Question

Motorists in a certain country frequently complain that traffic congestion is much worse now than it was 20 years ago. No real measure of how much traffic congestion there was 20 years ago exists, but the motorists’ complaints are almost certainly unwarranted. The country’s highway capacity has tripled in the last twenty years, thanks to a vigorous highway construction program, whereas the number of automobiles registered in the country has increased by only 75 percent.

Which of the following, if true, most seriously weakens the argument?

(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)

Solution

Understanding the Passage

Motorists in a certain country frequently complain that traffic congestion is much worse now than it was 20 years ago.

Motorists frequently complain
What do they complain about?
They complain that traffic congestion – now is much worse than traffic congestion – 20 years ago

No real measure of how much traffic congestion there was 20 years ago exists,

There is no way to quantify the traffic congestion 20 years ago. (So, perhaps, it’s difficult to ascertain whether motorists’ complaint is justified)

but the motorists’ complaints are almost certainly unwarranted.

The “but” indicates a contrast. The contrast is that while it’s difficult to quantify traffic congestions 20 years ago (thus it’s difficult to ascertain how true the complaints are), the complaints are almost certainly unjustified.

(Since the author has taken a stand in contrast to what can be expected, I expect the author to support his point in the coming statements)

The country’s highway capacity has tripled in the last twenty years, thanks to a vigorous highway construction program, whereas the number of automobiles registered in the country has increased by only 75 percent.

This statement supports the author’s stand (the motorists’ complaints are almost certainly unwarranted).

This statement says that the highway capacity has grown to 3 times the capacity 20 years ago while the number of vehicles registered has grown to only 1.75 times its number 20 years ago.

(How does it support the author’s stand? The underlying logic is that since the growth in highway capacity is greater than the growth in the number of vehicles registered, there is more highway capacity now than there was 20 years ago per vehicle registered in the country. Thus, there should be less congestion now than there was 20 years ago.)

The Gist

Motorists complain that traffic congestion is much worse now than it was 20 years ago.
The complaints are unjustified.
Why?
Because the highway capacity has grown to 3x the capacity 20 years ago while the number of automobiles registered has grown to 1.75x (less than 3x).

The GAPS

We find gaps by thinking how traffic congestion can be much worse now than it was 20 years ago despite the fact that highway capacity has grown at a faster rate than the number of registered automobiles.

Here are a few gaps that I could identify:

Perhaps, a lot of people are driving unregistered automobiles.
Perhaps, registered automobiles are driven much more now than they were 20 years ago (more traffic per automobile)
Perhaps, the number of scooters has increased to 10x in the last 20 years (scooters are not considered automobiles but can contribute to traffic congestion).
Perhaps, the additional highway capacity added in the last 20 years has been mainly along the routes that are not used much.
Perhaps, the non-highway capacity (inner roads in the cities) has not been expanded, resulting in traffic congestion inside the cities.

There can be more gaps in the argument. Can you think of any?

Evaluating the Options

(A) Correct.

This option is around the last gap that I identified above. (Are you wondering whether I thought of the gap after understanding this option? Are you accusing me of cheating? No problem. I did cheat 🙂

If most automobile travel is along the network of roads and streets that haven’t grown in the last 20 years, we have a reason to believe that traffic congestion is much worse now than it was 20 years ago.

Thus, the conclusion that the complaints are unwarranted stands weakened.

(I believe that some people reject this option, saying that this option strengthens the argument. This way of going wrong is quite frequent in arguments that follow the structure of this argument – Present X, Then, conclude X is not the case. X in this case is ‘traffic congestion is much worse now than it was 20 years ago’.)

In such arguments, some people consider an option supporting X to be a strengthener. That’s wrong. If an option supports X, it goes against the conclusion that X is not the case. Thus, that option is a weakener.)

(B) Incorrect.

This option is in line with the second gap I identified. (I didn’t cheat here 🙂

However, this option strengthens the argument rather than weakens it. If miles traveled per car hasn’t changed much in the last 20 years, we have more reason to believe that the traffic congestion is NOT much worse now than it was 20 years ago.

(C) Incorrect.

This option talks about the present scenario (“have”). It says that country’s urban centers have good public transport systems. In such a case, people don’t need to use their own automobiles to travel. Thus, instead of several automobiles (in case people travel in private automobiles), we have a bus or a train. So, this option indicates that there is perhaps less congestion than possible.

Thus, this option doesn’t weaken the argument.

(D) Incorrect.

This option has no impact on the argument.

Let’s first try to understand the meaning of this option statement. The option talks about the average age of automobiles registered in the country.

How do we calculate the average age of automobiles registered in the country?

We’ll sum the ages of all the automobiles registered in the country and divide this number by the number of automobiles registered in the country.

This average represents how old an average automobile registered in the country is. For example, the average age of 5 years means that automobiles are not very old (perhaps, the old vehicles are destroyed), whereas the average age of 15 years means that automobiles, on average, are quite old.

Is the average age of the automobiles, or how old the automobiles are, relevant to the argument?

Not at all.

(Not that it would matter, but it is worth noticing that the average age of vehicles doesn’t point to the number of vehicles on the road. The average age is a factor of how quickly old vehicles are discarded.)

(E) Incorrect.

Let’s consider the following statement:

E1: Motorists’ perceptions about traffic congestion are mainly based on traffic reports published by credible sources.

E1 is a weakener. By suggesting that motorists’ complaint is based on some authentic source of information, this statement weakens the conclusion that their complaint is unwarranted.

However, option E has almost no impact since option E doesn’t say that

the traffic reports published by radio stations are credible.
the traffic reports published by radio stations DO NOT differ in terms of whether traffic congestion has increased. (If they differ, then perhaps motorists’ perception is mainly a result of their biased focus on reports saying that the congestion has increased) [It’s important to be aware that option E says traffic reports inform about traffic congestion. The information could be that there is no traffic congestion.]
motorists’ perception of traffic congestion is not influenced much more by subjective factors than by these reports.

We can notice that while option E triggers you into thinking along the lines of E1, E is very different from E1. While E1 is a good weakener, E has almost no impact.

Chiranjeev Singh

An Alumnus of IIM Ahmedabad and with scores of 780 (2017) and 770 (2013) on GMAT and 99.98%ile on CAT, Chiranjeev is one of the most qualified GMAT tutors in India. Chiranjeev has earlier served as Director of Curriculum at e-GMAT. Chiranjeev has been helping students ace GMAT since 2012. He follows a concept-based methodology to teaching GMAT and is very committed to student success. You may contact him for any private GMAT tutoring needs at CJ@GMATwithCJ.com. He conducts online sessions for students across the world.

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