A modern high temperature combined-cycle power plant gets between 50% and 60% of the available chemical energy in the fuel. An electric motor is about 90% efficient in its typical operating regime.

The average internal combustion engine gets less than half that. High efficiency diesel gets close, but still falls short.

This means that even on dirty energy, a large scale power plant charging an electric vehicle is more effective at extracting energy from fossil fuels.

That's in the ideal case, on the highway. On top of that, an electric vehicle recharges its batteries when it brakes, and spends no energy when idling, which is important for city traffic, and (for buses) when stopping frequently at stops.

And unlike diesel, as we reduce the reliance on fossil fuels for power generation, the amount of pollution in the air reduces with electric vehicles, air quality increases for everyone, and quality of life increases.

It’s cleaner but still worse than electric. Here is an article with explained rational that shows that electric buses using current grid electricity are cleaner than diesel.