Despite the unscheduled stop the royal couple transferred to cars and continued on to the market town of Hay-on-Wye by road.
They finally arrived close to three hours late but emerged looking relaxed and smiling to be greeted by a crowd of several hundred well-wishers.
More top news
Brent Stirton won the Wildlife Photographer of Year award for his image Memorial to a Species, taken at a game reserve in South Africa.
Analysis of queues found drivers faced 1.35 million traffic jams, costing them in wasted time, fuel and unnecessary carbon emissions.
It will be a cloudy day across much of Wales, central and southern England with outbreaks of rain and drizzle.