The noun necessity can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be necessity. However, in more specific contexts, the plural form can also be necessities e.g. in reference to various types of necessities or a collection of necessities.

Is necessity a countable noun?

[countable] a thing that you must have and cannot manage without Many people cannot even afford basic necessities such as food and clothing. ... [countable, usually singular] a situation that must happen and that cannot be avoided Living in a big city, he felt, was an unfortunate necessity.

Do you say need or needs?

If "Highway 68 and Robinson Canyon Road" is conceptualized as a single project in need of support, then the singular verb (needs) could be used. If the two roads are conceived as separately in need of support, then the plural need is used.