Roads & Mass Transit

Roads are one of the most basic aspects of SimCity, but one of the most problematic and often misunderstood. This article covers how SimCity's traffic works and why this leads to problems, along with a few tips to help you get your city moving.

The following sections can be found in this article:

How Sims Move in SimCity

Over time the game will spawn Sims and give them a specific tasks to do which causes them to move around your city. These tasks are things like move into a suitable residence, go to a suitable school, shop or place of work, or for visitors, use a suitable culture or gambling attraction.

What does 'suitable' mean?

These Sims will be assigned a few basic characteristics, worker, shopper, student, their wealth level (low, medium or high) and their education level (educated or not educated). Some will be given additional characteristics like sickness, political protest, homeless, criminal, tourist etc, which prompts particular interactions with city services.

These characteristics determine the nature of their current task. Once they have a task they will move out from the residence or other point of origin (hotels, tourist entrance points like train stations or ferries, police station, hospital etc), to look for another location which fulfills their needs. They will travel towards the nearest available location that provides for their current need IF one is available. How they travel is determined partially by the distance they are travelling, and partially based on options which may be appropriate to their wealth level.

Sims will travel from their spawning point directly into the nearest building that can meet their current task. The further away that building is, the further they will travel.

How does this create problems within a city?

If there are no suitable locations for Sims to go to meet their needs then problems develop. If medium wealth shoppers cannot find any medium wealth shops to go to they will be unsatisfied and complain 'where are the shops?'. If Sims can't find a job they will become unemployed. The reverse is also true, industry that can't find appropriate workers will not function, shops that have no suitable shoppers will go out of business.

Heavy traffic can often be a symptom of poor zoning which typically results in a wide variety of problems such as unsold goods, unsatisfied shoppers, businesses with no workers, unemployment and general unhappiness.

Extra traffic is also generated when your city has some required buildings, but not enough for the number of Sims that need it because of the way Sims move around the city.

When a lot of Sims have to travel large distances to get to a suitable destination, they are spending much more time on the road than if they only have to travel a short distance. More Sims spending more time on the road = more traffic.

There might well be a suitable building available when a Sim sets out on their journey, but it can become unsuitable by the time they arrive, especially if that journey takes longer than it should due to traffic. For example the medium wealth shopper might find that the shop they are going to has run out of goods by the time they get there. The worker may find the factory is full by the time they arrive for work. The longer Sims have to travel to get to target places the more likely they will fail at their assigned task because there is only a limited time within the day cycle.

All Sims will walk rather than drive or use mass transit if a suitable desination building exists within 400 meters of their current location?

Essentially Sim wealth and education levels ideally need to match that of nearby commercial and industrial areas to avoid long journeys across the city to find shopping and employment elsewhere. Long journeys for many Sims results in heavy traffic and many failed journeys causing problems in your city.

If Sims looking for a suitable workplace are still travelling by the end of the work day cycle (6pm) they are considered unemployed. Unemployment in a city increases unhappiness, homelessness, crime, falling education levels and abandoned residential buildings

It is this mechanism that causes shopper and worker failure and unemployment even though your city appears on the surface to have enough shops or jobs or educated Sims to function.

Fixing Bad Traffic

Unfortunately I can't give you a magic 'cure all' for bad traffic because there isn't one, but here are some general observations which I've found which can help.

Avoid huge areas of a single zone type

Creating smaller zones mixed in together means Sims that are generated in residences don't have to communte far to shop and work. Keeping industrial zones small reduces worker shortages, freight shipping problems and traffic overall if there are local residential and commercial zones to support them.

Balance workers & shoppers against available shops and jobs

It is completely impossible to have a perfect balance of workers and jobs, and shoppers and goods BUT it is still a good thing to aim for! If there are not lots of unfilled jobs, or unemployment, or unsatisfied shoppers / unsold goods means most Sims have managed to get to a suitable 'need fulfilling' location before the day cycle ended.

