I can think of several factors that would contribute to traffic in Geneva.
1. Cars in the middle of intersections when the light turns green. If you are inching along the road or even at a nice clip, you should look ahead at the traffic ahead and see if you'll be able to make it ALL THE WAY through the intersection if it turns red. I wait at the crosswalk until the car in front of me has left enough space for my car. And the far crosswalk doesn't count. Once they advance far enough and the light is still green, I advance. But, almost without fail, I see 3-5 cars follow me as the light turns yellow then red. They end up blocking the cross traffic, stopping on crosswalks, etc.
2. Pedestrians crossing (on crosswalks or not) when their light is red. When it's 12:00am and you can see a mile down the road in each direction and it's clear, yeah, sure, go ahead. But, if it's during the day, you can be sure that there will be traffic. I don't know how many times I've turned the corner along the lake right by Terrasse and Bains de Paquis, only to have to slow down because some people are crossing against the light. Yes, there are also many crosswalks where the pedestrian has priority, but I'm not talking about those.
3. People using a turn lane to "sneak" past others in the "go straight" lane and then cut in at the last minute. The place I see this most often is the route de Ferney going past Intercontinental and heading towards Airport/Ferney/Lausanne and going through a roundabout. After Grand Saconnex and the BP station, there is a two lane road: left lane heads for Ferney/Airport, right lane is a Bus/Taxi lane, but also for people going ON THE HIGHWAY towards Lausanne. At certain times of the day, the left lane is quite backed up, but the left lane is almost always empty. And without fail, car after car after car zoom past in the Bus/Taxi/Highway lane and then left-blink, left-blink, left-blink. "Oops." Bullshit.
I saw another example a few days ago coming back from Nyon during rush hour. I got onto the highway and almost immediately...brake lights. Stop and go for about 500-1000m. Then it moved a bit smoother, average around 60kmh or so, then again brake lights. But, this was as we approached a little rest stop on the side. From off ramp through the length of the rest stop and to the end of the on ramp, it was maybe 500m or so. And I lost track of the cars ("I'm more clever /important/special/immature than you are.") that sped through the rest stop. Blink, blink, blink, roll down the window, "can I get in, please? Thanks." Assholes, the lot of them.
4. People parking in the "bookends" section of parking spaces. In a row of parking spaces, there is almost always a triangular section on each end that is painted with lines (ie., "don't park here") which is used to allow enough space for the cars to wind through. This is usually on residential streets with parking alternating sides or with other "slow-down" measures, but can also be found on the lake roads, etc. People park here which interrupts the intended, natural flow of traffic.
5. The same can be said for people who park IN THE MIDDLE OF THE STREET in order to drop off the video rentals, library books, or - I saw this once - do their shopping in the local grocer. Park your damn car like the rest of us and WALK to the store.
And on and on and on. But, as the articles above discuss, cases have been found in the wild, where a simple tap of the brakes on a highway can cause a ripple effect felt for miles and miles and miles, the so-called Phantom Traffic phenomenon.
(Nope, I don't think about this much at all.)