Hi,
when navigating from for example Ban Som Poi (West of Sisaket) to Kanthararom (East of Sisaket), OSM leads you through the city.
Even that there is a brand new bypass.
I guess that this is due to that ion the city many roads are tagged primary?!
In my opinion this should be changed due to avoid city traffic and better navigation by using the bypass.
What you think?
I would like to ask first before I do sth wrong.
Greets
Andy
Hi Andy,
Good of you to ask, and I believe the Thai OSM mappers are a little divided on this one…
I recently had a discussion with a mapper who decided the best way to make vehicles go around Nong Bua Lam Phu, was to down grade the 4 lane Primary Hwy 210 to tertiary, while upgrading the Rural route 3038 (the bypass), to Primary. I argued that changing road status to force navigation a certain way was not correct, and against our Wiki advice.
This also brings another issue into focus where it is my belief that the tagging/status of a road should follow its Government designation. Ie, 2 digit highways =trunk, 3 digit=primary, 4 digit=secondary, and 4-digit with a province prefix, (known as a Rural road) should = tertiary. This is documented in our page https://wiki.openstreetmap.org/wiki/WikiProject_Thailand#Highway_classification
Now I realise that in a few places, predominantly towards Bangkok and the South, we do have instances of roads that have been mapped according to the physical characteristics of the highway. For example, a 3 digit highway might be primary where it is 2 lane, but becomes trunk where there is a four lane dual carriageway section. It is my belief that this is not good mapping, but I tend to respect others work and until we agree unanimously, I leave as is.
One clear disadvantage is when the maps are viewed at certain zoom levels, roads can appear very broken, until you zoom in. I would welcome comment from other seasoned mappers on this argument.
So back to your dilemma … to avoid being routed through a city, firstly you can check to see if a “big wide road” in the city has been tagged as trunk or primary. If it is not part of the official Highway, and does not carry a route number, then reduce its status to something less.
Another key tool, is to add the maxspeed= tag, to the city sections …which in fairness, can be taken from road signs, but I always think that if that info is not visible, then you are able to tag with the Thai legal speed limit in built up areas. The Thai rules are very confusing but if you used 45 kmph, that applies to most cars & trucks, so would work for your needs, without being too pedantic.
In the UK, I see they do this, and just add source=NSL (National Speed limit).
Throw in any Traffic Lights you know about, and it just may help … but remember, Navigation is just a calculation, and one local guy I know kept ranting about poor routing in Chiang Mai, sending him down the small Soi’s etc, etc. One look at his Garmin confirmed it was set to “shortest distance”… my point… do whats right for the map, and not try to make it influence the GPS.
Cheers 
Hi Russ,
thanks for your answer and your suggestions.
I totally agree with this.
A couple of years ago, we decided to follow international standards and tag road according to their importance in the highway network.
This is often consistent with the numbering scheme, but there are many exceptions. E.g. road #4 is not a trunk for some long sections between Chumphon and Trang (but construction is ongoing). In contrast, #401, #403, #406 are trunks for most of their length - despite their 3 digits. And #4311 actually replaces #4 between Phangnga and Tap Phut. For a user of the map, the road number is secondary to its usability.
At Sisaketh, the way along road 226 thru the town is surely shorter (cooncerning distance) than on 294 around town. Without other parameters like speed limits, navigation devices will send you thru town consequently.
How does 294 look like on ground? In the maxar imagery, it is partially a dual carriage highway, partially not, but looks like construction. If it is a well built fast road round the town in its entire length, I’d prefer “trunk”.
Hell yeah…two veterans, 2 opinions.
294 is a 4 lane Hwy, well built and open since 6 month with the 4 lanes.
Going there means a longer distance but less time.
Primary !
Add expressway=yes or dual_carriage=yes. The routing engine you used may not take care of that tag, but I can do when I generate maps.
https://wiki.openstreetmap.org/wiki/Key:expressway
That will allow for a co-existence of the ref number mappers with those who try to get a useful map.
Quite often I wished that the farangs mapping in Thailand should look both at the map and ground truth in their home countries, and then learn from there.
I checked today, in Sisaket Hwy 226 through the city is not named Hwy 226 anymore.
This is shown in DRR as well.
I will classify the roads as secondary / tertiary.
Btw - just asked myself why there is a Wiki and things are mapped not according to it?! 
Hi,
Unfortunately OSM mapping is more of an art than an exact science, and we have all developed our individual styles as to what and how we map things. There is certainly no problem with adding the expressway or dual_carraige tags, as it adds information. I’m sure all roads that that Bernhard has mapped will have this. Conversely, I have never used it.
I encourage you read all the various Wiki’s on what the tags convey, and you will have to come to your own conclusions.
Our Thai Wiki does need clarification in some areas, but until we can reach a consensus, I think its not fair to allow one person to change it … having said that, the Wiki can only ever give guidance. To make it explicit, would just make it too large to digest.
However, I’m sure we all agree on one standard when mapping the larger roads, is that of the roads with “painted islands”…
So, if there is a physical separation between the carriageways (ditch/barrier/grass verge, etc) then please map as two separate one way roads running parallel. And try to get as many of the U-turns added in, as a simple way, tagged as a *_link.
However, if there is a painted separation island (hatched line area) then please map as a single carriageway, and by all means note the number of lanes.
Cheers.
Got it