As an aside, I suspect the heating elements in the windscreen wreak havoc with the in-car unit ('IU') installed in all Singapore-registered cars.
Congestion charges are deducted wirelessly off a cash card inserted in the IU - essentially a card reader - each time a car passes under a gantry (ugly stuff). The system is convenient to motorists in general if not aesthetically pleasing for the gantries erected all over the place - in town, expressways, etc. There are also numerous car parks that use the same wireless principle to provide ingress/egress.
I've had trouble getting in and out of some car parks although, thankfully, none with the congestion gantries, which would have entailed an administrative fee on top of the prevailing charge should the IU be unreadable/undetected.
Has any other Singapore XF owner 'enjoyed' this issue?
Ta!
Roy