Input (grade 12): The first journey took 12 minutes northbound and 10 minutes to return, even allowing for the horse-drawn vehicles also using the roads on the overground part of the route.
Output (grade 7): The first journey took 10 minutes to go to Aldwych and 12 minutes to get back. This was also allowing for the horse-drawn vehicles that were using the roads on the overground part of the route.