Learn Romanian: Lungimea acestui pod este din ce în ce mai mare. - The length of this bridge is getting bigger and bigger.

It is a fixed phrase used to express a progressive increase, translating to "increasingly" or "-er and -er". Literally meaning "from what in what more", it is always followed by an adjective or adverb. Together with mare, it means "bigger and bigger".

Why do we use acestui instead of just acest?

We need the genitive (possessive) case here to mean "OF this bridge". Because pod is a neuter noun, its demonstrative adjective placed before the noun takes the masculine/neuter genitive form, which is acestui.

Is it possible to place the word for "this" after the noun instead?

Yes, but both words would change. When the demonstrative follows the noun in the genitive case, the noun takes the definite article (podului) and the demonstrative takes its longer post-position form (acestuia). Using acestui pod is often easier because the noun itself doesn't change.

Why does mare not have a specific feminine ending to agree with lungimea?

The adjective mare belongs to a class of Romanian adjectives that share the exact same form for both masculine and feminine in the singular. It only changes in the plural (becoming mari), so it is already in the correct form to agree with the feminine noun lungimea.