Isn’t it a wonderful idea to generate electricity using the wind energy created by moving cars. In the year 2006 some students from Arizona University designed this wonderful wind turbine to harness power from highways. And Highway Wind Turbines are now a hot area for research.
As you can see from the picture they have specially designed weightless blades which will rotate the rotor from the wind generated by vehicles passing by. It is estimated that these windmills can generate 9,600kWh per year. Though it is hardly a substitute for huge power plants it has its own place in energy production.
An alternative design is to use vertical turbines in the middle of the highways. Watch the video below. This design sound more promising than the former one as it can capture more wind power.
These designs may have some practical limitations. But again a highway wind turbine design is a cool mechanical engineering project. This is something you can do and since this is something new (though it was designed 5 years ago you can further optimize it) it will give you more credit than a usual project. A study along with working model will do the job.