Whatever’s left after the pols in Detroit get their cut and a few more hundred miles of bike paths get built.
Talking seriously about bike paths requires that we get very site specific. But at the level of broad generalities (to which we will promptly find exceptions when we get down into the weeds):
Bike paths are a legitimate part of the transportation budget in urban and high density suburban areas. I live on Capitol Hill in DC, the city's largest residential neighborhood with about 35,000 people, equivalent to a mid-sized suburban town. Fewer than half of us drive to work. There are many suburban areas where this could be replicated with adequate planning. It is very possible to get a significant percentage out of their cars. It's sensible to at least create the option. In other areas, bike paths belong to the parks and recreation budget. In either case, however, roads should not be built in such a way as to preclude alternative modes. I.e., roads should not become barriers. People should be able to walk around their own neighborhoods. People should not need to climb into their cars to safely cross the street. Rural roads should at least have a shoulder. And build that attractive off-road trail along the stream corridor sooner rather than later, after the area has densified, the residents are clamoring for more park space, and you are expensively retrofitting infrastructure that would have been cheap if done up front.
This means that the road plan should be designed from the beginning to coordinate with intermodal transit options, and that the road building budget should pay to mitigate adverse neighborhood impacts. And if we take care of pedestrians, we will take care of bicyclists almost by default. Since population is growing, this also needs to be done with an eye to how people will be living 30 or more years from now. Many low density suburbs will soon be high density suburbs or even new, highly urban places. They need to plan for this now. Build pedestrian and bike corridors today so you don't wake up to find a Tyson's Corner style traffic nightmare in the future. We are on track to double the American population every 40-50 years. Even if we closed the borders tomorrow, we'll be at 400 million by the time our kids are middle aged. Think about that now.
High traffic roads in urban and suburban areas should have sidewalks. Make the sidewalk wide enough for a bike to pass a pedestrian, and the biking problem is solved. Have a stoplight and safe crosswalk at pedestrian-friendly intervals (at least every two blocks). If that unduly slows traffic, provide pedestrian and biking overpasses. This is part of the roadbuilding budget, not the parks and recreation budget. It's a matter of building complete roads; commuters aren't entitled to destroy other people's neighborhoods.
In lower density suburban areas and in still-rural areas, roads should at least have wide shoulders. First and foremost, shoulders are there for traffic safety and traffic flow. (The guy ahead of you is making a left turn against traffic; the shoulder lets you get around him, as opposed to endless backups and one or two people getting through an intersection on a light. And people with minor fender benders can get off the road.) But bikes and pedestrians can piggyback on the shoulders, though a sidewalk or dedicated bike lane would be better. Shoulders are just common sense. The key here, however, is to protect the shoulders when, inevitably, the area starts to densify, traffic increases, and the car lobby demands another traffic lane. If a shoulder or sidewalk is taken for a traffic lane, that infrastructure must be replaced. This should be part of the upfront roadbuilding budget, not collateral damage for someone to try to patch up as an afterthought.
If the local situation does not allow for building a new shoulder (the houses are too close to the road and you don't want to take everyone's front yard), the non-motorized capacity must be replaced in other ways. This typically means paying attention to alternate routes. Arterial roads have always been unlovely nuisances due to noise, pollution and general ugliness; they are always neighborhood blights. But they become major transportation nightmares when the road grid forces everyone onto them, even for short neighborhood trips. Cul de sac style development is a big culprit here. The bicyclists, dog walkers, joggers, etc. can live with a major arterial road just fine if all they have to do is move over a block or two to a quiet residential street. But those residential streets need to connect so that you can move from one neighborhood to another without ridiculous detours. If the neighborhoods are absolutely determined to prevent cut through traffic, fine -- but at least build safe, accessible and well-marked neighborhood connector paths, closed to cars.
So many problems can be avoided if adequate planning is done up front. ALWAYS take a close look to make sure we aren't building roads that become barriers or that create chokepoints. Make sure that every bridge has a decent sidewalk connecting to walkable, bikeable routes on either side. Make sure that there are frequent crossing. Morning drive time radio in DC is a recurring litany of pedestrian-struck-by-car stories. (Sometimes a cyclist is struck, but usually it's a pedestrian.) This is almost always a matter of poor road design, the absence of sidewalks and a scarcity of safe crossings. All of this should be addressed in the roadbuilding budget. The commuter lobby is not entitled to smash other people's neighborhoods and expect residents to somehow pick up the pieces. Build the roads correctly from the start.