Accessibility studies implemented by Helsinki Region Transport

The future urban structure of a city is highly based on its current structure. Therefore it is necessary to study the impacts of the current structure in relation to how people move in the city. In accessibility studies (SAVU) completed in Helsinki region, accessibility was analysed from the point of view of sustainable mobility, i.e. walking, cycling and use of public transport by people living in the region. The aim was to show the most potential areas for land use development from the point of view of supporting sustainable mobility.

The study was implemented by Helsinki Region Transport. The accessibility maps created have served, for example, the preparation of the Letter of Intent on Land Use, Housing and Transport (MAL) for Helsinki region. In future, they will be utilised e.g. for the purposes of monitoring the implementation of the current Helsinki Region Transport System Plan (HLJ) 2011 and the preparation of next plan in 2015.

The accessibility studies conducted describe the regional accessibility of each 250 x 250 meter square in the Helsinki region area grid. The overall accessibility of each square relative to all other squares was modeled using a purpose-built mathematical model (RUUTI2), which takes into account not only the mode of transport used but also the proximity of different functions, as well as the transport options provided by the transport system for trips made for different purposes between the squares.

The number of trip purposes studied was ten, based on different locations, and different distances, using different modes of transport, were calculated on the basis of an Extensive Traffic Survey carried out in 2007-2008. Descriptions of the transport network as it currently stands, as well as in 2020 and 2035 served as starting points for the descriptions of the level of service for the transport system and land use in different squares.

After determining the accessibility of each square on different types of trips made by sustainable modes of transport, the accessibility figures measured on different scales were calculated and the overall accessibility of each square was determined by combining the trip group-specific accessibility figures of the square weighted by the corresponding number of journeys. Next, the squares are arranged in order of magnitude on the basis of the overall accessibility, and divided into seven categories so that each category has a predetermined number of residents. Subsequently, the squares in each category are colored with the same color to form continuous areas or so called accessibility zones on the map. 

When different future land use and transport system scenarios are explored, the squares start to move from one accessibility category to another and consequently, the boundaries of the accessibility zones begin to change. In this way, it is possible to obtain a visual image of the impacts of these changes in the accessibility of different areas.

The results show that there is significant variation between different zones in regional travel, and the zones can be verbally described according to the way in which the residents of each zone typically travel. For example, in zone I (inner city, typical modes of transport are walking, cycling or very frequent direct public transport services) residents nowadays make 3/4 of their trips by sustainable modes of transport thus producing about one kilo of greenhouse gas emissions per day. In zones V (outskirts of the city and major population centers in the country side, trips are typically made by car, some of the trips by public transport) and VII, (scattered settlement, trips typically made by car) residents make only some 1/3 and correspondingly 1/5 of their trips by sustainable modes of transport producing 3 and 5 times as much greenhouse gas emissions than in zone I.

Photo: HSL/Lauri Eriksson