For trucking, the time before and after holidays often means traffic is heavier at times and this Thanksgiving may be a whopper in some places.

A provider of traffic information and driver services, Inrix, says on Wednesday, in advance of the Thanksgiving holiday, travelers can expect trips in major cities to take a third longer on average due to increased traffic congestion, while other areas of the country, where economies are still struggling, can expect to see less traffic congestion over the Thanksgiving holiday.

The Wednesday pre-Thanksgiving rush hour should begin two hours earlier than a typical Wednesday in most cities. Rush hour should peak between 2 p.m. and 6 p.m. in the bigger cities and 2 p.m. and 5 p.m. in the smaller cities. Traffic should drop off quickly after 6 p.m. On the West Coast, traffic congestion is expected to build as early as 1 p.m. but on the East coast and in the Midwest, traffic is expected to build starting at 3 p.m.

Traffic this Thanksgiving is expected to be greater than last year due to the average cost of gasoline being down about 25% compared to a year ago.

Los Angeles, New York, Seattle, and San Francisco top this year's list of worst traffic cities with trips out of town taking from 30% to 50% longer than a typical Wednesday afternoon. 

The chart below shows the peak congestion period and extent of delays for the 10 worst cities. 

*Large shifts in congestion in New York and Portland compared to last year are attributed to the impacts of weather events in those areas.

NRIX also analyzed traffic levels around America's busiest shopping centers over the last three years to predict what drivers can expect travelling around these areas on Black Friday. It forecasts traffic congestion will peak between 1 p.m. and 5 p.m.

The following table tracks the Top 10 Busiest U.S. shopping centers, the peak congestion hour and the percentage change over 2012.