And a big thanks to Brian for his comments. He wrote a lot, but in his conclusion he suggested:

To improve quickly I guess [you] just need to put one point in one sentence then support them. Then break down long sentences. It helps you focus on the whole meaning of the sentence  whether it makes sense or not. Put your idea as clearly as you can.

I'd agree with him 100% - some of the sentences are indeed long.

But one thing I didn't like in the last part of Paragraph Two was the pronoun and pronoun reference. I was jumping all over the place trying to work out what these were:

Increasing the price of petrol is definitely one of the most effective solution, although it presents several drawbacks. Indeed, though it leads people to use less their car in order to save money, on the other hand many people cannot avoid driving to reach their work places.  Hence, these categories undergo the rise of the price of the fuel more than others and it is not fair. Moreover, particular activities must be mentioned such as delivery and transport of goods. These ones, in fact, are the most affected groups and sometimes, as a result, massive general strikes against that increase occur, affecting everyone's daily routine very deeply. (107 words)

Don’t use Although/On the other hand or Although/but in the same sentence. Try to avoid passives (‘must be mentioned’)

Here’s one possible rewrite. I’ve tried to clarify or remove the confusing pronoun references.

Increasing the price of petrol can definitely be effective, although it presents several drawbacks. Indeed, although higher fuel prices might encourage people to use their car less often in order to save money, most people cannot avoid driving to work. Hence, commuters would suffer unfairly from the price rise. Moreover, essential services such as transport and goods delivery would become more expensive, affecting the economy. (65 words)

Try to keep your writing going forward. Don't make the reader go back: keep pronoun reference clear and simple. The reader is a goldfish: just guide us along in a nice straight line to the end, and don't force us to remember everything!

Shorten/Simplify

Having fewer words in your sentences means you can have more ideas and examples. Content is king!

 You wrote a 34-word sentence here:

Furthermore, regarding to traffic congestion, a practical suggestion might be to order citizens to use their vehicles only in those days established by general rules: car's number is generally the most common criteria that can be used. (34 words, 1 sentence)

'Car's number' should be changed to 'car numbers.' Here’s one possible rewrite:

Furthermore, to reduce congestion, a practical suggestion might be to allow vehicles only on particular days, times or places. In Rome, for example, only even car registration numbers are allowed on specific days. (33 words, 2 sentences, average 16.5 words per sentence.)

OR

One suggestion might be to allow certain vehicles only (e.g. with odd or even numbers) on particular days. (18 words)

Word Choice/Word Form/Usage

• Not only do metropolitan centres cope with them, but they are becoming a serious threat even to smaller towns. (19 words)

‘Cope’ is not quite correct – it usually means to manage successfully. We need to make it a little more negative: 

Not only do metropolitan centres have to cope with them, but they are becoming a serious threat even to smaller towns.  OR 

Not only do metropolitan centres have to deal with them, but they are becoming a serious threat even to smaller towns.  (21 words)

OR

Both cities and smaller towns are having to deal with increased traffic and pollution (14 words)

• both national and local governments have been introducing recently different kinds of policies with which tackle those growing troubles.  → both national and local governments have been introducing different kinds of policies recently with which to tackle those growing troubles.

Brian also suggested fewer nouns, and I agree again.

This sentence is not wrong but it's always useful to see if you can express yourself more succinctly.

• to reach their work places.  → to reach work/to go to work

Again, shorter sentences would give you an opportunity to present more ideas and examples. You have two ideas in Paragraph Three - three would be better. Don't be afraid to give relevant concrete examples from your 'knowledge or experience' - it's interesting to see examples from countries or cities you know.

Great essay . Id like to leave some comments on your essay. I hope you will find the useful.

Pollution and traffic congestion are nowadays two of the main problems which affect cities and their citizens. Not only do metropolitan centres cope with them, but they are becoming a serious threat even to smaller towns. Therefore, both national and local governments have been introducing recently different kinds of policies with which tackle those growing troubles.

***Not only ... but also is Parallelism.. the verb must be in same forms to make a correlation.Example:

He’s not only funny, but also he’s intelligent.

When using a correlative conjunction, both clauses have to be parallel.

