if the conclusion is parsed down to "reduction in CO2 emissions from highway traffic", then my answer is that i dont know. Overall, I doubt that EVs will reduce CO2 emissions over ICE vehicles. My doubt comes from the CO2 capture side. The advantage that EVs have with regard to CO2 emissions reduction comes from the centralization of electrical power generation. That centralization enables practical capture of CO2 if carbon-based fuels are used for generating the electrical power. I dont think wind and solar can entirely replace carbon-based fuels for electrical power generation unless nuclear gets a massive rejuvenation.
I think methane fueled ICE vehicles are likely to be worse than EVs when all things are considered. My brief experience NG vehicles is that they suck. The amount of money spent on repair bills alone makes any other kind of vehicle preferable and the fueling aspect is arguably worse than for EVs.
"CO2 emissions generated in mining the raw materials for the production of electric vehicle" is chasing the wrong rabbit. Mining of raw materials happens regardless of what material is used for producing and powering a vehicle. I suspect that the cost and energy differential between mining the iron, aluminum, etc that goes into manufacturing an ICE vehicle is similar to the mining and energy costs associated with producing an EV and its batteries over the life of the EV.
The important difference in energy costs is in the processing of the raw materials that go into making and transporting the fuels for ICE fuels versus manufacture of the batteries and charging of those batteries for an EV. The manufacturing of batteries is not nearly as tidy as the refining of oil - not to mention that a good chunk of the stuff in EV batteries comes from oil/NG. When a barrel of oil is refined to produce x gallons of gasoline there is energy stored in those gallons of gasoline that can be normalized against the energy spent to produce those gallons whereas when a battery pack for an EV is produced it is effectively devoid of any stored energy and it's not like there is zero CO2 generated in the manufacture of a battery. If you think comparing the gas tank to the battery is a more appropriate comparator, then the battery still loses.
It's probably fairer to compare the fuel and maintenance costs associated with EV over the lifespan of a battery versus the fuel and maintenance costs associated with an ICE vehicle over the same number of miles as for the EV battery. I suspect that the maintenance costs are where EVs have the biggest advantage over ICE vehicles. If CO2 reduction is truly a goal, then that is also an advantage but i don't believe that politicians and their constituencies are sincere on that front.
the phrase "methane from CO2-free energy sources" is more than a bit odd. The C in CH4 doesnt just magically transmute to an inert substance along with a release of usable energy.
As an aside: if you ever have a chance to see a solar panel manufacturing plant you might mistake it for a small oil refinery - except that it will probably have a large berm built around the entire facility rather than only around storage tanks (assuming there's an adjacent population). That's because some of the chemicals used in the manufacturing process are rather nasty and nobody wants another Bhopal. I suspect that manufacture of EV battery packs are similarly messy. This is the part that most lay people miss when discussing the 'cleanliness' of various fuel/power mediums.
