Skyhawk 172/Cutlass 172
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 30; Flight Crew Total 950; Flight Crew Type 620
Confusion; Situational Awareness
Ground Incursion Runway
Air Traffic Control Issued Advisory / Alert
Airport; Human Factors; Procedure
I'm writing to call your attention to a potentially unsafe condition at Long Beach; CA airport (LGB). LGB's runway pattern consists of four about 6;000 FT runways formed in a rectangle bisected at two corners by a longer about 10;000 runway; Runway 30/12. Runway 30/12 is sufficiently long that its two end sections protrude well outside the 'rectangle' formed by the smaller runways; and are themselves sufficient to land a C-172 on. In this case I completed an ILS approach to Runway 30; landed at the numbers; and then turned off to the left at the first opportunity. This opportunity turned out to be the displaced threshold area for Runway 25L. The Tower noted very nicely: 'We don't do that here;' and gave progressive instructions to a connecting taxiway. I note the following: (1) there was no double yellow line prohibiting such a turnoff; (2) just beyond Runway 25L there is a taxiway parallel to Runways 25; however; the signage is dense and the directions of the taxi arrows are ambiguous; and (3) given traffic at LGB consists in good part of closely spaced jet traffic; it is a great idea to exit the 'active' quickly. I learned later; upon departing the next day; that both Runway 30 and Runway 25L are often BOTH active. Obviously; it is not a great idea to have aircraft taxiing through the threshold area for an active runway. Upon further investigation; I learned LGB is Number 5 in the frequency of runway incursions nationwide; so I'm guessing I'm hardly the first person to have expressed concern. Possible mitigations; none perfect; include:--painting a double yellow line across where the threshold to Runway 25L crosses Runway 30; --improving the signage; or worst of all; --closing Runways 25 when Runway 30 is active. By the way; this same situation exists at other corners of the 'rectangle' at LGB; too.
C172 pilot experienced a runway incursion at LGB.  Reporter stated confusing signage was a contributing factor.