As she approached Fort Detrick, in the city of Frederick, the traffic thickened and slowed.

Here the traffic was thickening like milk soured by lemon juice.

The sky above the crowded rooftops was blue now, and traffic was thickening along the road.

Local traffic has thickened and shopping centers have mushroomed on the main drags.

The sun was long down and traffic had thickened.

The traffic thickened as Washington opened up for business.

Most of the roads that he chose were well-paved, but only for a short stretch did he follow a course where traffic thickened.

Under the clear summer morning sky the traffic thickens.

As the traffic thickened towards the rush hour it got easier, but more boring, to stay fairly close behind him.

Then the traffic between them had thickened, and he'd disappeared.