They might follow the plan used with the Cambridges and the Wessex weddings and not use carriages on the way to the church. They might opt to transport everyone (Cambridge wedding) and Wessex (bridal party) to the venue via car. (The royals walked to St. George's chapel for Edward and Sophie's wedding.) The Cambridge wedding saw the coaches/landaus used on the return trip and the Wessexes went through Windsor in a landau after their wedding