Tuesday, November 16, 2010

The Arithmetic of Number Coding and How It Fools Everybody

Number coding is a Mental Scam.  There is NEVER a Reduction in the Volume or Number of Vehicles potentially present on a given roadway--even with 100% Compliance with Number Coding.
Number coding should be abolished.  Mathematicians and statisticians ought to assure the public that nothing much would change except MMDA has to do things the hard way: by fairly enforcing traffic laws, removing obstructions and illegal vehicles from the roadways. MMDA should quit promoting official innumeracy with mental trickery involving percentages and absolute numbers!

[Updated]

TRAFFIC is a notorious part of living in a city like Metro Maligna, where it achieves monstrous proportions during holiday seasons in a maddening, spaghetti-like jumble of cars, buses, jeeps, motorcycles, pedestrians and pushcarts--crawling or dead-stopped for hours.

To alleviate this problem without really seeming to do any work, the Metro Manila Development Authority has been running a Vehicle Volume Reduction Program called Number Coding. 

Number coding claims to reduce the potential number of cars on the roadways by banning those with plate numbers ending in 1 or 2 on Mondays, 3 or 4 on Tuesdays, 5 or 6 on Wednesdays, 7 or 8 on Thursdays and 9 or 0 on Fridays between the hours 7-10am and 3-7pm.

By keeping one-fifth (or 20%) of all licensed vehicles off the roadways on appointed days of the week according to Number Coding we are reducing vehicle volume by 20% of the total number of vehicles that could potentially be on the roadways if we didn't.

It is a very convenient scheme for the MMDA to maintain because it presents the following commonly accepted notion: that the scheme reduces traffic congestion to acceptable levels by allowing only four out of five, or 80% of all the vehicles to travel on a roadway like EDSA on weekdays. Saturdays and Sundays are not covered.

But it is a mathematical and physical falsehood to  claim that the Number Coding Scheme is a "VOLUME" Reduction Program.  I show below that even with 100% Compliance by all drivers with the Number Coding Scheme, that the potential traffic volume on a given roadway on a given day is STEADILY INCREASING.

It has to do with the fact that in the Philippines the TOTAL number of cars is ever increasing.  At Year One, say,  we might have 1 million cars that potentially could use a given roadway like Edsa on a given day. If we ban 20% of them on that day using Number Coding, then only 800,000 of them could potentially be on Edsa, giving us a nice feeling that we have prevented a potentially greater traffic congestion.

But now think of what happens a few years later in Year Two, when we might have 2 million cars that potentially could use Edsa on a given day.  Under Number Coding, 20% of them are banned from Edsa on that day, so only 1, 600,000 of them are potentially going to be on Edsa that day, giving us a nice feeling that we have prevented a potentially greater traffic congestion. [sic!]


So, does Number Coding actually reduce the traffic volume or number of cars on Edsa on that day in either Year One or Year Two?

Well, in Year One 800,000 cars could potentially be on Edsa when Number Coding is in effect, while in Year Two 1.6 million could potentially be on Edsa on that week day.

So there is a reduction in potential traffic volume on both days equal to 20% of TWO DIFFERENT TOTALS but the potential traffic volume on the roadway increases continuously with the population growth rate of the vehicles that potentially could be on it on any given day! (Until, of course, it reaches the maximum physical carrying capacity of the roadway.)

Number coding is a Mental Scam! Over any finite length of time,  there is NEVER a Reduction in Volume or Number of Vehicles potentially present on a given roadway on a given week day, year on year, even with 100% Compliance with Number Coding. This is because Number coding allows a fixed 80% of the more or less constantly increasing total number of licensed vehicles to be on the road on any given weekday.

5 comments:

Ben Vallejo said...

They also should study geography! There is a spatial limit to roads that can be built.

Singaporeans have realized this. No one has the automatic right to own a car. A Singapore resident has to bid for this and then buy one at expensive prices.

The government should limit car ownership. Owning one per family may exempt an owner from surcharges but the second should be horribly taxed at every car re-registration. It is the motor vehicle analogue of China's one child policy.

Dean Jorge Bocobo said...

A warm welcome, Ben! Good thoughts from you as always.

Trosp said...

“Number coding is a Mental Scam. There is NEVER a Reduction in the Volume or Number of Vehicles potentially present on a given roadway--even with 100% Compliance with Number Coding.”

Does it mean the 20% reduction does not happen? Do those 20% did not comply?

“So there is a reduction in potential traffic volume on both days equal to 20% of TWO DIFFERENT TOTALS but the potential traffic volume on the roadway increases continuously with the population growth rate of the vehicles that potentially could be on it on any given day! (Until, of course, it reaches the maximum physical carrying capacity of the roadway.)”

I can say that it is a fact there is a reduction in traffic volume even we use a remedial math computation. There is no need to use the term “potential”. No matter what the traffic volume is, it is always less 20% if number coding is in implementation..

IMO, as for this method as the best solution for traffic congestion in Metro Manila is another thing.

Dean Jorge Bocobo said...

Trosp,
The way to see my point in this post is to ask 20% of What? Think of two different Mondays. The number of excluded vehicles is 20% of a different number on one Monday compared to the next. Same 20% different base, always increasing.

But even if you consider just one Monday, as I think you are doing, and ask whether 20% actually are excluded, there is something wrong. Because of the phenomenon of replacement. It's like if we had number coding to control the demand on food. Even if we can't eat once a week, we will make up for the deficit in the other days. In traffic, suppose I have to run an errand on my coded day. I just run in on a noncoded day. But that adds to the traffic on a coded day which would not have happened had I been allowed to do the errand on my coded day. So reduce the reduction by all trips that can be done at a different day. Next, everyone who has one car, wants two and eventually gets it! Reduce the reduction by all who own two or more cars!. There are many other exceptions until you get to the rub: Number coding only affects the lower middle class who simply must use their one car to go to work and bring kids to school! But 20% reduction in potential traffic? No way.

Trosp said...

"The way to see my point in this post is to ask 20% of What? Think of two different Mondays. The number of excluded vehicles is 20% of a different number on one Monday compared to the next. Same 20% different base, always increasing."

Is it?

There could be an increase the way you observed it (and I know your mind is already made up on that issue) but look at the plate numbers of the cars on the road within the coding implementation time. Are those banned still plying on the road?

The number could be 500 on one Monday less 20% = 400 and a million on the other Monday less 20% = 800,000.

The bottomline:

- If those 20% are out of the road as in coding implementation, then the there is this 20% reduction.

- If they're not (violating the coding implementation), then there is no reduction.

The way I see it, you are interpolating while on my part I'm just calling it straight.