A bit ago, the Seattle Times carried an article comparing living space to the space required by a car. Given 1) Singapore's expected population growth going forward, 2) that cars burn a lot of valuable real estate in the form of parking lots (at work and at home) and roads, and 3) a rising GDP / capita, it seems that the Certificates of Entitlement should face higher demand and less supply.
For fun, assume 4 out of 5 Singaporeans had a car; with 4.6M people, we'd have 3.7M cars; assume that everyone has VW Beetle or larger, 3.7M * 4 meters * 1.5 meters = 22M m2, with land available of 687 km2, we'd have 22/687 = 3.2% of SG allocated at any given point just to the ground under the cars at any given point. Let's add in the roads currently (to support 1 car for 4/5 people, we'd need more roads) with 3200 km paved, assuming 1 lane of width 3.25 meters, we have 10M m2 for roads, which means we'd have at least 4.6% of SG dedicated to cars and roads. Notice that the above numbers also imply that when ~50% of the cars are on the roads simultaneously, all the roads are completely full. So, it's easy to see how the amount of land allocated to cars could go north of 10%. So, in order to preserve access, SG needs to build roads vertically and/or build out alternative transport....
Singapore taxes several things almost punitively (cars, alcohol, cigarettes). While one can view this many different ways, I choose to think of it as Singapore gently reminding everyone that these things aren't good for us.