# A Comparative Study of the Availability of Electric Buses in the Public Transport System
## 1 Introduction  
The subject of the research described in this article is the availability (readiness) of electric buses as an important component of their operational quality in the public transport system [1, 2, 3]. Availability can be considered as a ratio of the expected uptime of a system to the total amount of observed time. The total amount of observed time is the sum of the uptime and downtime of the system. In reliability engineering, availability is expressed as a ratio of the Mean Time to Failure (MTTF) and the Mean Time Between Failure (MTBF). Depending on what is taken into account when determining the uptime and downtime, different types of availability are distinguished [4]. From the carrier's point of view, availability is one of the most important indicators characterising the operational quality of vehicles and the efficiency of the transport system [5, 6, 7]. Low availability in the transport system can have a significant impact by increasing costs within the company, as well as reducing the fluidity of the company's operations [8]. In contrast, high fleet availability enables a haulier to reduce the number of operational vehicles and the number of reserve vehicles [9]. Regarding the factors determining fleet availability in a public transport system, the following breakdown can be proposed, among others [10, 11]:Random external factors not attributable to the carrier, e.g., sudden weather conditions, road traffic collisions, and information misunderstandings due to contractors;
* Internal system factors relating to day-to-day operational management;
* Technical factors resulting from the reliability of vehicles. Delivering a guaranteed transport service in line with passenger expectations requires that the carrier continuously monitors the technical availability of the means of transport and infrastructure and that the reasons for insufficient availability are systematically analysed [12; 13]. Classifications of the factors affecting technical availability can also be presented as follows [14]:  
* Non-damageability of vehicles--resistance to the wear and tear of structural components and operational forcing, which determine the frequency of damage;
* Serviceability--effective maintenance management, the availability of spare parts, and the efficiency of service processes that minimise operational downtime;
* Reliability--the use of vehicle condition monitoring systems to plan maintenance work;
* Operating conditions--the intensity of use and the impact of the operating environment determine the wear and tear dynamics of vehicles and their availability for transport. Vehicle availability studies are widely reported in the literature. In relation to the topic of this thesis, this literature review mainly considers publications on the following:  
* The availability of vehicles for intervention tasks, e.g., police cars, military vehicles, and aircraft;
* The availability of urban public transport vehicles. This study highlights, among others, references [15; 16; 17; 18; 19]. In [19], to model the exploitation system of special vehicles, a semi-Markov process was used based on three exploitation states: use, use stoppage, and repair. Using a statistical sample of police cars as an example, an experimental study of the intensity of fleet use and the time of failure-free operation of vehicles was carried out, and it was shown that the studied transport system is characterised by a satisfactory stationary availability factor. The developmental possibilities of the presented modelling method are highlighted. Reference [15] presents an analysis of the impact of contractual categories of bus downtime due to maintenance and repair on the technical availability index. A retrospective study covering a period of 12 years of vehicle use was carried out using the example of a selected urban transport company. The share of each downtime category in the total vehicle downtime was analysed. The Spearman rank correlation coefficient was used for the analysis.