[Talk-us] I 405 in southern California lanecheck complete

Paul Johnson baloo at ursamundi.org
Sat Mar 7 07:57:27 UTC 2020

Just completed a roughly two month long process of checking the entire
length of I 405 in both directions in lane-level detail.  This was inspired
from exceptionally bad lane guidance on what is the busiest freeway in
America and competes for busiest in the world on my last trip to Los
Angeles back in December.

This took a lot longer than editing ~73 centerline miles of freeway should
have, even given the complexity, largely because of a couple key factors:

Lane access, placement and turns are not particularly well represented in
key editors.  This leads to a lot of unintentionally introduced noise when
someone else, well intentioned, comes in and tries to edit behind you,
actually reducing detail and introducing inaccuracies that won't be easily
spotted without these important elements being visualized readily in the

Placement tags get to be even more important where a ramp joins or leaves
its parent, as this lets the navigation system (or, hey, even Teslas now)
where to expect the the painted gore to split a lane from the rest of the
road and where the real ramp starts.

Likewise, change:lanes seems to not appear in many people's editors and is
*extremely* important given miles-long restrictions on changing lanes (into
and out of HOV lanes in particular).

Some of these well intentioned edits were *very* large and were actually
easier and faster to revert and clean up with an explaination than try to
conflate.  This really highlights the importance of smaller changesets on a
cohesive theme in a limited area (something I could probably work on a bit
myself), particularly in extremely complex areas.

Right now, JOSM has a turn lane editor plugin, but no access editor.  A
*lot* of this had to be banged out manually.

Some editors make it really easy to break relations without being noticed
(particularly route and enforcement).

Anyrate, feel free to take a look.  I really hope editor support,
particularly for lanes and lane access, greatly improves because not
highlighting and making it easy to maintain the integrity of these elements
really is important to best give consumers anything resembling consistent
navigation where it's needed the most.
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