Editing Personal rapid transit (section)

====Headway distance====
Spacing of vehicles on the guideway influences the maximum passenger capacity of a track, so designers prefer smaller [[headway]] distances. Computerized control and active electronic braking (of motors) theoretically permit much closer spacing than the two-second headways recommended for cars at speed. In these arrangements, multiple vehicles operate in "platoons" and can be braked simultaneously. There are prototypes for [[autonomous car|automatic guidance of private cars]] based on similar principles.

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.<ref>[http://www.advancedtransit.org/wp-content/uploads/2011/08/Sustainable-personal-transport-M.-Lowson.pdf Sustainable personal transport]</ref> 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.<ref>{{cite web |title=ASCE APM STANDARDS COMMITTEE ACCEPTS ALTERNATIVE TO BRICK WALL STOP |url=http://www.advancedtransit.org/library/news/asce-apm-standards-committee-accepts-alternative-brick-wall-stop/ |website=Advanced Transit |date=11 May 2018 |access-date=3 July 2021}}</ref>  These changes were introduced into the standard in 2021.