Very short headways are controversial. The UK Railway Inspectorate has evaluated the ULTra design and is willing to accept one-second headways, pending successful completion of initial operational tests at more than 2 seconds.Sustainable personal transport In other jurisdictions, preexisting rail regulations apply to PRT systems (see CVS, above); these typically calculate headways for absolute stopping distances with standing passengers. These severely restrict capacity and make PRT systems infeasible. Another standard said trailing vehicles must stop if the vehicle in front stopped instantaneously (or like a "brick wall"). In 2018 a committee of the American Society of Mechanical Engineers considered replacing the "brick wall" standard with a requirement for vehicles to maintain a safe "separation zone" based on the minimum stopping distance of the lead vehicle and the maximum stopping of the trailing vehicle. These changes were introduced into the standard in 2021.
Very short headways are controversial. The UK Railway Inspectorate has evaluated the ULTra design and is willing to accept one-second headways, pending successful completion of initial operational tests at more than 2 seconds.Sustainable personal transport In other jurisdictions preexisting rail regulations apply to PRT systems (see CVS, above); these typically calculate headways for absolute stopping distances with standing passengers. These severely restrict capacity and make PRT systems infeasible. Another standard said trailing vehicles must stop if the vehicle in front stopped instantaneously (or like a "brick wall"). In 2018 a committee of the American Society of Mechanical Engineers considered replacing the "brick wall" standard with a requirement for vehicles to maintain a safe "separation zone" based on the minimum stopping distance of the lead vehicle and the, maximum stopping of the trailing vehicle. These changes were introduced into the standard in 2021.