I keep hitting in the red every so often with my big educational city. The problem I've noticed is that as you want to expand and add more schools and universities the more of the other things you need to survive like commercial and industrial buildings to pay off for it, and then as your population booms for the new workers and students you need to expand resources for bus services, police forces, power supply, etc. It can get to a point where eventually your city will go bust if you get too big and with not enough space to cram in more.

This is what happened to me. I have 2 universities now and 2 primary schools maxed out, a college with 2 extensions, and a high school. I've managed to account for all students now so I have 5,500 students enrolled. I noticed that students who went to one university capped out its maximum capacity and ignored the other university, so I divided the extensions on them so that one is now a university of law and the other is a university of science and engineering (yes, I managed to get in 3 extensions! It took a great deal of messing around with repositioning parks and redesigning some road corners to allow for more small buildings to expand into flats and skyscrapers to milk more taxes.)

With the population boom it has resulted in half the criminals being jailed, half of patients being treated at the hospital, some buildings might get burned down but usually my fire force can get to them in time, and my garbage dump is only accounting for 2/3 of all the cities' garbage. I have a feeling that I may need to build up Norwich Hills fast in order to assist with the garbage collection, especially if I put a recycling center there. Unemployment is also quite high with almost 12k workers being jobless, and I'm only fulfilling half the freight orders with no more room for more trade depots since the 1 trade depot I have cannot get the freight out fast enough on its own. I decided to drop in another trade depot to handle the excess amount of freight which meant busting down 2 tower blocks, resulting in me going over 1k in debt. I had to increase residential taxes to 11% to manage, and the workers were not happy. I have no other option though, my city is packed out and unless I begin shutting down things like the busses there is no possible way I can afford to run the city at 10% taxes.

Another thing I also learned last night is that angles are a bad thing unless you're using intersections. This seems to be responsible for a lot of the traffic issues where cars stop and start at corners and do u-turns. Restricting entries into residential areas to 1 and creating dead ends that don't join with the main roads was also a wise decision to make to prevent a lot of stopping and starting and cars doing u-turns at the lights. I've had no more congestion since changing all corners on the main roads to tight curves. If anyone else is getting trouble with roads being badly congested I would advise them to do the same thing, change the corners on the wide main roads to tight curves and for the clustered areas where there's small shops and houses to cut off a single piece of road that would connect to it so that there's only 1 or 2 routes into it. Here's a couple of screenshots to show what I mean...

As you can see the main roads don't have corners. The tightly packed area inside has though, this is unavoidable as you restrict the amount of land you can put buildings in and as long as the traffic isn't dense in these areas then it doesn't matter too much. There is only one entrance into the residential area on the right at the bottom and this is based quite a way down the main road so that there's no immediate traffic pauses by the 4-way intersection. This is also important, if you have road entries too close to an intersection this will cause traffic to pile up. On the left side you can see that the road that could adjoin to the central lane isn't connected so that there is only that one entry at the bottom-right. There's little to no traffic taking up the intersections and this is well into what would be rush hour traffic.

Here's another screenshot with the roads selected...

It's a bit hard to see but all the roads are highlighted either green or grey, indicating that there is no traffic congestion.throughout the city. There's also no pileups on the highway. In the middle intersection the road is a bit yellow, this is about as bad as it gets and doesn't last long before it becomes green again. Here's a better shot of that intersection...

There you can clearly see the small pileup in the middle of the intersection, and you can also see more clearly at the bottom the road that doesn't quite meet the main road. For some reason my population has dropped despite more skyscrapers appearing around the map, but even when this bounces back up again the traffic is still just as smooth with very little to no congestion.