all public transport services in a given area. A characteristic of integrated clock-face timetables is that there is more than one central hub. A hub-and-spoke approach is then applied to the whole transport network. Having several services meet at hubs where all of them arrive and leave at the same time is the most effective way of connecting multiple routes and modes. The goal is to reduce transfer times to a few minutes, with a default time of no more than five minutes. In actual operation, the time span can be longer because of services running early or late, high passenger volume (such as rush hour), or the need to assist passengers with disabilities. Efficient operation is even more essential than normal with integrated clock-face timetabling. If the policy is to hold connecting services to ensure a connection with a late-running service, waiting times at interchange stops can become unattractive, and other services will run late as a consequence. Examples of such networks are often night and city bus networks. The connections might be optimized only within the network but not for transfers to rail or intercity bus lines. Such concepts need purpose-built stations, which can handle high passenger volumes. The space constraints within cities can be a reason to use other concepts. An integrated regular timetable with half-hourly or hourly headways requires routes on which a service ideally takes 28 or 58 minutes to make it from one hub to another (accounting for two minutes of changing and waiting time at the hub). A service that takes 40 minutes would be bad because passengers and vehicles have to wait uselessly for their connections (unless the timetables at the different hubs are offset from each other to compensate, which is only practical for networks with very few hubs), and it generates nearly the same cost as a route that takes 58 minutes because vehicles and personnel cannot be used during the remaining 20 minutes. Therefore, when an integrated timetable is introduced running times might be cut or extended to meet the ideal duration. Emergence of integrated timetables The first integrated regular timetables were developed for railways. After the successful introduction of a line-bound regular timetable on one line in Switzerland in 1968, the development continued in the Netherlands. In 1970 and 1971, the Dutch Railways introduced a regular timetable with multiple hubs. In Germany, the first large-scale use of regular