Link (highway)

The link tags are used to identify ramps or slip roads connecting other more standard highways to each other. Common link classifications are:

• highway=motorway_link
• highway=trunk_link
• highway=primary_link
• highway=secondary_link
• highway=tertiary_link

These of course correspond to the highway classes from motorway down to tertiary. But when a link connects two highways of different classification, which do you use? It is important to note that this is mainly a rendering problem. Applications don't usually need to know what type of link a link is, just that it is a link, so the admonition against tagging for the renderer does not apply here.

In any case do not split up the link into one part belonging to one road and one to the other with different classifications. This makes it more difficult to find out which roads a link is supposed to connect.

Link roads normally do not have names.

Contents 1 Interchanges 2 Simple at-grade intersections 3 More complicated surface junctions 4 Special considerations for motorways 5 Notes

Interchanges

At a typical interchange, some movements are grade-separated from others. This generally eliminates cross traffic from one of the highways (thereby making it possible for a motorway to pass through), but there are interchanges in which all highways have at-grade intersections.^[1]

Here the ramps can be considered to "belong" to the highway they split from and merge with. This is usually the higher classification of the intersecting highways, but in rare cases this may be reversed.^[2]

Simple at-grade intersections

The most common type of link is that which cuts the corner at an intersection, leaving a small "island" between it and the main crossing. There are also channelized turn roadways between the two carriageways of a divided highway.^[3] There is no consensus about whether these should be tagged with the higher or lower classification. Here, more than with any other type of link, the issue really becomes a question of which way you think will render better.

More complicated surface junctions

Sometimes, more complicated arrangements of links connect highways to each other, much like an interchange without bridges. Usually these eliminate direct left turns (see jughandle). Here too it probably makes more sense to consider the links as "belonging" to the more major highway.

Note that a regular surface road may be used for the same purpose. A preexisting street used to connect two major highways is not a link. Instead it should be tagged as a normal highway, probably equivalent to the lower classification of the ones it connects. This also applies where otherwise minor streets connect highways at an interchange.^[4]

Special considerations for motorways

In some countries (such as the United Kingdom, but not the United States), motorway has a legal implication: certain classes of vehicles (such as bicycles) and drivers (such as learners) cannot use motorways. The same restrictions apply to motorway_links. So the motorway_link tag should be used only on those connecting roads that have these restrictions.

Elsewhere, the question is not so clear. One might think that only those ramps that can only be accessed by using the motorway should be motorway_links. But then the central portions of certain collector/distributor roads are not motorway_links.^[5] Again it is a matter of which makes more sense: were it part of a through road, would it be a motorway? Always remember that a motorway and a motorway_link must follow certain standards (depending on the country), such as having no direct access to adjacent properties.

A motorway may have a short ramp of the type normally seen at a surface intersection, either because the motorway has a right-in/right-out junction, or because it ends just beyond at the road that these ramps connect to. Either way, these should be motorway_links where they solely provide motorway access.

Also note that highway=motorway_link implies oneway=yes (although the latter should probably be used anyway for clarity), and so a two-way motorway_link should be explicitly tagged oneway=no. This is not true for lower link classifications.

Notes