Talk:Relations/Proposed/Overtaking

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Why relations?

This looks so much easier as a tag on the highway parts itself... You'll create a huge relation mess if you have multiple overtake restrictions on different parts of the same road. --Eimai 13:56, 13 June 2008 (UTC)

Simple overtake restrictions, as marked on the ground, can likely be part of the highway, but the suitability is dependent on different parts of possibly different consecutive ways - and directions. Splitting a way just for adding something like easyovertaking=forward/backward/both/1/-1 doesn't appeal to me... Dedicated overtaking lanes wouldn't need this if they're really and correctly tagged as lanes=3 but would need a direction defining tag.
I'm mostly thinking of countryside roads where good opportunities aren't that dense and where easy overtaking places are far less common than places where overtaking is allowed. In urban areas, where speed limits are lower, the line of sight is more often always sufficient than not. I'll modify the proposal to a bit to state that these would be for highways where overtaking is otherwise not-everywhere-so-easy. Alv 14:32, 13 June 2008 (UTC)
But still, if you want this for say a 10km long mountainous and windy road, you'd need dozens of these relations on the same road. So that becomes quite unreadable easily with no easy indication about the information contained in it (or you'd need to change the editors so they can do this kind of thing more user friendly, but I don't see that happening soon... raw relation handling for this will really be ugly, believe me :-) ), so you could split the road to make it more readable but then you could better do it as tags on the highways itself.
Country differences here, again. My thougts were about a 100 km/h road and a trailer going 87 that one would want to pass: 25 meters + margin 2 * 15 meters to overtake and speed difference of 27.8 m/s - 24.2 m/s = 3.6 m/s, thus it takes 15 seconds to overtake and the overtaker drives 425 meters on the wrong direction lane - add a safety margin of 4 seconds and consider that the opposing traffic might also travel 425 meters during the overtake. Then by definition there even couldn't be 10 "good overtaking places" on that 10 km section. Even passing a passenger car at those speeds would require a line of sight of 760 meters. My point being: Even if there were those nine good places on a 10 km way, they wouldn't be rare and wouldn't require tagging at all - or could be a some common tag for whole way passingplaces=many?
Some countries might (still) allow exceeding the speed limit temporarily while overtaking, which makes overtaking easier. Alv 11:07, 17 July 2008 (UTC)

Alv 16:16, 13 June 2008 (UTC)

I see the whole relation idea like this: cut up the road as many as needed (for speed, overtaking information, number of lanes etc), the information that belongs to the whole road (the name, a reference number) can be put in a relation then. --Eimai 15:21, 13 June 2008 (UTC)
My understanding is emphasizing more on the roles each node or way has in the relation and that relations are for the "virtual" entities. But well see what or any comments others give and this is still just a draft. Alv 16:11, 13 June 2008 (UTC)

Renaming to line-of-sight

Both the maximum (safe) speed and overtaking are dependent on posted restrictions and the length of the line of sight. Tagging both distinctly makes it harder to use the data for overtake planning but nothing a computer couldn't handle.

Use cases

Best case should be a known overtaking spot, where the overtaking driver keeps a safe distance otherwise but accelerates just before the start of the good overtaking area. Driver then has the options of safely aborting or starting the overtake just when the adequately long line of sight starts.

Reasons for official overtaking restrictions include hills and turns reducing the line of sight and crossing roads.

Fast roads

  • Speed limit of 80 km/h or over
  • Mostly one lane per direction, but
  • Can have dedicated overtaking sections with three lanes
    • Without a dividing fence and without a restriction for the opposing direction traffic to use, too, when available
      (Some years ago in Finland all of these were converted to the next case. How's it in other countries?)
    • Without a dividing fence but overtaking forbidden for the one lane direction
    • With a dividing fence - will be drawn as separate ways
  • Lorries and others driving at or below 80 are common
  • Required free length for overtaking likely at least 760 meters
  • Overtaking restrictions (painted and signposted) can be very common, especially where good overtaking places are seldomly encountered.
  • To see what's ahead the driver wanting to overtake must keep an adequate distance before accelerating to overtake
  • Drivers should be aware of the possibility of "minivalleys", i.e. spots where the road elevation drops for some stretch considerably and enough to possibly hide an oncoming passenger car, but then rises again to appear from a greater distance as a free straight. Such traps are likely being removed but some still exist.

Narrow but reasonably straight and fast roads

  • Speed limit of 60 or over (up to 100)
  • Likely relatively low traffic density
  • Just enough space for a bus and a passenger car to pass each other, passing places needed when two busses meet. Overtaking a passenger car is thus possible, a truck a challenge.
  • Likely many good straight sections
  • Relatively flat but might have hills blocking the line of sight required for overtaking.
  • Still overtaking places are either common or require a considerable length to be not too common.

Winding mountain roads

  • Speed limit irrelevant, tight turns are more restricting
  • Mostly one lane per direction, can have overtaking lanes going uphill.
  • Speeds preferred by drivers vary considerably, some going 40 and others 80
  • When driving at 80, overtaking someone going 40 requires a minimum of 200 meters free oncoming lane. That is, if one moves to the oncoming traffic lane two seconds before ramming to the back end of the slower car or decides to abort at that point, and oncoming traffic can also drive at 80.
  • When starting the overtake and going 40 behind the car being overtaken with two second safety gap, speedy acceleration (for a normal car) yeilds an about 160 meter required length for the line of sight. If the safety gap is ditched, required length drops to a minimum of 130 meters line of sight. This is assuming the car being overtaken does not accelerate.
  • Minivalleys are unlikely when the roads is constantly going up or down.
  • Overtaking restrictions are short/common/everywhere?