Today pollution and traffic congestion are two of the main problems which affect cities and their citizens. Not only they involve metropolitan centres in some serious problems, but also pose a  threat to smaller towns. Therefore, both national and local governments have been introducing different policies to tackle those growing troubles.

Increasing the price of petrol is definitely one of the most effective solution, although it presents several drawbacks. Indeed, though it leads people to use less their car in order to save money, on the other hand many people cannot avoid driving to reach their work places. Hence, these categories undergo the rise of the price of the fuel more than others and it is not fair. Moreover, particular activities must be mentioned such as delivery and transport of goods. These ones, in fact, are the most affected groups and sometimes, as a result, massive general strikes against that increase occur, affecting everyone's daily routine very deeply.

** be more academic. Not to be too general.( definitely? how do you prove that)

** Do not put more two or more points in one sentence. As official IELTS says you should support your claims ,putting such points in one sentence make your sentences longer. Moreover you have to put more efforts to supports them. This makes your sentences awkward . Use less nouns (the rise of the price of the fuel)

Remember that the examiner is not patient enough to think what are you saying!!! Making your last sentence easy to read.

Although increasing the price of petrol would be one of the most effective solutions, it presents several drawbacks. In fact it leads people to use less their cars and, therefore, saves more money.But many people cannot avoid driving to reach their work places. And they should endure rising fuel price. It becomes even worse for other groups whose their jobs are delivery and goods transportation. No wonder those groups who their  life are adversely affected by this increasing, may  go on strike. And this is a vicious cycle as affecting the rest of people's daily routine.

For these reasons, I believe that increasing the price of fuel cannot be the only answer to pollution problem. Rather, governments should intervene in many other ways which might help in solving it. For instance, they could introduce new tax for green houses' activities, which nowadays represent a determinant cause of air pollution. Furthermore, regarding to traffic congestion, a practical suggestion might be to order citizens to use their vehicles only in those days established by general rules: car's number is generally the most common criteria that can be used.

Last but not least, increasing the price of fuel cannot be the only answer to pollution problem. Instead, governments should take some steps in this case. For instance, they could introduce green taxes on carbon emissions . Ans also to reduce the carbon footprint they can encourage people to use less private cars only in those days already defined by public rules, and the rest of the days use carpooling. ( I think you easily could put more solutions like public transportation ......)

In conclusion, I think that to solve traffic and pollution problems, several measures need to be sorted out, besides increasing the price of petrol. What is more, a strict control by authorities on dwellers's behaviour must be guaranteed to make those measures really efficacious.

**You put a new idea in your conclusion. what strict controls do you mean? you didn't explain them!!! Almost in every paragraph you left ideas without any supporting.

Your essay if good. To improve quickly I guess just need to put one point in one sentence then support them. Then break down long sentences. It helps you focus on the whole meaning of the sentence  whether it makes sense or not. Put your idea as much as you can clearly. Hope to find my comments useful. I think Mr.Enda  has better ideas and comments to both of us.

Best regards,

Pollution and traffic congestion are nowadays two of the main problems which affect cities and their citizens. Not only do metropolitan centres cope with them, but they are becoming a serious threat even to smaller towns. Therefore, both national and local governments have been introducing recently different kinds of policies with which tackle those growing troubles.

Increasing the price of petrol is definitely one of the most effective solution, although it presents several drawbacks. Indeed, though it leads people to use less their car in order to save money, on the other hand many people cannot avoid driving to reach their work places. Hence, these categories undergo the rise of the price of the fuel more than others and it is not fair. Moreover, particular activities must be mentioned such as delivery and transport of goods. These ones, in fact, are the most affected groups and sometimes, as a result, massive general strikes against that increase occur, affecting everyone's daily routine very deeply.

For these reasons, I believe that increasing the price of fuel cannot be the only answer to pollution problem. Rather, governments should intervene in many other ways which might help in solving it. For instance, they could introduce new tax for green houses' activities, which nowadays represent a determinant cause of air pollution. Furthermore, regarding to traffic congestion, a practical suggestion might be to order citizens to use their vehicles only in those days established by general rules: car's number is generally the most common criteria that can be used.

In conclusion, I think that to solve traffic and pollution problems, several measures need to be sorted out, besides increasing the price of petrol. What is more, a strict control by authorities on dwellers's behaviour must be guaranteed to make those measures really efficacious.