Vehicle article carrier with supports configurable as elevated side rails or flush mounted slats

A vehicle article carrier system (10) having an elongated siderail (16) which can be configured in a first configuration as a slat of the system or in a second configuration as a siderail of the system. The elongated support rail requires no modification before same can be used in either a slat-based or a siderail-based vehicle article carrier system (10). Either configuration can be used to support one or more cross bars and conventional bracket assemblies directly on the support rails.