Do not put any zoning along main routes

It is a bad idea to zone along central, heavy traffic routes. This will add local traffic and pedestrians crossing at busy intersections in the most jam-packed area of the city's road network. If there are no zoned buildings then there's no need for anyone to stop there. This will keep everyone driving through at a steady pace. If you really need to use these critical through-routes then try and restrict the buildings to the least clogged side!

Avoid intersections where possible

Whether they walk, drive or take buses, all Sims make poor pathfinding decisions at junctions. Often they will update their pathfinding route as they go around, which can result in endless loops like the one demonstrated in the video below.

It is impossible to avoid intersections altogether (I've tried this; it did not go well), but traffic flows better with 3-way intersections than 4.

Sims frequently make poor routing decisions, especially around intersections. This is demonstrated by this video "The Intersection Trap" - Xehlwan

Using curved sections instead of corners

Traffic comes to a stop at a corner, just as it does at an intersection; a corner is essentially a 2 way intersection. It interrupts the flow of the traffic so swapping out corners for a curved bend on very high traffic areas and major routes really helps to get things moving. It does take up a little bit of extra space, but it's well worth it for the reduction in gridlock.

Use Briges & Tunnels!

These were not available when I originally wrote this article!

These make an excellent fix for intersection related problems by having one road go over another. This allows both roads to flow faster as there will be no traffic lights and no waiting. Of course there is the downside that you're no longer joining one road to the other, which is fine for cutting across the city, but not good if you want to actually connect the two roads!

The solution to the latter problem is to use these bridge and tunnel options to bring traffic in on the correct 'side', so Sims don't have to cross the flow of traffic to join main road.

Avoid rushing to upgrade your roads, especially not as a 'quick fix' for bad traffic. Upgrading roads allows nearby zone density to increase which can easily cause zone imbalance and social and economic problems, including a sudden rise in traffic!

Use 'dedicated' areas of road network for specialization, universities and tourist attractions

If you have particular buildings which either generate a great deal of additional traffic, or which require smooth, traffic-free roads in order to function effectively, it is well worth exploring creating a parallel, or separate road network which interacts with the main city road network as little as possible. Such systems do inevitably wind up with choke points where they meet the general traffic, but if things like delivery vehicles can spend most of their time whistling up and down roads that don't go anywhere else other than to mines, factories and the storage depot, it will keep things moving much more effectively.

You can place the University pedestrian path anywhere in your city and Sims will use it for local short journeys

Add U-turn points

Quite often traffic jams occur because a lot of traffic has to travel all the way to the end of a long road in order to turn around at the end and come back along the road merely to get to somewhere on the other side. Adding very small pieces of low density dirt road can provide a turning place for such traffic to come off the main road. This doesn't work terribly well for areas which are at a standstill, but can be quite effective on roads which are merely 'busy'. The low density dirt road has no lights so exiting vehicles do not hold up traffic on the main road.

Put mass transit stops away from junctions and corners

Buses are more likely to cause queues of traffic behind them when they stop close to a corner, whether it is the corner just ahead or an intersection just behind them. Putting the stop in the middle of the road will give the best possible result.

Use the minimum number of school bus stops required for full enrollment

It is nice to share your un-used school places with other connected cities, but slow moving buses aren't always good for other traffic. Plus it's good not to add more vehicles to the useless regional highway!

Where possible it is better to focus school bus stops in 'quiet' residential suburbs and avoid using them in 'down town' areas. Keep an eye on buses going in and out of the high school, as they get stuck from time to time, causing a major jam (I sincerely hope this issue has been patched out since the game was released).

Share only high-value volunteer vehicles

Having a load of volunteered vehicles from neighbors can be a huge help when you're just starting out. But they can become real road cloggers later on and they add to regional highway jams. Once your cities are established consider making deals with neighbors to share only the high level vehicles, i.e. wellness, crime prevention, detective vans, hazmat fire trucks etc.

Service & Emergency Vehicles

Service and emergency vehicles all have their own unique and predictible behaviour which results in traffic problems.

