Trunk Road Classification

I noticed on another thread a question about stop lights and routing. My problem is similar and involves routing choice by software. But my question is primary about road classification. And that also involves number of stoplights, intersections etc.
There is a section of road is classified as a trunk, but has about 5 stop lights in 2 miles as well as a number of crossroads and driveways. I did read the wiki and it the description is very general. It says "limited amount of intersections and driveways. Question is how many is too many for this classification. What is the accepted practice? I know from personal experience that it would be much, much faster to get routed over to an interstate that is only 2 miles away.
I did read on another thread that it is up to the routing software to take traffic signals into account, but do they also take roadway classification into account when they do their routing calculations? I am wondering whether reclassification of a 5 mile section from trunk to primary would make the software think differently in its routing choices. Or would I have to contact the vendor to find out. Do General Magic and other closed source companies communicate with the OSM community on this stuff?
Thanks for any opinions.

It would be helpful if you would post a link to the trunk road in question.

It’s best that you discuss with the previous mapper why they choose trunk for the classification of that particular road.
You can see the editors in the history of the way. It is not up to “strangers” to determine the classification, local people know best. Each country has slightly different rules for the trunk classification. In Belgium, everything with a particular road sign is a trunk, regardless of the length, and the number of traffic signals.

Some navigation programs do not discuss their workings with the community. Others, like OsmAnd are open source and you can study their behaviour and even tweak it with a simple file.

In the case of General Magic, you can report the problem and they might look into it. I have done that in the past for similar situations. If you post the location here and approx. start and stop point, I can contact them as well, (I’m a beta tester) and let them know about your particular problem.

Thanks for the advice. I can’t figure out how to post links or images. If there is a help page I can read, please point me to it. The section in question is a stretch of road in St. Louis County Missouri USA. Road is MO-141, and the stretch is from Manchester road to I-44. Different sections have been edited separately about a year ago. One of the mappers is apparently a person in Romania who works at TeleNav, so not local. The changeset number is Version #5 · Changeset #59642031, if that helps. I will contact her, and the others.
I have already contacted contact General Magic with the questions and sent them a screenshot of the map with the routes and the area in question drawn on the map. But if you have contacts there, perhaps you would know better how to get things done.
Thanks again

As an update to this, I did receive a reply from General Magic. They do NOT currently even use traffic lights in their routing calculations, but it is on their “to do” list. They would not say about road classification, but I’m still pumping them for info.

If you are on there are buttons on the right side. One should be called ‘share’ (or something similar). Create a link and paste it here.

Of course it depends on the program. Here is the code of some routers: … … es/car.lua … ar-eco.brf … outing.xml

It is also interesting if you want to know what keys are in use.
I only looked at OsmAnd. It seems roadclassification has a small impact. But there is no difference between trunk and primary. But differences might occur because of other factors. The biggest impact seems to have the estimated speed.

In principle, however, it should not be taken into account what the Router make of it. Important is the definition, and sometimes interpretation, of the OSM-Rules. As far as I can see the MO-141 south of I 44 doesnt match my understanding oh hw=trunk.

Thanks Robert for the help on posting the links. I’ll look for that.
Could not get those links you posted to work, however I am not a programmer, so I wojuldn’t understand them anyway.
Thanks also for your insight. I agree, when classification is done, the OSM rules should apply above ant routing consideration. However sometimes, as you say, there is a certain amount of “interpretation” that has to be done in cases where the rules are not specific enough. On some roads, the classification could go either way. And if, in the opinion of local people who know the roads, the applied classification might be causing problems with routing, then a re-classification might be appropriate IMO. And if routing programs take even a small consideration of classification into account, a re-classification of a small section of the road might be enough, added to the other calculations, to make it select a faster route. Just a matter of fine-tuning, I guess. That’s what’s great about OSM. The input of local people.

Yeah, me neither. Copy an paste is not that easy. Here again:

Just take a look at the one of the linked documents. It is not that difficult. Staying with OsmAnd it has an explanation starting at line 45. In general the router calculates the “costs” of the route or a segment. There might be multipliers (line 135) or some fix values (line 164) to influence the calculated costs. The least expensive way is chosen. The real values start at line 381.

Thanks again Robert! Yes they’re working now. I’ll look at those. I just started experimenting with OsmAnd and I like it a lot. Their routing is very good. Although I have noticed that their search function misses some tags. But they seem open to input also.

Regarding Magic Earth, I did get a second response from them and here it is:

"Thank you for the additional details and for resending us the screenshot.

The routing speeds in Magic Earth depend mainly on the “maxspeed” tag (at least for higher class roads, e.g. not residential), and on the number of intersections along the road. The classification of the road is not taken into consideration.
Our developers will revise the penalties coming from traffic lights in case C1031. Thank you for your patience while we are working on this…"

So since the various apps seem ignore road classification, I will not pursue this further with the previous editor because it wouldn’t make any difference.
Thanks to all

Lots of routing sites and apps do use road classification (i.e. the highway= tag value) to influence routing.