Jungle tracks

  • If width is sufficient for overtaking, likely the lines of sight are long enough about anywhere for the speeds used. (Not that I'd have ever been anywhere near one)

Sketches of alternatives without relations

Just to make it clear (to me also) that using tags only might be more cumbersome, I'll eventually sketch ideas on how to tag this without relations and how that would make it more difficult. Alv 20:22, 13 June 2008 (UTC)

1: splitting ways

Having entered some good overtaking places with the following system I think it's the way to go for most cases.

Split way whenever a reasonable passing place starts for either direction. Reasonable equals at least 10 seconds line of sight at approximately speed limit speed, i.e. enough to pass a 5 meter car going 20 under the limit with prudent marginals. For any position where overtake restriction for either direction (legal or sight, i.e. visibility less than 4*2*m/s at speed limit) starts, split way.

Say, overtaking=no/forward/1/backward/-1/both for every section/way where overtaking is (not) allowed and easy_overtaking=both/forwad/backward/no for every way for which there is a line of sight from the far end (and all points in between) to the other end, consecutive ways also tagged with a compatible easy_overtaking=*.

A user could be given a notice of an approaching overtaking section, or of the length and the start of such section. A section tagged as easy_overtaking=* should be expected to end at the point where the driver would expect to be back in his own lane, whether or not it is the start of a no overtaking section. Meaning that starting an overtake would get "harder" the closer one gets to the end of such section.

To decide:

  • no_overtaking=*: both/forward/backward/1/-1, 1=forward=forbidden in the direction of the way (overtaking not known to be forbidden if not present)

Or

  • overtaking=*: no/backward/forward/both. default=yes, allowed (or unknown) in both directions. no=banned in both directions, backward=overtaking allowed in the direction opposite of the way direction, both=known to be allowed in both directions

Pro:

  1. easy to enter, if one overtaking straight happens to be presentable by just one way (for both directions)
  2. information for the way currently traveled (guaranteed length) available as soon as the way is loaded

Con:

  1. but for one direction the good passing section might continue on the next way.
    • With incomplete data means only missed chances.
  2. up to three ways for one good straight + two ways extending to either direction just because of the overtaking information
    • Not a real problem for longer roads through the uninhabited places.
      • Except could become, where they're in a E-road relation; some have 500+ members already
    • More of a rendering challenge to combine the ways for sufficient space for names and suppressing the frequency of rendered refs.
      • Needs to be tackled for ways split for other reasons, too, so not significant.
  3. reversing any way means broken data (I've see enough reversed oneways to claim this a challenge)
    • JOSM has support for direction sensitive tags and this could be included, if agreed upon
    • Not that frequent anymore
  4. Some countries have overtaking restrictions for some road users only, e.g. no overtaking in a hgv.
    • overtaking:hgv=* (or similar) ought to be sufficient model for all known variations
  5. not possible to tag the situation where line of sight to the end of overtaking section is available and necessary well before the driver gets sight of the first section - what's around the bend could be known to be empty because such a long portion was seen before some local block. Conveying that to the driver beforehand is likely impossible, though, so of little value (imagine a suitable mountain road).
  6. not possible to tag a situation where several sections of good visibility overlap in the same direction (a long straight with a small but deep enough valley in the middle, a valley that can "hide" an oncoming car). These can't be represented by tags alone.

2: tagging just nodes

Tag any start and end of overtake restriction no_overtake=both/1/forward/-1/backward. Restrictions alone are not everywhere enough to define good places to overtake, so: Tag any start of a longer line of sight with line_of_sight_start=both/1/forward/-1/backward and the corresponding ends with line_of_sight_end=both/1/forward/-1/backward. Really, don't try. I just had to experiment with such tagging (have now removed them) and keeping track of things becomes just too hard.

Con:

  1. One deleted node messes up things.
  2. Only logical when one, or two consecutive, ways in the same direction use each of the nodes
  3. Reversed way messes up things.
  4. Overlapping line of sight -stretches underdefined.
    • Starting a los twice might not be an error but no way to know does an end-of-los end all lines of sight in that direction
    • Too easily entered by mistake

3: extra ways

For any stretch, add an extra way between the start and end nodes and tag it, say, line_of_sight=both/1/-1. If the highway connecting these nodes (on another way) has no overtaking restrictions for either direction, add tag overtaking=both/1/-1 or overtaking=no.

Pro:

  1. Easy to enter
  2. Can use overtaking restrictions entered onto the ways themselves.

Con:

  1. Look like clutter in editors, but

Access restrictions

For the places where the overtaking rules are marked by traffic signs, it may be better to include this in the Access restrictions proposal. --Eimai 12:56, 17 July 2008 (UTC)

Some scenarios I commonly encounter.
  • Overtaking prohibited, except you can overtake lorries and other hgv/buses.
  • Overtaking prohibited, except you can overtake slow agricultural vehicles.
  • Overtaking prohibited for lorries/buses, between certain hours of the day and/or days of the week.
  • Overtaking prohibited for lorries/buses in general (country-wide, Belgium for instance), but certain stretches are signed with an exception, so there lorries *can* overtake, again always or at certain times of the day/week.
  • Overtaking prohibited during rain and other downpour (snow/hail), for certain weight classes of vehicle (again: Belgium, +7,5 ton), even on stretches where during dry weather they are allowed to overtake (an exception to the exception of the preceding rule, just to make things easier).

All these are indicated by signs, and some of them make for extremely tricky combinations of flags. --Ldp 15:08, 1 August 2008 (UTC)