Whenever you start a new city you can see how the pathfinding works by watching the moving vans. Garbage trucks and school buses will set out towards the nearest stop or building in a similar way. Frequently they will drive around in loops and double back in order to get to what the game has deemed the nearest target location, rather than going to the next building on the current street or what you or I would consider the most logical nearest stop. This causes their routes to take longer than absolutely necessary.

A car has become stuck turning out from a building onto the street. This has caused a traffic jam behind because another vehicle is waiting to turn in. They will remain there permanently without intervention

When a fire is generated in your city, ALL fire trucks which are not already engaged, will head towards that location by the most direct route and they will all continue to attempt to get there until it's gone out. Police patrols frequently have limited areas of influence because they tend to turn off onto the nearest 'next' street, even if they've been there recently.

Traffic Tips & Tricks

If things get really bad, here are some additional things you can try to get your city moving!

De-zone areas along busy routes

Getting rid of zoned buildings by de-zoning and bulldozing will remove sources of local traffic from alongside your major routes.

Delete the ends of roads that connect into your major city routes close to the highway

This is especially recommended if you have 4 way intersections, removing one or even both roads that lead in will stop that point in the road from being a queue. Granted it'll probably just move the choke point further into the city, but it will bring vehicles further in off the highway before they start getting stuck. The further in you can bring them, the more likely it is that some of them will actually reach their destination and stop being part of the traffic.

Down-grade connecting roads

Downgrading roads probably seems like the last thing you want to do, but I recommend trying it on areas that are directly connected to your main city entrance / exit routes (you may need to bulldoze zoned buildings in the area as they will probably not devolve on their own). Reducing the occupants of zoned buildings means those roads will generate fewer vehicles.

For more information:

Reduce your population!

It's one obvious option everyone seems to overlook. SimCity doesn't really support large city populations, even the most efficient road networks start to run into problems by the time the reported population gets to 200,000. If your city population is higher than this then you may want to consider taking the 'less is more' approach and cutting your city down to size. Having fewer Sims in your city should mean fewer vehicles on the road, more efficient specialisation, fewer economic problems.

Delete some road to break local jams

If there are sections of your road network which simply aren't moving then often you'll find it's because one or more vehicles has become stuck at the front, trying to turn out onto a main road or a junction. Since this doesn't always reset by itself the best way to deal with it is to delete the section of road. This will cause all the vehicles on it to reset to the nearest road segment whereby they will start moving towards an atlernate route. Typically it will take some time still if a lot of traffic has built up for everyone to get moving again, but at least now you've removed the cause, vehicles should be able to move as the traffic eases.

Only trade vehicles can use service roads

There may be occasions when you can utilize service roads to create areas within your road network which can only be used by trade vehicles. The advantage is that your specialization delivery vehicles can move freely within the service road area rather than getting caught up in the general traffic.

The photo below shows an example of this that I created in the city of Mesquite in Titan Gorge. My city has an extensive coal mining area and two oil fields. I have used the oil service road to create an entire road network around these, which joins a regular road bridge over the river on both sides. Because normal traffic can't use the service road either side, it also can't use the bridge in between. The result is that although traffic gets pretty bad on the main avenue down the side (very bottom of the photo), trucks delivering to my exporting trade depot near the city's exit, never get held up in traffic.

Mesquite: A combination of service roads and a regular road bridge provides a dedicated route for trade vehicles that other traffic can't use.

Obviously all roads have to connect somewhere along the line, but you can use service roads over an extensive area in this way to help keep your specialization vehicles moving smoothly (wouldn't it be nice, Maxis, if the service road was a standard road option we could use and define which types of vehicles could use it - anything from buses to garbage trucks, service vehicles or even just a car pool lane?

Total gridlock?

Unfortunately total gridlock where every street is crammed with stationary vehicles really does constitute a failure state for your city, it will lead to widespread social and financial problems and so often drastic action is required. When you've run out of roads to upgrade and you've tried to de-zone and re-zone to deal with the issues, but the whole thing has gotten out of hand there's really only one thing to do and that is to kick everyone out of your city and start over.