The paper reports on the measurement and evaluation of the group velocity (GV) dispersion in the proximity of the cutoff wavelength for the fundamental photonic bandgap mode in a 2D photonic crystal waveguide (PCW). The PCW is created by introducing a line defect in an otherwise perfect triangular lattice of air-holes in the 216-nm thick silicon layer in an SOI material. Experimental transmission spectra show a mode cut-off around 1562.5 nm for the fundamental photonic bandgap mode. In order to measure and model the group index of modes in the PCW, a time-of-flight (ToF) method is applied.