Browsing by Author "Saarsalmi, Perttu"

Increasing shopping distances caused by structural change of the grocery networks and society's way towards a 24-hour rhythm set new challenges for the groceries' spatio-temporal accessibility in Helsinki region. Despite these challenges, in the previous studies the physical accessibility of groceries has been measured inadequately without taking into account different transport modes, realistic travel times or temporal aspects. The aim of this study was 1) to understand how the spatial patterns of accessibility of the groceries vary taken into account different transport modes and times of the day, 2) locate areas of in/sufficient accessibility based on realistic travel times and how people are located within these areas, 3) measure how accessibility differs between the municipalities of Helsinki region and 4) test if public transport could compete with a car when traveling to the nearest store. The accessibility of the groceries was measured by calculating travel times from inhabited statistical grid cells to the nearest grocery by car, public transport and walking at 17:00, 22:00 and 1:00.The travel time calculations by car were based on a specific dataset MetropAccess-Digiroad which is modified from the original Digiroad by setting impedances for different kinds of crossroads. The effect of rush hour and whole travel change, including walking and searching for a parking lot, were also taken into account in this study. Travel times of public transport and walking were calculated with MetropAccess-Reititin tool which calculates realistic travel times based on OpenStreetMap and timetable information of public transport. In all calculations the opening hours of the stores were also taken into account. Several visualizations were made based on travel times: 1) interpolated travel time surfaces, 2) service gap maps showing the amounts of people living in the areas of low access, and 3) separation maps representing the differences of public transport and car accessibility. Also graphs showing the amount of people who can access the stores within a given time-budget were made, as well as graphs representing the average travel times to the nearest grocery in the municipalities of Helsinki Region. The results showed that modes of transport and times of the day affect significantly to groceries' accessibility. At 17:00 and 22:00 accessibility was good almost in all densely inhabited areas because of the dense transportation connections and comprehensive grocery network. In the night time accessibility was much lower especially by public transport and walking because of the sparse grocery network and insufficient public transport connections. Public transport and walking were able to compete with car mainly in Helsinki at 17:00 and 22:00. In general travel times to the nearest grocery were shortest in Helsinki and longest in Espoo and Kauniainen. During night-time the travel times were longest in Vantaa. Despite some questions related to data and methods, the results gave a good image of the spatio-temporal patterns of the accessibility of the groceries in Helsinki region. The travel time calculation methods and spatio-temporal analysis were unique compared to other accessibility studies in Finland and abroad. The study was also first in which the accessibility of grocery trade in Helsinki region was measured by taking into account time and realistic travel times of different transport modes.