前 and 手前: in front of something and on the near side
Compare a position in front of a building with a point before reaching it, keeping the reference object and approach direction clear.
In front of the reference object
前, read まえ, identifies the front of a reference object. 劇場の前に噴水があります。 says that there is a fountain in front of the theater.
受付の前で待ってください。 asks someone to wait in front of the reception desk. Use 受付 as the reference rather than substituting the speaker.
Before reaching a reference point
手前, read てまえ, is the near side of a point relative to the viewer or approach. 橋の手前で車を止めました。 says that the car was stopped on the near side of the bridge.
店の手前の角を曲がってください。 asks someone to turn at the corner before reaching the shop. This differs from turning after passing the shop.
Placing different reference points on a map
門の前 locates something in front of the gate; 門の手前 places it before the gate along the approach. They may identify the same spot, but their reference relations differ.
橋の手前まで来ました。 says that someone came as far as a point before the bridge. It does not state that the bridge was crossed.
Does 橋の手前で待っています。 place the person beyond an already crossed bridge?
Show the answer and why
No such conclusion follows. Here 手前 identifies a point before reaching the bridge along the approach.