Small aircraft pilot reported while holding short at a taxiway; another aircraft came extremely close in proximity as it was taxiing. The other aircraft was taxiing at a fast speed and the reporter had to quickly stop while over the runway hold-short markings to avoid a collision.

Narrative

After landing on Runway 28 at Allegheny County Airport; AGC; I received instructions from the Control Tower to exit at A3; hold short of Taxiway A; and contact Ground. After making the left turn onto A3; I visually acquired the runway hold-short markings and noted how close they were to Taxiway A. Knowing an airplane was on final for Runway 28; I wanted to ensure I exited the runway by completely crossing those markings. As I was crossing the markings; which were very close to Taxiway A; I looked to my right and was surprised to see a fast-moving Aircraft Y taxiing eastbound on Taxiway A approaching my airplane. With the tail of my airplane still over the runway hold-short markings; I immediately stopped and noticed my propeller was very close to the edge of Taxiway A. As Aircraft Y passed my airplane; its left wing came within two feet of my airplane's propeller. Since there was no mention of holding short of Taxiway A for a taxiing airplane; I cleared the runway as normal. If that information was provided; I would have been more vigilant looking for the taxiing airplane while exiting the runway.The boundary of Taxiway A; Taxiway A3; Runway 28/10 and Runway 31/13 is designated as a Hot Spot because there's very little space there. That area is very dangerous and an inexperienced pilot or a pilot not paying attention could get confused at that location. There is no need for A3 and I believe its removal would prevent any future incidents or accidents.