Tuesday, March 17, 2015

[Cities: Skylines] Come On In! The Traffic's Fine! A Case Study in Pictures

Simulations are an interesting genre, because if the reviewer is bad at it and don't understand why they're bad at it, they're going to be frustrated and write something like, "the whole traffic mess is a disappointment." Granted, games in general have that issue, but simulations are all about how well you understand the system and can build within that understanding, so it's pretty paramount to an enjoyable experience.

Traffic in city builders is always a bit of a mixed blessing. Cities in real life live and die based on their traffic. If you can't get to where you need to go, you won't go. Looking at Seattle--where I live--if you want to get across Lake Washington to the Eastside with any sort of expediency, there's a couple of 2-3 chunks of the day that you should try to avoid. It literally inflates the commute 3 to 6 times what it could be, taking over 2 hours in some cases where it would take 20 minutes without traffic. King County is spending $4.47 Billion to try and fix the issue.

Traffic is difficult to get correct. Traffic engineers have university degrees to help them with these issues. They have decades of history to fall back on in terms of what works, and what doesn't, and computer simulations to help test out theories before implementing them. So to come into a city builder like Cities: Skylines without this background means you're playing at a disadvantage. But to me that's the fun: trying to figure out.

And it's impossible to ignore traffic. If your traffic is backed up, fire fighters, police, ambulances, hearses, buses, and cargo trucks can't perform their jobs effectively. So, traffic's an important, inescapable component of city builder simulations.

My first attempt at building a city ended early because I wanted to take the lessons I had learned (especially about traffic and building effective corridors) to a new city. The image above is the start of said new city. Two chunks of suburbia surrounding the wasteland of garbage dumps and industry. Not pretty, but it is effective. A clear hierarchy of roads exist: highways to get from borough to borough, avenues to get to the heart or ends of each section, and finally smaller roads to disseminate local traffic to their locations. It works extremely well. Despite my highways looking ugly as hell because I was still learning the tools, they're quite effective.

Speaking of tools, I find the elevated road building tool to be an excellent way to go about it. Their logic for connecting up paths is quite robust. I found it really easy to build off/on ramps and even just small bridges over train tracks. Just PgUp to go up a level, and PgDn to bring it back down to earth. You can build your ramps however you like, as long as there are places for the pillars to go.

Picturesque view of my forest industry bridges
Of course, just because you can build something doesn't mean you should. Space efficiency versus traffic efficiency is an incredibly interesting question. A good example of this is the Elevated Roundabout. Someone made a really nice looking highway intersection that is extremely space efficient for distributing traffic. However, because all traffic in all directions is sharing the same ramp, it's really bad when there's a lot of traffic.

Quite pretty, and extremely space efficient.
However, in practice if you have high traffic in both directions, it buckles and backs up pretty severely.
Some of the uglier intersections are massive, but extremely efficient at traffic distribution. Basically, it feels like a lot of traffic is a space vs. efficiency balance.

And it's not like you're limited to roads for traffic. Pedestrian paths in a city core are actually very handy. Pedestrians do use them, and it can reduce inner-city traffic immensely. The Grid Block is a fun little prefab for setting that up, and since the pathways are elevated, the pedestrian traffic is mostly separated from vehicle traffic.

The pathways do take up a fair bit of space.
But pedestrians do make use of them, quite a bit if your city has a compact layout.

Traffic Case Study (in Pictures)

When I started building my super dense city center, with handy-dandy pedestrian walkways, I knew since it was on its own I'd have to deal with a large amount of highway traffic, both incoming and outgoing. What I failed to do was understand just how much there would be, and when everything fell flat on its face because I didn't handle that traffic, there were dead bodies and fires everywhere. Literally.

The above is an image of the interchange to my dense city center. Horrendous. Traffic backed up to the highway, traffic backed up inside the core, too. Everything was concentrated in that one section. Sure, there was a back door if sims took the off-ramp on the wrong side of the highway and then follow the industrial roads back to the city, but not a lot of them opted to do so. Possibly a failing in the AI, but not insurmountable. Clearly that Elevated Roundabout just was not working. But maybe there was a way to distribute traffic a little bit better.

Watching the traffic, it became clear that the intersections at the on/off ramps were hurting flow. I'd watch traffic start, then stop, then start. But what if I could make the flow less jittery? By removing these intersections and turning the streets leading to and from the on/off ramps to one-way, I alleviated a fair amount of traffic. The line-up to get into the city was less strained, but I did end up moving a lot of traffic to the central core. I needed to get some traffic away from that intersection entirely. We needed another intersection.

So I built an on/off ramp further up stream, but not in all directions. Only very specific flows. This had the benefit of relieving pressure on the roundabout. Indeed, it's practically pristine, but still in use. But despite using the same one-way street pattern at the ramps, we still had an immense amount of traffic on the two-way street running parallel. Folks were using that two-way street to get to the core and the exit ramp, so rather than make it two-way, I made it and further streets surrounding the ramps one-way.

Traffic is still mildly snarled, but that reduced gridlock immensely, at the expense of my core intersections (again). I haven't taken this further, but I bet if I can use one-way streets to minimize or remove left-hand turns across traffic, I could reduce gridlock even more. Also, my off-ramp requires traffic to make a hard-right turn to get on to the highway, which slows down exiting traffic quite a bit. If I could make the off-ramp a merge lane where they can actually accelerate on to the highway, I could reduce traffic yet again.

Traffic is Fine

Yeah, there's a couple cases where the AI algorithms for traffic come up a bit short. A longcut nearby might not be taken as often as you'd expect given traffic conditions at the nearby exits. Basically, the AI is a bit too short-sighted as far as search patterns for alternate routes goes, but then again, perhaps that's not far off the reality of actual populace behaviour. I'm not quite sure. But overall, I've found traffic to be quite manageable with some planning and just... watching the traffic. Take a couple minutes, watch where your sims are going, and see if you can expedite their route.

Also, mass transit. Seriously. Buses and Metro are fantastic at reducing overall traffic, and if you build your routes for busy areas, you actually make money off fares. A lot of money. My income quintupled from $3k a week to $15k a week once I added a bunch of transit. Which helped make me more money to continue improving roads.

The game's been a blast so far, nothing revolutionary, but a solid entry in city building games and a fine replacement for the most recent Sim City game. #CitiesSkylines, #Traffic

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