Introduction

This document provides an overview of how to tag oneway roads and helps editors understand the importance of this conditional restriction tag. Such tagging is necessary for both routing purposes and accurately representing roadways on OSM.

Prerequisites

You should know how to digitize road geometries, and you should know which tags are used to identify roadways in OSM.
You should understand how the road network functions within the country you are working in.
You should understand which side of the street the country drives on. This is commonly referred to as Left- and right-hand traffic.

Skill Instruction

The highway=* tag is the most basic tag used to identify a roadway or pathway in OSM. When mapping oneway roads, this is the only prerequisite tag needed.

Oneway Tag

The oneway tag is a type of access restriction tag used to describe roadways that are characterized by unidirectional traffic. When adding this conditional restriction to roadways/pathways, the tag oneway=* is most commonly used in one of two ways:

oneway=yes
oneway=no

Oneway=yes

A oneway=yes road allows traffic to flow in only one direction, usually indicated by signs or road markings. If only part of a larger road is oneway, split the way accordingly and apply the tag only to the affected segment.

Examples of oneway street signs:

Oneway=no

oneway=no is used to describe a roadway in which traffic flows in multiple directions. This tag confirms that a part of a given street is not a oneway street. Generally, this should not be added on every digitized road, but should only be used to avoid potential mapping errors in areas where oneway streets appear frequently.

Oneway=-1

In some cases, editors of the OSM community may have added oneway=-1 to roadways. This is done in rare circumstances where the direction of the way itself cannot be reversed. Since this value is only needed when the direction of oneway travel is in the opposite direction of how the way was drawn, mappers can avoid this situation by reversing the direction of the drawn way before applying the oneway tag. In order to fix roadways with this tag, the OSM way can be reversed to more accurately represent the oneway flow of traffic, then oneway=-1 can be replaced with oneway=yes.

Mapping in OSM

When adding oneway=yes to a road, first check the direction of the way in OSM. Each linear way has a defined direction, which should match the permitted direction of traffic on a oneway road. In the screenshot below, arrows show the way’s drawing direction; this direction determines how traffic will flow once the oneway tag is applied.

Reversing Ways

When adding oneway tags to ways that have been drawn in the opposite direction and do not match the real direction of traffic, the OSM way will need to be reversed.

To reverse a way in OSM:
In JOSM:	In Rapid/iD:
Select the way which you want to reverse direction and type `R`. JOSM will pull up this window when reversing a oneway. There are two ways to correctly reverse the direction. Uncheck the box under `Apply?` then select `Apply selected changes`. (If this box is checked, the tag `oneway=-1` will be added, reversing the way’s direction. Instead, it is preferred to reverse the direction of the way.) Select `Do not apply changes`. Always verify the direction and the oneway tag are both correct before moving on.	Select the way and type `V`.

Implied Oneway

Certain tags or tag combinations imply oneway traffic on a roadway. When mapping roadways that imply they are oneways, adding oneway=yes is entirely optional per OSM standards. Since the access restriction is implied, it is not technically necessary to add the oneway tag as there is no general consensus which tags imply oneway=yes. Since different routing programs may interpret these roadways differently, it is generally recommended to explicitly state if there are oneway restrictions.

For more information on implied restrictions see Key:oneway.

Roundabouts

The junction=roundabout tag is used to tag roundabouts. These are circular, self-intersecting junctions where traffic entering the roundabout yields to traffic within the roundabout. Since these junctions have oneway traffic, the tag oneway=yes is implied. For more information, see the Kaart: Road Geometry Guide/sandbox and the Kaart: Signs/sandbox pages.

Motorways

highway=motorway, also known as interstates in the United States, is the highest highway classification. These high-performance roadways have unidirectional traffic and therefore imply oneway=yes (among other implied tags). Despite this implication, it is recommended these ways always have the oneway=yes tag. In rare cases where motorways have bidirectional traffic along a single carriageway, oneway=no will need to be added for clarification. Below are examples of motorways with oneway=yes (top) and oneway=no (bottom) depicted in JOSM.

Conditional Restrictions

Oneway:bicycle

The oneway:bicycle=yes, oneway:bicycle=no or oneway:bicycle=-1 tags are used to define oneway restrictions for cyclists. For an explanation of this tag and its usage, refer to the Bicycle page.

	As rendered on OpenCycleMap

oneway:bicycle=yes usually matches the rest of the traffic's heading, but can also be found heading in the opposite direction.

oneway:bicycle=no is used on separate cycleways which allow heading both ways disregarding the normal traffic streets oneway status. These also can apply on bicycle lanes in some cases.

Oneway:conditional

The tag oneway:conditional=* is used to describe traffic restrictions that are contingent on certain days of the week, time of day, etc. For an explanation of this tag and its usage, refer to the Conditional restrictions page.

Using Context Clues

You will encounter oneways during many types of editing, and issues with them often appear in projects such as routing checks or missing roads. Oneways can be identified through various clues, including road signs and pavement markings. The best practice is to confirm them using all available sources. Below are some examples of how to do this.

Oneway clues to look for:

Direction of moving vehicles
Direction of parked vehicles
Physical signage in ground imagery
Roadway markings/painted signs

Vehicle Direction

In aerial/ground imagery, vehicles can be seen driving in exclusively one direction.

Cars are traveling westward in all drivable lanes.
Cars are traveling in a single direction on this highway on-ramp.
Parked cars are facing one direction in ground imagery.

Note: It is good practice to use multiple sources to verify a oneway.

Signs/Road Markings

Oneway signs and/or painted markings can be seen in available imagery.

Painted arrows are a simple yet effective way to determine oneway traffic in areas like parking lots.
This traffic light indicates turn restrictions here (no right turn). This sign, along with the oneway sign by the intersection, directs traffic in a single direction.

Kaart: Oneways Guide/sandbox

Contents

Introduction

Prerequisites

Skill Instruction