Perhaps First model the declining fuel cost for heavy trucks and light vehicles. For light vehicles 20% consume 50% of fossil fuel. For semi trucks the economics already are positive for some use cases.
So first predict when fossil fuel consumption declines by 50%. Then model the projected price of fossil fuel as consumption drops below 50%, gas stations close and refineries shift away from gas and diesel.
That is the base line.
Next how do we increase the pace of conversion? Maybe Education first, then incentives to end life of fossil fuel vehicles before their expected end of life.