The connectivity reliability of public transport depends on a number of factors, including public transport routes, the connections between them, their frequency, their availability, and the availability of public transport and infrastructure. A shortest path algorithm is used to find up to "k" paths connecting each Origin-Destination pair in space-time, taking into account the schedules and a constraint on the maximum tolerable waiting time. For each path, four reliability indicators are proposed, as well as an approachability indicator, related to the level of transport supply. Thanks to two sets of equations, these indicators are also computed on the origin-destination and network levels. This enables fleet managers to evaluate and compare strategies for improving the connectivity reliability and the transport supply, such as increasing the number of public transport routes, reducing route length or increasing frequency. From an application on the bus network of a city in Brittany in France, we show how to understand and use these indicators.