1
There were too many traffic on the road this morning.
There was too much traffic on the road this morning.
Traffic is an uncountable noun. Use a singular verb and much, not many: ‘There was too much traffic.’ You can also say ‘There was a lot of traffic.’
2
I was late because of a traffic.
I was late because of the traffic.
Traffic is uncountable, so we cannot say ‘a traffic’. We can say ‘because of traffic’ or ‘because of the traffic’. We can also say ‘because of a traffic jam’.