This example shows the monthly regularity of TGV trains on French routes, displayed as a bar chart of the number of delayed trains per month. It begins by filtering a CSV of train records (tgv_annees.csv) to a selected origin–destination pair and year, then renders the resulting monthly counts as labeled bars using SVG. The visualization is built with D3 v4, using `d3.csv` for loading, `d3.scaleLinear` and `d3.scaleBand` for axes, and `d3.axisBottom` for the month labels. The code follows a reusable chart module pattern, with the main chart logic in `histogram-chart.js`.