"walkers could proceed with the minimum of obstruction"

• a thing that impedes or prevents passage or progress; an obstacle or blockage

  "the tractor hit an obstruction"

• (in various sports) the action of unlawfully obstructing a player in the opposing team
• blockage of a bodily passage, especially the gut

  "they presented with severe intestinal obstruction"

• the action of impeding the movement of traffic on a highway

  "they were held for obstruction and other public order offences"

• the action of deliberately hindering the police in their duties

  "he was charged with obstruction of a police officer in the execution of his duty"