Electric cars are certainly more efficient than internal combustion engines which lose two thirds of the fuel energy as waste heat. But if your electricity is generated from fossil fuels, the same inefficiency is just relocated from your car to the power plant. The so-called "well to wheels" efficiency for fossil fuels is about the same for electric cars as ICEs.
As others have said, the difference is taxes. Car drivers are a captive audience for fuel taxes because up until recently there has been no alternative. This means, of course, that any rapid switchover to electric vehicles is going to have a sting in the tail that most people probably haven't thought of. The amount of motive energy used by just
light vehicles (cars, vans etc.) in industrialised nations is about equal to all the energy generated as electricity currently. We would have to double the amount of electricity output to power an electric car fleet.
This poses two problems. First, where is all the extra power to come from? The obvious answer is to burn the same fossil fuels to produce it. But:
- this does nothing to improve our dependence on the finite fossil fuel resource,
- it does nothing to improve emissions (although it could relocate pollution out of the cities which is of some benefit),
- we already struggle to cope with the 10% annual increase in demand for electricity for other uses -- switching over to fossil fuel plants to double the output again would probably take on the order of a hundred years even assuming fuel availability,
- when you do the sums, renewable resources cannot currently hack this problem, at least in our neck of the woods: there is not sufficient sunlight in the British Isles to power an electric car fleet on a seasonal basis, unless backed up by months of battery storage; likewise the current grid could not cope with vastly increased wind power; ergo, we need battery technology that doesn't currently exist and even then the numbers probably don't add up,
- and all of this only addresses light vehicles, not trucks or other heavy transport.
The second problem is how to replace the tax revenue from fossil fuels. The only possible answer to that is to tax the replacement electricity at similar levels, regardless of how it is generated. So the dirty little secret is that the current low fuel costs of electric motoring are actually paid for by taxation on ICE drivers. In the event of a rapid switchover that benefit would, perforce, evaporate.
One other possibility worth considering is that the number of vehicles of all types will go down dramatically. This is based on the notion that driverless cars will be summonable to your door at the press of a button on your phone, so you won't need to own one yourself. Needless to say, it will then become necessary to tax each journey to the hilt, to replace revenues lost elsewhere.
In short: there's no such thing as a free lunch.