According to my mystery guest scholar from a mysterious LTA think tank… Our existing road tax formula was, uh, formulated by a crack team of LTA scholars like myself, using nothing more than our scholarly brains and a costly supercomputer. The calculation might be a bit complicated for the layman without a degree in mathematics, admittedly, but the best mathematical equations tend to be so. Anyway, the end user doesn’t need to do the math, because LTA will do it for him and send him a reminder letter when his road tax is expiring. The motorist just has to pay up on time.
Our existing computation of road tax has served us well over the years, with a tweak or two along the way to keep it a fair deal. Of course, like how a HDB five-room flat incurs higher service and conservancy charges than a smaller unit, a bigger-engined car has to be subject to disproportionately more road tax than a smaller-engined one.
As far as we’re concerned, every car is more or less the same size. Our mighty minds have even devised a technical term for this universal vehicle: PCU, short for Passenger Car Unit. Whether your ride is an A-Class or an S-Class (“Best Limo” at the 2014 ST-Torque Awards), we consider it one PCU. My official car is an E-Class, by the way.
If we reckon a road to have a rush-hour capacity of, say, 1000 PCUs, the individual size of the cars caught in the gridlock doesn’t matter, because it has already been factored into the equation. The only dynamic, which is a moot point anyway to us LTA scholars in our ivory towers far away from the traffic jam in question (five things to do when caught in gridlock), is the bumper-to-bumper distance.
Okay, end of discussion (click her for a counterargument), now for some real work. Today feels like a good day to play my favourite LTA game, “Mastermind: ERP Edition”. 
