reistijdindex

Reistijdindex, often translated as travel‑time index, is a traffic‑performance indicator used primarily in the Netherlands to assess the reliability and efficiency of road routes. It expresses the ratio between the actual travel time experienced by drivers and the travel time under free‑flow conditions, which are measured during periods of minimal congestion. A value of 1.0 indicates that travel proceeds at the optimal speed, while values above 1.0 reflect increasing delays; for example, an index of 1.3 means that trips take 30 % longer than under free‑flow conditions.

The index is calculated from continuous traffic‑monitoring data collected by loop detectors, probe vehicles, or automatic number‑plate recognition systems. For a given period—typically a month—the average observed travel time for a specific road segment is divided by the corresponding free‑flow travel time, which is derived from historical observations during off‑peak hours. Results are often presented as daily or hourly series to highlight temporal patterns such as rush‑hour peaks.

Reistijdindex is employed by transport authorities, urban planners, and navigation service providers. It supports congestion‑management strategies, informs infrastructure investment decisions, and underpins real‑time traveler information systems that suggest alternative routes. The metric also appears in the Dutch National Travel Time Index (NTTI), a composite measure that aggregates indices from multiple corridors.

Critics note that the index does not capture the variability of travel times, leading to potential misinterpretation of reliability. Complementary measures such as the Travel Time Reliability Index (TTRI) and the Planning Time Index are therefore used alongside the reistijdindex to provide a more comprehensive view of traffic performance.