I would like to discuss the difference between the usage in these sentences below:

I was delayed by a traffic jam.
I was delayed by heavy traffic.

The second one is correct, based on a TOEFL test sample. I also wonder why the sentence below is incorrect in the test:

I was delayed by a heavy traffic

Both traffic jam and heavy traffic are objects. I know the preposition a must be put before traffic jam in this example, because the event is specific.


In the first example you were delayed by a jam, that is a hold-up when the traffic either doesn't move or creeps forward. Jam is a countable noun. You can have multiple jams or traffic jams.

In the second example you were delayed by traffic, an uncountable noun. We don't use a or an ahead of uncountable nouns. They can stand alone or be used with the definite article the.

(The) traffic was heavy; that's to say the roadway was very busy.

However there wasn't a hold up although your sentence indicates that the intensity of traffic had forced vehicles to slow down.


  • Regards Ronald, and thanks. If traffic is a system of moving vehicles, then i could say : 'I was delayed by a traffic (in town A)'. The traffic can be different for each region. If this is not the case, then i presume that 'traffic' is as similar as 'mathematics' in 'His graduation was delayed by difficult mathematics.' – Arief Anbiya Mar 25 '17 at 16:21
  • 1
    @Arief.an We don't use the indefinite articles a or an before uncountable nouns. For instance, you can say water had flooded the town or the water had flooded the town (but not a water). Thus, you can be delayed by a jam but not by a traffic although you can be delayed by the traffic. – Ronald Sole Mar 25 '17 at 16:28
  • Ronald, milk is uncountable (as liquid), but if it means as packaged milk, then it cam be counted. May i refer this Link . I presume traffic can be viewed as a unique system in a particular area. – Arief Anbiya Mar 25 '17 at 16:52
  • 1
    There are contexts in which an indefinite article can precede an uncountable noun: a fog of doubt, an air of puzzlement....and so on. But the general rule holds. The traffic refers to a system in a particular are: the traffic downtown. *Traffic can be used in any context: Traffic across the country/continent was affected by the weather. – Ronald Sole Mar 25 '17 at 17:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.