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In my area, there are a couple of bridges that are too narrow for two cars. Traffic can only go one way at the time. In most cases, these are low-traffic country roads, so there isn't any priority defined. How do I capture this in OSM?

asked 30 Mar '15, 11:29

TallArnie's gravatar image

accept rate: 0%

edited 30 Mar '15, 21:16

aseerel4c26's gravatar image

aseerel4c26 ♦

lanes=1 and/or an explicit width, see

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answered 30 Mar '15, 12:07

SimonPoole's gravatar image

SimonPoole ♦
accept rate: 18%


There is also the narrow key.

(30 Mar '15, 12:43) scai ♦

One reason to ask the question is to 'influence' the OSM route calculators. Most of them send me along this countryside route that has three of these narrow one-lane bridges, instead of directing me along the primary & trunk road. I don't think using the 'narrow' tag will have this impact, as it doesn't indicate the alternating one-way traffic. I have therefore changed them to 'lanes=1'.

(30 Mar '15, 13:33) TallArnie

background / half off-topic: @TallArnie: could you please mention a link to such a route which feels wrong for you? Maybe we could find another data problem there. Anyhow, it is important to get our data right – not to influence the current (known to you) routing algorithms/profiles. The profiles and algorithms change and due to OSM's open nature, there is a indefinite number of routing based on OSM data.

(30 Mar '15, 13:40) aseerel4c26 ♦

@aseerel4c26: I used and, and wanted to go from Rosslyn Chapel to Edinburgh Airport (= Jubilee Road). Two issues here:

  1. OSRM Takes you automatically to the wrong side of the airport (unless you're a plane spotter ;-)
  2. The most logical route for anyone would be to follow the city bypass (A720) and then the A8. Instead, a few miles before the airport it sends you along some really narrow country roads (it actually avoids the 3 narrow bridges I was talking about). Could this be because of the speed restrictions along the bypass / A8?
(30 Mar '15, 14:50) TallArnie

Part of the problem is that there are multiple Edinburgh Airport objects. The one you would actually want to use is the terminal This is a certain "weakness" of OSM in that we have a lot more data than you would normally have in a vehicle routing dataset and that the search function of at least OSRM is based on the full data, not just that which would be relevant for the intended purpose.

(30 Mar '15, 14:57) SimonPoole ♦

@TallArnie: do you mean this OSRM routing (update: new link, to the terminal)?

(30 Mar '15, 14:59) aseerel4c26 ♦

@Simon: Maybe Edinburgh Airport wasn't the best option, due to its ambiguity. Try Jubilee Road instead.

(30 Mar '15, 15:01) TallArnie

Here's one narrow bridge which is uncontrolled:
And here's the second one, controlled by traffic lights:
And here's the third one on the same road, also controlled by traffic lights:

(30 Mar '15, 15:01) TallArnie

@TallArnie, please use OSM links (not nasty Google ;-) ), possibly with a marker.

(30 Mar '15, 15:04) aseerel4c26 ♦

@aseerel4c26: Here's a better version of the route, as it turns out Edinburgh Airport is too ambiguous:

Re. those Google links: they're shortcuts to Street View images to illustrate the original posting about narrow bridges.

(30 Mar '15, 15:22) TallArnie

IMHO the weird routing is simply due to the maxspeed on the bypass being lower than on (some of) the residential/unclassified roads nearby. This is likely not easily correctable, obviously the routing weighting can be adjusted for the narrow bridges, however I expect that will just move the issues somewhere else.

(30 Mar '15, 15:30) SimonPoole ♦

@TallArnie, we are not allowed to use StreetView for your data contributions, so that is not really helpful.

(30 Mar '15, 20:48) aseerel4c26 ♦

@SimonPoole: thanks for looking at the reason! Yes, use of "narrow" as a kind of slow section ... or the routing profiles/engines need to be more adjusted to assume that a maxspeed of e.g. 50 on a residential road means an average speed (for route calculation) of 50*0.5 but 50*0.9 for trunks ... or an inclusion (if that is not done already) of lanes=1 / narrow into the calculation.

By the way: the mapquest routing is as it should(?!) be. graphhopper is "wrong" (by the way, if you set an "intermediate"/"via" on the big street, then you see that the route this way is just one (rounded) minute longer, so the decision for the small streets is a very close one.

(30 Mar '15, 21:09) aseerel4c26 ♦

Re. the routing, I agree that it is most likely based on the maxspeed attribute. The A720 and A8 are main arterial routes that have a speed limit of 50 and 40mph, whereas the little curvy country road is so quiet that it has got no speed restrictions, which means the legal limit of 60mph applies. This explains why the routing engine goes through this country road, even though no sane person would be able to drive this fast on (most parts of) this road.

(31 Mar '15, 13:50) TallArnie

@TallArnie There are tags for setting practical/advised speed limits but I'm not aware of any router using these tags at the moment.

(31 Mar '15, 14:19) scai ♦
showing 5 of 15 show 10 more comments

Regarding your original question, I don't think there's a way to make OSM understand that the oneway direction changes. New Zealand has many such one-lane bridges and when you arrive at one you either must wait until the bridge is clear of other vehicles or wait for a traffic_signal to turn green. I'm not an expert on routing issues but I would think that in either case, traffic crossing the bridge is merely slowed and would not need to be rerouted.

Use maxspeed=*, lanes=1, and place two traffic signals at either end of the bridge where appropriate.

permanent link

answered 31 Mar '15, 00:53

AlaskaDave's gravatar image

accept rate: 16%


If there's a traffic signal, that should be mapped. In theory routing engines can take that into account, and figure out that every traffic light adds (on average) a delay of X. This can make it realise a route without traffic signals is better.

(31 Mar '15, 11:38) rorym

For all bridges that only allow traffic in one direction at a time, I have set lanes=1. Where present, I have marked up the traffic lights at either side of the bridge. I have also set the maxspeed attribute where applicable. I have not used the 'narrow' tag.

(31 Mar '15, 13:44) TallArnie

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question asked: 30 Mar '15, 11:29

question was seen: 3,724 times

last updated: 31 Mar '15, 14:19

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum