There's no free lunch!
Plainly put, anything you do is going to cost some environmental impact. Even if you're just going to walk (because making a bicycle also consumes resources and causes pollution) you're using up food (which cause quite huge amounts of pollution per Jule compared to other forms of transportation) and your exhalations are also adding CO2.
The point is to find the types of transport which allow for the least pollution and most effective use of resources. In such case the most promising seems to be hydrogen fuel-cells: Hydrogen being the most common substance in the universe, and fuel cells using a lot less resources to manufacture than a Li-Ion battery, lifespan on fuel cells are also a lot longer than the standard 5 year battery life, and only H2O is produced as by product (i.e. WATER).
But then nothing is said about the fact that nearly nowhere is hydrogen found in it's pure form. It's always combined with some other element (e.g. H2O). Thus to provide the H to add to your fuel-cell's tank it first has to be broken off the O by extremely high voltages ... again, we're back to using power plants. So even here we still have the fuss of coal, oil, nuclear, hydro, wind, solar, etc. And BTW, if you look worldwide (i.e. not just 1st world), coal is the overall most used power plant in existence - i.e. the most inefficient, most pollutant fuel possible would be the one used to "fill-up" your H on average.
And then there's other sources of H, e.g. through catalytic extraction from alcohol. But then where do you get the alcohol? Sugar-cane & fermentation? As if that doesn't have any impact on the environment! And what happens with the carbon residue after the H has been extracted? Landfill? Or are you going to use it in coal power stations?
And if you find an abundant easy to extract source of H. You're in effect adding more and more H2O - water vapor to the atmosphere. Uhmm ... anyone ever seen how quickly a man-made hot-house heats up when adding more water-vapor? Forget CO2! If you extract it from existing water, at least you're keeping a balance.
So if even petrol engines can be made to take in totality less energy and creating less pollution (used during extraction, manufacture, supply & use) than another form of energy - then that should be the preferred method between the 2. Please someone, could you find a few empirical studies to show the FULL IMPACT of comparable energy sources? This "testing with blinkers on" is causing more problems than it's solving. I can't seem to find any which even takes account of one source's total life-cycle (i.e. prospecting -> construction -> mining -> transportation -> conversion -> distribution -> usage -> by products), never mind comparing even 2 using these full-costs.