Provision: Infrastructure design and construction can incorporate reliability options. Increasing the physical capacity of infrastructure and improving supply-side reliability entails reducing the probability of an unexpected disruption in service. This can be achieved either through supplying extra capacity or improving the quality of existing capacity. Capacity enhancements are generally costly, time consuming and often politically difficult. Setting appropriate network standards and improving the robustness of infrastructure (for instance, durability of material) also influences reliability;
Information: Information may be used in different ways to improve reliability depending on whether a traveller has left the origin, whether a traveller can divert to another route, or if the traveller cannot divert but can reduce the ripple effect (consequences). Different tools exist for delivering information to users enabling them to mitigate the adverse effects of poor reliability. This can be a cost-effective way to reduce both unreliability and the impacts of traffic incidents on subsequent business and personal schedules.
Management: Better utilisation of existing capacity can facilitate reliability, just as poor management can increase unreliability. Infrastructure managers can improve reliability through better incident management and appropriate scheduling and publicising of maintenance work. The core management skills can be supplemented by pro-active network oversight.
Pricing: Charging directly for reliability can be used to achieve more efficient levels of reliability. Charging for the use of transport networks, or portions thereof, is becoming a more common method of managing traffic demand, and consequently traffic flow and network reliability. However, it is often difficult to provide different levels of reliability according to the value different users place on reliability, and equally difficult to extract different charges for differential performance.
A key policy challenge is to create incentive structures that encourage selection of the most cost-effective reliability option – the option that delivers a given level of reliability improvement for the lowest cost. The objective is to ensure that option is chosen ahead of the less effective options, regardless of whether the responsibility for adopting the option lies with the network provider or the network user. Indeed, reliability improvements can be delivered by both users and network providers. It should not be presumed that the infrastructure (or service) provider/government always has to be the source of reliability enhancements. The low-hanging fruit of cost-effective reliability improvements may come from network users.
A cost-benefit assessment (CBA) framework provides consistency in assessing the societal pros and cons of policy interventions in terms of their positive, or negative, effects on reliability. Incorporating reliability into CBA encourages proper consideration of options for delivering appropriate levels of reliability. Projects designed to deliver congestion reductions are sometimes credited with generating reliability benefits. However, standard appraisals fail to unbundle improved reliability (reductions in travel time variability) from the benefits due to the reductions in average travel time. This omission removes the factual basis for arguing that a project really does improve reliability.
Examples from current practices show that it is possible to take into account reliability in the CBA. These approaches provide a foundation for explicitly incorporating reliability benefits into investment appraisals and, consequently, policy frameworks. Incorporating reliability into CBA requires, in principle, three sets of data:
Existing travel time reliability, defined in minutes;
Anticipated reliability level, in minutes, after a change in policy or an investment;
Monetary values of reliability, disaggregated at the appropriate level.