[cmul]

Imho, the major constraint for railways in most countries is policy, not technology. In the US and many large (surface area) countries, railways primarily serve for freight transportation and, to a shockingly underdeveloped degree, local commuters. In Europe legacy solutions and differences of national systems, planning guidelines and even power grid cause problems. Some nations' railways are extremely underfinanced and have been driven to the brink of collapse in the privatizations of the early 90s with more than 30 years of missed investments. The rollout of ETCS tries to remedy that and so do ERA/EUG/ERJU but the coffers of many nations are rather empty/respectively other interests weigh higher (subsidies for streets, automotive companies, aviation and other big buckets like farming).