The Alexander ALX500 (later known as the TransBus ALX500) was a low-floor double-decker bus body built by Alexander in Falkirk, Scotland between 1997 and 2002.
The Alexander ALX500 was fitted to Dennis Trident 3 and Volvo Super Olympian chassis (they could be distinguished by the design of the engine compartment: with round indicators for Dennis and square indicators for Volvo), and came in lengths of 10.6, 11.3 and 12 metres (35, 37 and 40 foot). The ALX500-bodied buses were sold new to Citybus, Kowloon Motor Bus, and Kowloon-Canton Railway Corporation in Hong Kong. Due to the climate there, all of them were fitted with air conditioning systems, and as a result lacked a rear window on the lower deck. The extra length of the buses mean the seating capacities were near the 100 mark for the 12.0 metre variant.
left|thumb|[[Long Win Bus Alexander ALX500-bodied Dennis Trident 3 rear.]]
Alexander built three prototype ALX500 bodies for prototype Trident 3 chassis. The first prototype, built in 1995, had an Alexander R-Type front fitted as a temporary measure, whilst the other two had the standard ALX range front design. Production of the ALX500 body was started later in 1997 on Trident 3 chassis, with two examples exhibited in Coach & Bus '97 in Birmingham; but there were some minor changes in appearance, for example the exit door was moved rearward (for 12.0 metre variant only).