**2. Control policies for the lifts' systems**

There are many various control rules for the lifts'systems. We will consider only some of them, for instance, the *Odd-Even* system, where some lifts serve customers at the odd floors and other lifts, at the even floors. Another control rule, we call it following to [4], the *Up-Down* system, where some lifts serve customers going from the first floor to the Down floors *1, 2, … , k,* others serve customers going from the first floor to the Upper floors*1, k + 1, k + 2, … , n*. This control was introduced in [5]. For some systems by simulation, the numerical values of optimal *kopt.*, which minimize the value of *CWT,* was found. All these control rules can improve the service, i.e. to reduce the customer's waiting and service times and also diminish energy expenses. Some methods of investigation of queues with a finite service capacity can be used for the research of the lifts'systems [8].

An interesting unofficial control policy was created in the seventy years of the XXth century, by the students in the dormitory of the Moscow Lomonosov State University. There are 18 floors in the student dormitory and two lifts' halls with four lifts in each. The first lift hall operates from the *1st to the 12th, 14 th, 16th* *Estimation of the Efficiency Indices for Operating the Vertical Transportation Systems DOI: http://dx.doi.org/10.5772/intechopen.94066*

*and 18th* floors. In order that the lifts work more rapidly, it was skipped the odd numbered floors, after the 12th. There is also a second lift hall for serving on the 1st-10th floors. If in the first hall, a lift came to the first floor and the first student yelled the word *"Higher",* then, the lift would be filled by students who are going up only to the higher floors *(16th and 18th)* and the next lift will be filled by students who are going to the *12th, 14th, 16th* floors and upper. If the first call had been *"LOWER",* then the lift would have operated between the lower floors (*12th, 14th* and afterward, to the other upper floors). The students called it a *Higher-Lower* system.

In [7], it was introduced the so called "situation control rule" for systems with two lifts. If both lifts are going from up to down, then all arrived customers (at the different floors) will be distributed between lifts. This control rule allows to exclude stopping both lifts almost at the same time, at the same floors. Such systems work effectively for high intensity of customers' flows. For instance, if both lifts are going from up to down, then each lift system defines the floors where the lift must stop and serve the customers. In the case of a customer's arrival at the new floor system, it must be recalculated the number of the floors where the lift must stop. Such a control rule allows using lifts capabilities in a uniform way. Although the "situation control rule" needs some additional software and technical equipment, nevertheless it improves the service (reducing customer's waiting and service times), it saves energy expenses and increase the lifetime of the lifts.
