It's (much) faster to bike somewhere when you have a tailwind.
This idea is similar to a low-speed version to Elon Musk's famous "Hyperloop" but predates its publication by a little over a year. Speeds of 800 mph appear to be practical for intercity transportation, but probably overkill within a city-sized area where congestion matters the most.
A network of proposed rights of way are dedicated for bicycle use only. Then a large box-structure in pre-cast sections make this path into a tubular configuration - one box for each direction.
At the terminus of each path, multi-megawatt wind generators power the system to generate a unidirectional wind of about 25 miles per hour. Cyclists then take advantage of this by cycling along the fluid flow such that they can travel to 25 mph or faster until they feel a headwind, in which case they will actually add energy back to the system.
The original NASA contest entry from 2012 can be viewed in  below.
Category of the action
Building efficiency: Physical Action
What actions do you propose?
First, a feasibility study of the system is to be conducted. Surveys may be conducted examining peoples' attitudes toward such a system of transportation. It is expected that localities suffering from the most congestion, such as Los Angeles, should garner a favorable opinion.
Second, a study of rights-of-way around the city should be conducted for determining which paths are suitable for cyclists. The box-tubes can be elevated above cityscapes, much like California-style freeway overpasses, which use a trapezoidal hollow cross-section.
Third, an authority (governmental or non-governmental) must be formed for financial accountability and transparency of the construction of such a system moving forward.
Fourth, a detailed study of the energy efficiency, and the environmental impact assessments, are to be conducted. This is the first 'expensive' phase of the project.
Fifth, land permissions and appropriations shall proceed. This would generally take the form of public land usage transfer agreements or purchases or compensation for privately owned land for places where columns for elevated wind tubes are to be placed. Seizure of land, a.k.a. eminent domain, shall be avoided or minimized.
Who will take these actions?
Business leaders, local governments, entrepreneurs, and engineers.
Where will these actions be taken?
How much will emissions be reduced or sequestered vs. business as usual levels?
A calculation indicates that the system efficiency is dependent on usage. However, Los Angeles experience has repeatedly shown that if something is built in a region of high demand, ridership usually exceeds the predicted amount.
Assuming that X% of car drivers uptake the system, the emissions from transportation CO2 will be reduced by Y tons in wholly avoiding the usage of a car. In addition, the congestion is reduced by a nonlinear fashion (i.e., for opposite reasons from the nucleation of traffic jams) which allows the efficiency of automobile traffic to increase by Z%.
What are other key benefits?
1. Reduced CO2.
2. Faster commute times.
3. Increased health and productivity.
What are the proposal’s costs?
The cost may be similar to a highway divided by 3, because of reduced size.
Elon Musk's Hyperloop (August 2013)
1. Chow, Brian. "Bicycle Wind Tube." Invent the Future Contest, NASA Tech Briefs (June 2012).http://contest.techbriefs.com/2012/entries/transportation/2884