Road Diets and Vehicle Positioning: A Before-and-After Case Study of Retrofitted Cycleways in Christchurch, New Zealand

The New Zealand (NZ) government has promoted road diet programs to improve the quality and quantity of bicycle infrastructure. Numerous cycleways have been retrofitted onto existing roadways as the public good generally outweighs the cost. This paper examines vehicle positioning changes when retrofitting separated cycleways onto existing roads in Christchurch, NZ. Two reconstructed roads were selected for this study. An Internet of Things (IoT) prototype was used to collect vehicle lateral positioning before and after the reconstruction projects. Although retrofitting cycleways onto existing roads brings several well-researched benefits for cyclists and society, the results from this study showed that as vehicle lanes became narrower to accommodate the new facilities, it presents new challenges for motorists to navigate, with very high centerline encroachment rates. Whereas the separated cycleway effectively prevented vehicle encroachment on cycleways and increased cyclist safety, the results showed that a road diet can significantly narrow the vehicle wheel paths. This effect has traditionally not been accounted for when implementing cycleways on existing roads in NZ and its impact on aspects of pavement maintenance needs to be further investigated. The results also showed that chip-seal contractors should recalibrate the variable bitumen sprayer to accommodate the new location and narrower wheel paths after a road diet to improve maintenance practices. These findings provide valuable insights for planning. Future research in this area could be aided by IoT-based approaches, as demonstrated by this case study.