Imagine you're in charge and have free reign, no limits: What would you change about roads, rules, infrastructure, cars, enforcement, etc.?
Well, my quick answer is that you have to change everyone's thinking about travel and who has a right to be on the road. You would also have to add some infrastructure.
My long answer follows. Don't worry, it isn't that long.
We need to make an environment where our children can conceive of riding their bikes everywhere and be safe while they do it. That implies changing infrastructure to some degree, large or small, depending on how you wanted to spend the wealth of your kingdom (and you would have to be a monarch to have free reign, with no limits). The infrastructure might be separated cycle tracks. And it might include new paths, but only if you want to use eminent domain to take land. I'm more of a benevolent dictator and would avoid that. We would have to consider parking. Most streets, even with bike lanes, leave little room for cyclists when cars are parked, at least if you want to avoid getting doored. This may mean eliminating parking on one side of streets so that the bike lanes could be widened without losing driving lanes - I drive more than I cycle so I'm trying to speak from two perspectives. Since we would have less parking, we would need, at least in this climate, better mass transit to get people very close to where they want to go. That would mean both rail and buses. Not everyone wants to ride in the winter so we have to consider that getting more people to ride might mean getting more people to ride in 3 seasons and leave room in our infrastructure for that fourth, colder and snowier season. You might be able to ride in subzero weather but I don't have the vehicle to get my boys to day care and school in extreme cold yet. (I realize this is my weakness - I saw a present, or former, member of the Somerville bicycle committee riding his son a couple of mornings ago in his box bike with a windscreen for his son, and it was very cold.)
So changing thinking would be the bigger problem and would return the most rewards in safer roads, for cyclists, young or old, and for drivers. School should include instruction on proper road use, both for the safety of the students and of other people when they start driving. It's the law in Massachusetts that cars must drive a safe distance from cyclists - the distance isn't defined but if you hit someone, or disrupt their riding (to the point of them swerving or falling) with your proximity, it must not have been safe. But this is not a well known fact. Nor is where a cyclist should ride. Last year I was cut off by a women, who I bet was drunk at the time (before noon), who then yelled at me to ride on the sidewalk, which is illegal where I was riding. I had my two children with me (one on a bike seat and one in a trailer) and didn't appreciate her cutting me off nor having my children hearing her yell invectives at me. But it goes both ways. Not a month after that, and a block away, I took a left, with the light, and was nearly cut off by a cyclist who similarly yelled invectives at me and came back at me, aggressively, until he saw I had a child with me. He acknowledged that I had the right of way but that he had three hours to get to Manchester, NH (so leave earlier if you choose to ride 45 miles). It goes both ways. We need to educate our drivers and our cyclists to pay attention to laws, at least in Massachusetts.
I'd like to change laws to something like those in the Netherlands, where the driver of the more massive vehicle is at fault, unless can be proven otherwise. I recall the very sad death of a man, a father and husband and younger than me, in Wellesley, who was struck by a truck and killed last year or the year before. The grand jury let the guy off because he said that he didn't see the cyclist. As a driver I see every cyclist, not because they are a cyclist like me and I'm aware of them, but because they are a human being like me. And I can't imagine that you could hit a cyclist unless you weren't paying attention. Maybe your truck, or car, is hard to drive. Then don't drive it. There are other people out there who deserve competent drivers on the road and not someone who can't handle the vehicle they are driving. And if they can't and cause harm, great or small, then they should be liable for it.
I would also change enforcement, so that a cyclist complaining about an aggressive driver would be taken seriously. Maybe all cyclists should have helmet cams, but that is expensive. (I have considered it but the cost is prohibitive, at least for a few years.) And police need to realize that cyclists have the right to be on the road, day or night - with proper lighting and reflectors for night riding. It's only risky because people aren't following the rules.