道路 and 歩道: a road and its pedestrian portion
Compare a road with the sidewalks beside it, reading sidewalk width, walking routes, and the target of a vehicle restriction.
A road used by people or vehicles
道路, read どうろ, means road. 学校の前に広い道路があります。 says that there is a wide road in front of the school.
道路の端に標識が立っています。 says that a sign stands at the road’s edge. It identifies the sign’s position rather than reporting what the sign says.
A portion provided for pedestrians
歩道, read ほどう, means a sidewalk or pedestrian portion of a road. 道路の両側に歩道があります。 says that sidewalks run along both sides of the road.
この歩道は幅が狭いです。 says that this sidewalk is narrow. It describes the sidewalk’s width without assigning that width to the entire road.
The whole area and the target of a notice
歩道を歩いて店へ行きました。 says that someone walked along the sidewalk to the shop. 歩道を is the walking route, and 店へ the destination.
歩道に車を入れないでください。 asks people not to bring cars onto the sidewalk. Keep its stated targets, 車 and 歩道, rather than extending it to every activity on the entire road.
Does この歩道は幅が狭いです。 establish that the whole road is narrow?
Show the answer and why
No. The specified narrow part is the sidewalk. The road’s overall width needs separate information.