Hi to all my fellow members

Negotiating a roundabout would seem to have always had it's problems. The solution to a smooth transition through said obstacle is reasonably simple, providing only one vehicle at a time enters. Clearly this can be achieved with the use of TC's on both entrance and exit. The problem arises when there are multiple vehicles either passing onto the roundabout or travelling around the roundabout before exiting.

Having spent a number of hours trying to perfect a solution to this problem I have to admit to defeat. With my solution things seem to work for a period of time but then go completely off the rails, so to speak. My conclusion is to reason that variables and a counter system for each junction are the answer, but I have to say that my attempts, through limited knowledge, to implement these elements has also drawn a blank.

So my question to you all is, "Has anyone solved this issue" and if so would you be so kind as to point me in the right direction.

Cheers from a somewhat dizzy member

Pete

2 minutes ago, 220hotwheels said:

Hi to all my fellow members

Negotiating a roundabout would seem to have always had it's problems. The solution to a smooth transition through said obstacle is reasonably simple, providing only one vehicle at a time enters. Clearly this can be achieved with the use of TC's on both entrance and exit. The problem arises when there are multiple vehicles either passing onto the roundabout or travelling around the roundabout before exiting.

Having spent a number of hours trying to perfect a solution to this problem I have to admit to defeat. With my solution things seem to work for a period of time but then go completely off the rails, so to speak. My conclusion is to reason that variables and a counter system for each junction are the answer, but I have to say that my attempts, through limited knowledge, to implement these elements has also drawn a blank.

So my question to you all is, "Has anyone solved this issue" and if so would you be so kind as to point me in the right direction.

Cheers from a somewhat dizzy member

Pete

Apologies, I forgot to attach my attempt thus far.

Test roundabout control.mbp

Pete...

I imported this layout, and let it run for quite some time (enough to brew a pot of tea...), and found it to work almost perfectly. On two occasions, a pair of vehicles would try to occupy the same spot, and so linked together, but their different pathways made them separate again at the earliest opportunity. Whilst, technically, a Road Traffic Incident, and some dented bodywork, it resolved itself amicably and the World spun on. I didn't see any more chaos than that. Maybe if I left it running for a day or so, I don't know..? It looks to be about as robust a system as I've seen; I didn't try to delve into its workings to 'improve' it at all (I doubt that I could...).
What, precisely, went wrong for you..? How did the 'chaos' manifest itself..? I saw none; was I just lucky..?

Ich habe diese Anlage importiert und sie eine ganze Weile laufen lassen (genug, um mir eine Kanne Tee zu kochen...) und festgestellt, dass sie fast perfekt funktionierte. Zweimal versuchten zwei Fahrzeuge, denselben Platz zu belegen und kollidierten so, aber ihre unterschiedlichen Fahrwege führten dazu, dass sie sich bei nächster Gelegenheit wieder trennten. Technisch gesehen war das zwar ein Verkehrsunfall mit einigen Dellen, aber er löste sich von selbst und die Welt drehte sich weiter. Mehr Chaos habe ich nicht bemerkt. Vielleicht wäre es anders gewesen, wenn ich sie einen Tag oder so laufen gelassen hätte, ich weiß es nicht...? Es scheint eines der robustesten Systeme zu sein, die ich kenne; ich habe gar nicht erst versucht, es zu „verbessern“ (ich bezweifle, dass ich das könnte...).

Was genau ist bei dir schiefgelaufen? Wie hat sich das „Chaos“ geäußert? Ich habe nichts bemerkt; hatte ich einfach nur Glück?

Douglas

1 hour ago, Dad3353 said:

Pete...

I imported this layout, and let it run for quite some time (enough to brew a pot of tea...), and found it to work almost perfectly. On two occasions, a pair of vehicles would try to occupy the same spot, and so linked together, but their different pathways made them separate again at the earliest opportunity. Whilst, technically, a Road Traffic Incident, and some dented bodywork, it resolved itself amicably and the World spun on. I didn't see any more chaos than that. Maybe if I left it running for a day or so, I don't know..? It looks to be about as robust a system as I've seen; I didn't try to delve into its workings to 'improve' it at all (I doubt that I could...).
What, precisely, went wrong for you..? How did the 'chaos' manifest itself..? I saw none; was I just lucky..?

Ich habe diese Anlage importiert und sie eine ganze Weile laufen lassen (genug, um mir eine Kanne Tee zu kochen...) und festgestellt, dass sie fast perfekt funktionierte. Zweimal versuchten zwei Fahrzeuge, denselben Platz zu belegen und kollidierten so, aber ihre unterschiedlichen Fahrwege führten dazu, dass sie sich bei nächster Gelegenheit wieder trennten. Technisch gesehen war das zwar ein Verkehrsunfall mit einigen Dellen, aber er löste sich von selbst und die Welt drehte sich weiter. Mehr Chaos habe ich nicht bemerkt. Vielleicht wäre es anders gewesen, wenn ich sie einen Tag oder so laufen gelassen hätte, ich weiß es nicht...? Es scheint eines der robustesten Systeme zu sein, die ich kenne; ich habe gar nicht erst versucht, es zu „verbessern“ (ich bezweifle, dass ich das könnte...).

