The road over Cherry Brook Bridge

In this photograph Robert Burnard can be seen standing on the road over Cherry Brook Bridge sometime in December 1887. This road is now the B3357 between Dartmeet and Two Bridges. Cherry Brook Bridge is a double arched turnpike period bridge and has a buttress on either side. Are the ragged rows of granite posts on both sides of the road guides to help funnel animals being driven over the bridge or track markers when snow covered Dartmoor?