It makes that dealing with as few things as possible at a time is essential to safety. Humans are remarkably incapable of multi tasking that well. Combine that with a heavy machine going at high speed and you have a recipe for problems.
This also applies to someone on a bicycle. It's difficult to focus on everything you need to do, and do things like look over your shoulder, judging the speed of cars, thinking about what you need to do and planning ahead, while keeping the bicycle straight at speed, and balancing as you do. And given that children also ride bicycles, and more elderly people do it, it needs to be something with a much wider range of people accepted. And you are inevitably going to have the guy on their cell phone, talking on their cell phone, drunk, high, etc, riding their bicycle, and while they're dumb ideas, at least a car shouldn't be running them over.
So dealing with as few things as possible should be implemented. A single lane road has some benefits that multi lane roads don't. You can't have cars shunting you from the side on a single lane road on an ordinary stretch of road. Just one of the benefits. A cycle path should be added to all high speed high volume roads, so that you have a place to ride, a place where everyone knows who will be where, no more questions about whether a cyclist is on the sidewalk or roadway. It also makes that you can break up intersections into a series of steps. You can bend out a cycle path between 5 and 7 metres, sometimes 10 metres or more, from an intersection, letting a car, or someone else for that matter, turn from a roadway at a slow pace, face the cycle path 90 degrees, and not in the way of traffic from the main road, making drivers feel OK about waiting, able to look both ways for cyclists and pedestrians, and proceed. The middle of the road can have a waiting area in the middle. Especially useful in places like near the Best Buy in South Edmonton Common, where I often have hard times turning left out of because of the constant flow, but I don't want more traffic lights. This also lets cyclists break up crossings in a similar way. Pedestrians again also can do this. They already do at modern roundabouts.
Having separate turn lanes in each direction at a traffic light allows each lane to be controlled separately, maximizing the output of the intersection, for example when a left turn arrow is being used for a NB to WB turn, EB to SB can also get a right turn, as there are no conflicts. Same with bicycles and pedestrians. If they have their own signal, it can be controlled separately, and lets them deal with as few things as possible at a time. It removes ambiguity about who is controlled by which signal. And the separate turn lanes at a traffic light removes a lot of pressure to make the turn in the quickest possible way, with less regard for oncoming traffic, cyclists and pedestrians.
Roundabouts, with single lanes, cyclists yielding and median refuges, and a non annular cycle path design, lets people deal with as few things as possible at a time. You know that the traffic will come from one direction only at a time, and in only a single lane. It's always look left, then right, regardless of which direction. The median refuges and the space between the cycle path going straight on and bypassing the roundabout and the turning area lets you break up the crossing and have good sightlines. The self enforcing speeds of roundabouts keeps it low, 25-30 km/h. You can see very well.
The local access roads being the only roads you use to access homes and businesses has the advantage that what you are doing is at a lower speed, so you have more time to react. A lot more time to react. In all your thinking about the cyclist in front of you, the little kids on the sidewalk, opening your garage door, and pulling to the right to deal with the tight corner radii, means that you have as little to do at high speed as possible, because you don't have the high speed. And the near lack of moving cars, and bicycles are less frequent because they are on their main routes, on completely separate bike paths usually, makes that you have much less traffic to deal with, and much less pressure on you to do anything in a hurry.
Freeway interchanges are designed so you have as few things to do at once as much as possible. You turn left or right onto the ramp, then you accelerate up to highway speeds, and then you have plenty of space to merge. Why not have the same logic on our ordinary roads.
This strongly relates to Sustainable Safety in that you have perception of your tasks to do and how you are going to complete them, also formulated in the words: Road user awareness. It's a critical element to making roads safe. Humans unfortunately don't have the power to extinguish our fallibility, so the next best thing is to make our roads understand this, and deal with the problem directly, rather than huge campaigns to warn people of various dangers. If things feel natural, they do it. 130-140 is a natural speed of traffic on the highways where it is clear, mostly flat, fairly straight and wide with grade separation and a divide between the two directions. So designing for that speed in mind is usually the best thing to do. A speed bump on a freeway is not something people go over. Designing roads so that a 50 km/h speed on a distributor road away from homes with separate bike paths feels natural and so will in fact do it is the best medicine. It removes the need to determine the best speed, because you feel torn between the speed of traffic and the speed limit, like I often am on rural 110 km/h zones.