Built environment characteristics and driving speed in 30 km/h zones: a Dutch national analysis

Road authorities are systematically expanding 30 km/h zones to enhance safety. This requires understanding how built environment characteristics are associated with driving speeds, but only a few studies, typically based on small samples, focus on 30 km/h streets. Using a spatial error model, this study examines the relationship between built environment factors and 85th percentile speeds on 47,000 km of Dutch 30 km/h streets (N=159.000). Driving speed and traffic volume data were estimated using floating car data, while built environment characteristics were collected from public sources. The results show that higher driving speeds are associated with greater traffic volumes, longer street lengths, closed pavement, separated bicycle tracks, visually marked bicycle lanes, and longer road sections. Features linked to lower driving speeds include curves, speed humps, raised intersections, exit constructions at zone entrances, narrower carriageways, roadside parking, nearby premises, and higher address densities. Furthermore, the identified interaction effects show that measures like speed humps and raised intersections have greater impacts in high-speed environments (i.e. long and busy streets with closed pavement) but limited effects in low-speed settings. These findings emphasize the need to consider combinations of road design elements and their context-dependent effects to understand driving speed on 30 km/h streets. Out study provides valuable insights into the effectiveness of speed-reduction measures, offering guidance for interventions targeting streets with excessive speeds.