'Traffic' is an example of an English uncountable noun. We cannot say 'a traffic' or 'three traffics'. You need to learn the most common uncountable nouns:
accommodation
advice
behaviour
commerce
data
education
equipment
furniture
information
knowledge
money
news
permission
progress
research
scenery
staff
travel
trouble
vocabulary
weather
work
Note that many uncountable nouns can be 'counted' using an extra noun:
A piece of advice
An item of equipment
Compare:
All universities conduct research (in general)
The research I began four years ago (specific)
In American English there is a tendency to use certain nouns in the plural e.g. behaviours, accommodations.
Also, note that some nouns can be both countable and uncountable. These are often words for general concepts e.g. love, life, war, death:
Love is a powerful emotion (uncountable)
He had three great loves: his work, his garden and his dog (countable)
