The FRT in my opinion should be formulated on emissions rather purely value (they use engine displacement for the licence fee).
The current license fee scales are biased, and not purely based on the effect on the road / pollution.
Biggest private car (engine >4,500cc): HK$11,329/year.
Biggest multi-ton goods vehicle (exceeding 5.5 tonnes): HK$4,694/year.
Double-decker bus (80 passengers): HK$4,025/year.
So long as Government remains deluded in thinking that FRT has significant effect on vehicle ownership, and muddles purchase disincentives in amongst pollution / road damage scales, it'll never make sense.
Using FRT to try to control vehicle growth rates simply doesn't work. Back in 2011, FRT was increased 15% and the affect on growth rate was near zero. In April this year the FRT waiver on EVs was capped, and the result is a 9% increase in new petrol vehicles put on the roads (comparing 2017Q2 vs 2016Q2).
If we want to incentivise clean vehicles, and correctly apportion road use, then obviously pollution/passenger combined with gross vehicle weight/kmdriven is the fairest approach.
If we want to control vehicle growth, then improving the alternatives (mass public transport, modern alternatives such as Uber, etc) and/or limiting the purchases (quota system), is the sensible approach.
If we want to control congestion, then the above coupled with ERP in congested areas, and park-n-ride to offer an alternative, is the obvious solution.
All the above can be revenue neutral. Just too many vested interests and opportunities for politically scoring points, to be possible.