Cities: Skylines is easily my favorite city-builder of the past decade, but its expansions so far have been kind of lackluster. A big part of this is the fact that each expansion (so far) has had a pretty limited scope, meaning that I could really only recommend them if the expansion's particular theming was something that interested you.
While Mass Transit definitely has similarly tight theming, the effects of that theme are felt at a much broader level. Since Mass Transit seeks to specifically expand your transportation network (and fix some problems with creating transportation networks), and since every city of any size has a transportation network, this expansion has much more universal utility than any of the previous expansions.
Red light; green light
In fact, you'll likely start to see the impact of Mass Transit's new systems immediately upon loading up a city -- whether it's a new city or one of your established metropolises. If you're like me, then you'll immediately be thrilled to see that you can now name your streets. That's a cosmetic feature, but your budding young city will also soon encounter the new road and junction-management mechanics. You now have control over each and every intersection, and can assign STOP signs and traffic lights as you see fit.
As soon as I booted up the expansion, it informed me that it included a feature from my wishlist
Creating a main thoroughfare and want to make sure that traffic flows steadily through it? Assign it as a "priority road", which puts two-way stops on each road that intersects the thoroughfare, allowing traffic on the thoroughfare to move unobstructed.
Have a three-way (T) intersection? You can even assign only the "trunk" of the T to have a STOP sign, forcing traffic from that road to have to yield to traffic in the crossing road. Unfortunately, you can't add a median with a through lane.
You can force traffic to yield to major streets.
Even the tiniest of cities can benefit tremendously from this simple enhancement, and large metropolises can definitely see an improvement in traffic throughput with efficient use of priority roads. However, priority roads are really the only useful functionality of this feature. Since the game doesn't model car accidents (not even at an abstract level), there's kind of no point in creating four-way stops (as opposed to simply leaving the intersection without any stop signs at all).
This feature also usually entail some frustrating micro-management, as having to manually assign traffic lights and STOP signs can be tedious if you get stuck having to do it for every new intersection. There's also consistent issues with named roads not maintaining their names when I extend them, which forces me to have to manually extend the label onto the new road segment.
The much bigger benefit, however, is that managing traffic is made simpler by the addition of some new route overlays. Not only can you see how congested an individual road is, but you can also see which direction is most congested and also where all the traffic is coming from. This is another item from my wishlist. You can use this feature to see the sources of traffic driving on the selected road, and you can also use it on individual businesses and homes to see where the people at the home or business are coming from and going to. You can even click on an individual citizen or vehicle and see the route that it's currently following.
[LEFT] Every intersection caused congestion prior to the expansion. Since Mass Transit,
you can use "priority roads" [MIDDLE] to speed up traffic in major thoroughfares [RIGHT].
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