A traffic chart is a graphical representation of the flow of traffic in a given area. It is typically used to identify areas of congestion or potential safety hazards. The term 'traffic chart' can also refer to a GRID-like diagram that shows the number of vehicles passing through an intersection at different times of the day. This type of chart is often used to help plan traffic control measures, such as the installation of traffic lights or the introduction of one-way streets. The four-letter solution to the crossword clue is GRID.