Was genau ist bei dir schiefgelaufen? Wie hat sich das „Chaos“ geäußert? Ich habe nichts bemerkt; hatte ich einfach nur Glück?

Douglas

Hi Douglas

It's great to see you back on the forum, your views have always been so beneficial and informative. What you have explained that went wrong for you is precisely the issue that I also have and which I am trying to resolve, at present not awfully successfully. Being mindful of the probability of both road rage and potential nasty insurance claims, I felt that my solution should not be finalised as is but still requires work in order to achieve 98% perfection, so still a way to go yet. Once the flow around the roundabout is satisfactory for cars and small vans then I will need to introduce the odd truck, larger van and bus, but for now that headache is well and truly on the back burner.

All the very best, take care

Pete

New File Posted already .... version2 already ... may run a bit better !!!!

I currently have been working on roundabouts.. Attached is a method I am currently using. It's based on the catalog "Country" round-a-bout because it was easier for me to work with. The cars are not all created equal, so I configure them during one of the entries to Accel=4 and Decel = 15. Not sure that is optimum. The cars still act a little different. Some fender benders still occur, but all in all it's usable for me.

There are two stops at each entry that seem to catch most of the cars that "jump the gun" so to speak.

The idea was to have minimul contacts and "code" to minimize resources since I have six roundabouts in use. Vehicles seem to be harder to use than trains. They attach themselves to each other a lot, and all of the vehicles seem to behave differently.

Maybe a little tweaking by someone, or better yet, someone coming up with a very good method, will produce an accident free routine.

Attached is my attempt.

Round _ A - Bout_2.mbp Round _ A - Bout.mbp

Bearbeitet Mittwoch um 01:20 Uhr2 Ta von hmclay
Ran it again ... found error ... then decided to change a routine(s) for more efficiency ...

On 1/14/2026 at 7:47 AM, hmclay said:

The idea was to have minimul contacts and "code" to minimize resources since I have six roundabouts in use. Vehicles seem to be harder to use than trains. They attach themselves to each other a lot, and all of the vehicles seem to behave differently.

Hi,

currently, I also work on a roundabout solution. Far from ready, but I tried a few general design concepts and found some basic rules for my design. Small roundabouts, like yours, leave little room for timing and need careful speed handling. This is where your delay of 0.5s can play a role.
Secondly, when you set a speed for a vehicle and another vehicle cuts across, acceleration can happen unless you set max-speed as well, and reset it at the exit.
The limiting factor I see, is the target allocation at the arrival on the stop contact. This is where timing becomes critical, because sometimes a vehicle is already close, but not yet recognised, and because your acceleration is low it can happen that they bump into each other.
I have chosen a different approach, but it becomes a bit more involved as far as coding is concerned. Your solution works quite well considering the small amount of code, however I still don't quite understand why you have chosen 2 contacts at the entry when you have "config" contacts further upstream.
My approach is different in the way, that the vehicles have targets early, for example from your config contacts. This allows a look ahead using targets if a vehicle is designated to cross the path of an oncoming vehicle. This way you can allow simultaneous entries for straight and right turning vehicles, they don't need to stop. Only when tracks cross you have to stop the vehicle until the path is clear. This allows more entries/exits (6 or 8) with generic code, but it is much harder to implement with the graphical EV.
The downside, and you mentioned multiple roundabouts, can be more complex target calculation, which is a problem with the MBS, because it is not async, it interrupts flow.
So lots of complex target calculations prevents a smooth animation. I hope Neo can do something about that.
regards
gmd

Hi to both @hmclay and @gmd

Very may thanks for your input into the problems regarding roundabouts. As you have both no doubt gathered my approach to most problems with MBS is to apply a somewhat long winded solution within my EV rather than utilising more sophisticated code. That is largely due to my extremely limited knowledge of such matters. Generally speaking this long winded approach usually works to a satisfactory degree but often requires the use of far more elements than might otherwise be necessary. For me the greatest pleasure of MBS is the construction of a layout, trying to achieve as close to reality as humanly possible, getting everything to work properly within said layout becomes secondary but nevertheless it needs to work to maintain the reality of the scene.

Clearly both of your approaches require a far greater knowledge of coding than mine but if you solve this issue then all I would request is perhaps a beginners crash course in making my EV somewhat more professional.

As the saying goes, watch this space, and once again many thanks for your thoughts and attempt at solving this issue.

Kind regards

Pete