What are the consequences of not caring about traffic jams?

There could be issues such as garbage trucks not being very efficient. Likewise any service that uses the roads will have difficulties. Fire trucks, police cars etc.

With that information in mind I am sure you can make the decision whether it is worth it to you, to remedy the situation or not.

Edit: Additionally it creates some noise pollution, which will reduce nearby land values and the happiness of people.

Traffic jams are important to take care of for several reasons.

• It creates noise pollution which makes people unhappy around the area.
• Services such as police, transportation, fire trucks etc. Can completely halt, for instance in the case of crematoriums dead bodies will pile up and can quickly create a plague that will kill your population (yikes)
• Industry needs well planned out road access for import and export. If businesses are not able to maintain profits they will move out. As your industry develops, it will require more traffic to operate.
• It affects overall happiness for the part of the population that travels the stretch.

All in all, neglecting it is a bad move, and is a big part of what Cities: Skylines is about. If you don't like it, you can use mods to remove the requirement :)

In addition to the other answers, I have experienced death as a consequence of this. Massive, city-wide, death. Since the trucks from the crematoriums and cemeteries couldn't get to the houses, especially when they became high density, more and more people died and more and more buildings were abandoned because of decreased land value.

The same can occur with other elements of your city, such as fire, police, etc. Neglecting this is truly a bad move.

You'll get a sea of warning indicators saying:

• Garbage is not being picked up
• No one is picking up corpses
• Cannot get raw materials
• No one is buying industry products
• Can't get goods to sell (retail)

If you don't resolve the problem, the indicators will go from green to red to "Abandoned" (gray box).

this is a mild case. To make it clearer, I picked electricity Info View. White buildings are either upgrading, or abandoned.

Most will fix themselves after 4 in-game weeks. But in residential, you better demolish them by hand, or you'll get Detroit, and a sea of warnings like this:

• property value is too low

So the whole city's "house of cards" can collapse.

What's going on?

Inside the game, imports, exports and deliveries are not abstracted. Right-click on any truck and you'll see it's a specific load, from a specific industry to a specific retailer, with a route (down to the lane) chosen at departure time.

You'd think when a building calls a garbage truck, hearse, police, fire etc. it would always come from the nearest unit. But actually there's some randomness to it*. So when it randomly picks a provider that requires a freeway drive to get to it, one of its vehicles is now stuck in traffic, and the building is not getting served and the truck is tied up. Soon, the provider has more and more vehicles stuck in the traffic jam.

This reduces the number of overall service vehicles available, sometimes dramatically. I've seen backups that (from the info views) are just stuffed with garbage trucks, fire trucks, ambulances, hearses, or whichever vehicle people are complaining about.

"So that's where they all went!"

Can you beat traffic jams by "island-ing"?

Yeah, kinda. You can create communities as "islands" and then connect them only by passenger public transit (and if they have any commercial or industry, freight rail/boat/air). Services will "stay on the island" obviously, and there won't be traffic jams on the island if roads are decent at all.

It will also strongly bias the island residents toward taking public transit on the mainland if it exists. But if not, they will take transit to the mainland, walk out of the depot, and summon their "pocket car" and drive off, adding to the mainland's traffic woes.

However, "islanding" can also expose certain really weird bugs in the game, as it hasn't been extensively play-tested for this type of play. Top of that list is service buildings no longer sending out vehicles, flipping between 0 and 1 patrol vehicles. This is caused a building somewhere asking for a service, yet no provider can path to it.

Also, freight boats and trains have finite capacity, and businesses on an island can overwhelm them - especially if they are regularly arriving with only 1-3 containers. (the limiting factor being docking time per vessel).

* My best guess is the randomness is to help the game handle islands. Consider an island connected only by ferry, freight harbor and subway. There is a cemetery on the other end of the island, but two on the mainland are closer. If it always picked the closest, it would never get service; so it picks one, fails to path, picks again, fails to path, repeat, repeat, repeat until it picks the cemetery on the island.