selective booking by traffic police

there is this place i walk past practically every sunday where i see many cars parked against double yellow lines. then, there is another place i go to on most evenings where i see a few cars and some heavy vehicles parked by a road with a continuous white line in the middle.

the sunday place is very close to the city, within the restricted zone. the evenings place is along a quiet stretch of road leading to the chestnut avenue waterworks. so far, i have yet to come across a single car booked for any parking offence at this sunday place but i have seen a few vehicles being booked for illegal parking at the evenings place.

is there some kind of discrimination? why booked vehicles parked along a stretch of road where they do not really cause any obstruction because there is hardly any traffic? the other place where the offenders go scot-free has through traffic even on a sunday and sometimes the parked vehicles create problem for longer vehicles trying to negotiate a turn.

is it for security reason that the traffic police strictly enforces the no parking rule at chestnut avenue? but, what security? the waterworks in more than a kilometre from the offending site. or is it considered a greater hazard for a car to be parked where there is a continuous white line on the road when compared to one parked against double yellow lines?

or is it because the drivers of these vehicles are not so educated and so they are not likely to challenge the rationale for the application of the rule whereas some of those cars parked against double yellow lines are driven by well-connected people?

another reason i can think of is that the traffic police has granted "special permission" for the vehicles to be parked along fort canning rise on sundays?

it seems to me that the officer who goes around booking the vehicles is taking the easy way out. as there is less likelihood for him to be asked to explain or to justify his course of actions, he target those who will not write to their chief to question the actions. to me, that act of issueing summons to this group seems a bit dastardly sneaky and unfair.