Reliability in transport is one of the topics on which one of the committees of the World Road Association (WRA) will be focussing intensively for the next four years. But what does reliability in transport actually mean and does it mean the same thing everywhere? We asked our expert, Prof. Dr. Christoph Walther, Head of Global Research at the PTV Group, who was named a member of the Road Transport System Economics and Social Development Committee in February 2016.
Compass: WRA is an organization that is supported by the governments of its member countries. The general objective of the World Road Association is to promote international cooperation in the field of roads and road transport. Expert teams examine different topics in committees for four years apiece. Christoph, you were named to one of the committees of the WRA at the suggestion of the German Ministry of Transport. Can you describe your work there for us, especially as it relates to the topic of reliability?
Christoph Walther: The committee mentioned above, which is composed of approximately 20 members, focuses on the one hand on the topic of reliability and on the other on ex-post analyses. Ex-post project evaluation is carried out in order to assess the impacts of a project and whether it achieved its original objectives. That is, whether travel times are shorter, how the noise pollution in an area has developed or the effect the project has had on road safety. This type of evaluation is performed for projects around the world. In some countries, ex-post analyses are required by law; this is not the case here in Germany.
Also extremely interesting is the topic of reliability of transport systems, because everybody is talking about reliability, but it is not at all easy to define because it affects the infrastructure in addition to the traffic flow, and not least because differences between industrialised and developing countries as well as between different climate zones must be formulated.
In a nutshell, reliable traffic and transport can be measured by determining how sharply the real travel time differs from the anticipated one. This is a topic that is not only interesting for us as private or business travellers, but also for the transport industry, where time truly is money. Therefore, reliability affects a multitude of areas and is also reflected in entirely new topics such as autonomous driving and urban logistics. And this is the case around the world – however with local accents.
Compass: In case of deviations, the first suspicion is that there are traffic jams.
Christoph Walther: This is an example that people like and mention often – but actually for unreliability. Whereby the morning traffic in which commuters regularly find themselves is reliable, to be precise about it. However, there are also early arrivals in the context of unreliability, whereby we perceive these as less unpleasant when travelling privately than delays.
Compass: And how can you record and assess reliability more precisely?
Christoph Walther: Overall, there are three approaches for quantifying reliability in the transport sector: The standard deviation of the travel time distribution, frequency and extent of the deviation from agreed-upon arrival times in schedule-bound systems, and finally buffer times for avoiding delays. The transport time is longer due to the buffer, but more certain.
Compass: I assume that for the assessment of reliability, there is a distinction between passenger and goods transport?
Christoph Walther: Correct. Here there are also very different requirements. In passenger transport, the travel time is the decisive factor which immediately determines the arrival time. In goods transport, the timely arrival at the target company’s ramp is decisive. That is to say, it is not absolutely relevant whether the actual transport is fast or slow. “Just in time” always relates to the arrival. There are extreme examples in the chemical industry, if during transport by train the train is used as a rolling warehouse for several days to avoid expensive intermediate storage at the producer or the recipient.
Compass: Can this definition or type of recording and assessment be applied internationally?
Christoph Walther: These very general approaches can serve only as a starting point in a worldwide discussion. Variations of travel times that would cause an overplanning of routes in Europe will be meaningless in countries with very long and uncertain transport routes. In the course of the work of the WRA, in the next cycle we will also organise an international workshop in order to formulate the various aspects of reliability in different economic, climatic and cultural environments and integrate these into assessment processes for infrastructure projects.