[pierreh]

More about inter-city traffic today, and especially about pass-thru traffic.

I already documented in this CJ the use of simple pass-thru subway lines. In the mean time I have implemented more of those. Here is a typical example, in Polsay: the subway line links Arcens and Salveille, with no station in Polsay:



In that case, the work of the traffic simulator is quite simple: what it finds arriving at one extremity of the subway tunnel, it has to move to the other extremity - what comes in, must go out, in both directions.

The story becomes much more interesting with highways, when there are ramps in the city in the middle, where cars, buses and trucks can enter and exit the highway. The traffic simulator should have a lot more choices with traffic incoming from an inter-city link.

A RHW-8S highway links Salveille and Polsay. In the morning, the traffic is very predominantly from Salveille to Polsay:



Summing up the numbers given by the 2 queries we obtain: 20'509 cars, 1683 'buses' (= Sims traveling on buses) and 5435 trucks. The highway is quite well used.

Looking on the Polsay side of the highway inter-city link, we see:



Measurements give 20'659 cars, 1516 'buses' and 10 trucks (actually, at the exact city limit the number of trucks is likely 0, and the 10 trucks are fed to the highway by the industries bordering the highway; at any rate, there is no such thing as inter-city truck traffic). The numbers for cars and buses are reasonably close to those measured in Salveille.

Now, Sims coming from Salveille in cars and buses are looking for jobs in Polsay, and there are ramps allowing to exit the highway into the city. Do they find them? Apparently only a minority of those Sims do find work in Polsay, the majority of them stay on the highway that goes thru Polsay and links to Arcens. Here are the stats taken on the highway near the connection to Arcens; it has become a RHW-6S:



Of the 18'946 Sims in cars going to Arcens, there is quite likely a small number that resides in Polsay, but the majority of those Sims come from Salveille. And the enlarged traffic map for Polsay shows that the highway is busy (red) all the way thru that city:



Now the plot thickens: one would expect that those Sims who couldn't find jobs in Polsay, would then find jobs in the next city, Arcens. This is probably true for a minority of them, but the majority drives thru Arcens to the next city, Deramey! Again, there are ramps in Arcens allowing exit from and entry into the highway. On the Arcens side of the highway link we see:



There are 18'849 cars - very close to what the query on the Polsay side shows (we ignore the 'buses', because of the small numbers, athough the reasoning probably also apply to those). At the inter-city link to Deramey we have:

 

We see 18'651 cars - again, very close to the previous measurement. And the traffic map for Arcens shows clearly that the highway (circling a part of the downtown area) is busy from end to end:



What happens in the next city, Deramey? Do the Sims finally find jobs there, or do they, poor souls, have to forge on the next, and final city, Cherenne? This will be examined in a later post.

But already, this leads to wondering about the traffic simulator's 'tactics': it would seem that, given the choice between finding jobs for Sims in a city that has a highway passing thru it, and letting the Sims driving their cars remain on the highway to the next city, the simulator favors having most of the Sims stay in their cars and drive thru. The destination finder part of the simulator considers the next city to be closer that any commercial or industrial location in the city - which is probably true in most cases. The simulator works according to the rules documented; the actual effects on the intra- and inter-city traffic are rather interesting.