for dividing a road?

I’m still trying to work through the accepted customs for working with OpenStreetMap data. Right now I’m wondering what the rules of thumb are for choosing between using a single way or two ways for roads.

I’ve noticed that very small traffic islands (as either traffic calming or as short dividers next to a traffic light) tend to be ignored or noted just on specific nodes, and obviously roads with physical barriers between the two sides should be represented with two ways. But I’ve got a road where there’s a short distance between two traffic lights that has a decent-sized divider (maybe 3-4 meters wide, with grass and a couple of trees) in the middle. The road is here: http://www.openstreetmap.org/?lat=39.373247&lon=-76.740274&zoom=18&layers=B000FTF . It’s the secondary road, and the affected area is between the two traffic lights. Since the road recombines before any intersections, does it warrant separation?

Conversely, is it fair to assume that only physically divided roads should be represented by two ways? I’ve seen several primary-tagged roads that are physically undivided but are represented by separate ways in OSM. I assume a lot of that is because that’s how it came from TIGER (I’m in the US); should I combine those ways?

The way I see it, one purpose of showing a median is to show that you can’t just turn left anywhere. So if there are a bunch of driveways on a short divided section, I’d probably include the median. And yes, if there’s no median (which can rarely include a “paved median” that cannot be crossed), there should only be one way. If you can turn left anywhere, it’s definitely undivided.

Or indeed, right, if you are one of the 1/3 of the global population who drives on the left of the road!

Even if you are one of that third, you’d better drive on the right if you drive on the US roads asciiphil is working on.

Good point.

IMHO it comes down to which option will correctly route travelers through the intersection.

Either one will correctly route travelers (though if there are intermediate driveways one might need to use turn restrictions if a single carriageway is drawn), but routing isn’t our only use.

I guess I’ll leave it as one way for now. Logically, that’s how travel through there works (no driveways or other connections except at the traffic lights), so I’ll go the route of less complexity.

And I’ve recombined a few TIGER-separated ways where the actual roads weren’t divided.