Dijkstra openmp code in c

Hi i work on openmp and want to test a code of dijkstra algorithm.The code is heredijkstra_openmp .This code is written by John Burkardt and i try to run it.But run time for 1 thread is same by four thread.I have a intel core i3 system that can support 4 threads.I need a test case for it to estimate speed up of code. Available test case is too small.