 After crossing an irrigation canal, Highway 40 turns north onto Arnold Road and crosses the CSX railway a third and final time before exiting Chatham–Kent.The route enters Lambton County in the municipality of St. Clair, passing through more farmland.north of the county line, the highway crosses the W. Darcy McKeough Floodway, a channel constructed in 1984 to protect Wallaceburg from flooding.