Transport Accessibility Analysis Using GIS: Assessing Sustainable Transport in London
2. Measuring Transport Costs and Accessibility
3. Implementation of GIS-Based Model
- First, the spatial geography of the model is defined in terms of zonal geography and the spatial boundary of analysis (for example for the London case study presented below, these are UK Census Area Statistics Wards, i.e., zones on which 2001 UK census outputs are reported).
- Build M transport networks:
- Analyze, and clean if necessary, the data to ensure the correct topological structure for creation of a spatial network model.
- Build spatial networks within GIS software.
- Calculate the length of each network link from geometry.
- Multiply each network link length by the relevant travel speed to obtain the travel time for each link.
- For N units of spatial geography, create an N x N matrix of generalized costs for each of the M transport modes (similar to the approach outlined by Benenson et al. ):
- Calculate the location of the centroid and use it to define the Origin, and Destination of zone i.
- Calculate access distance, do, and associated travel time from centroid to nearest network access location (private and cycling modes), or boarding point (public transport modes) (Figure 2)
- Calculate access distance, dd, and associated travel time from destination station or stop (public transport) or road access location (private and cycling modes) (alighting point) to the centroid of the destination zone (Figure 2).
- Eliminate nonsensical journeys (e.g., where nearest station is shared between the origin and destination) and return a no-data value.
- Add on other costs, including non-monetary and monetary components in Equations (4a)–(4c) such as fuel or perception weights, converted to time.
- Sum all journey components to calculate the generalized cost of travel, Cij, between two zones.
- For situations where i = j and the preceding steps calculate Cij = 0 then assume that in line with the approach used by Feldman et al. .
- Use computed generalized costs to determine accessibility to destinations of interest (e.g., employment locations) and determine the proportion of employment which is accessible by a given mode in a given cost of travel.
|T2025 Scenario||Road||Bus||Rail||Light Rail|
High Speed 1
Heathrow Express to Terminal 5
|Heathrow Terminal 5 extension|
|Low||Thames Gateway Bridge||20% increase in bus supply (and thus frequency)||Reduce journey time by 4.5%||DLR extensions, Greenwich and East London transit systems|
|High||Silvertown Link Bridge|
National Road User-charging scheme
|40% increase in bus supply.||Crossrail 2, East London line extension (Overground).||Tramlink extensions, DLR extension to Dagenham Dock|
|Parameter||Description||Value Used in Analysis|
|A||Time take to access a given transport network mode from a place of residence. This uses do and dd which are the distance from the transport mode to the zone centroid (Figure 2).||Private transport modes: 3 min - the maximum access distance in Greater London is 800 m (in the Hillingdon ward in western Outer London), with the mean distance being 130 m.
Public transport modes: Distance from zone centroid to station, with a walking speed of 6 km/h
|Vwk||Weight applied to the walking component of a journey to reflect the increased perceived cost of walking compared to other transport modes (applied to do and dd).||1.6 from WEBTAG |
|T||The in-vehicle travel time is computed by multiplying the network distance by an average speed. This is the time taken to travel distance dn.||Computed from network analysis described in Section 2.
Car: defined by 2006 London Travel Report Table 3.2.1, which gives the average journey speed for three traffic zones; central, inner and outer London .
Heavy rail: 40 km/h
Light rail: 30 km/h
Bus: times supplied in network data
|W||Waiting time is calculated as half the average morning peak service frequency for public transport modes.||Rail: 7.5 min
Light rail: 3 min
Bus: 3 min
|Vwt||Weight applied to any waiting time, reflecting the perceived cost of waiting compared to travelling, and a dislike of waiting for infrequent services.||2.6 from WEBTAG |
|D||Distance travelled (km) traversing the least cost path from origin to destination, and is equivalent to dn (Figure 2).||Computed from network analysis.|
|VOC||Vehicle Operating Cost is the sum of both fuel, VOCf, and non-fuel, VOCnf, costs (which capture maintenance and depreciation costs).||Fuel costs,|
where Fm is a vector of the vehicle mix and their fuel efficiency and Fp is a vector of fuel prices.
Non-fuel operating costs can be computed by the following:
where V = average velocity in km/h; a1 = 4.069; b1 = 111.391.
|VOT||Value of Time.||1 hour = £5.04 from WEBTAG |
|occ||Average number of occupants in a private vehicle.||1.16 people per vehicle |
|PC||Other private transport costs. Information on parking costs and policies was incomplete for London so have not been included in this analysis. However, the London Congestion Charge, levied on vehicles entering the center of the city, has been included.||Congestion Charge of £8 (2008 charge) levied on each journey into the charging zone. 90% discount for residents of the zone travelling out for work .|
|F||The fare paid for a given origin-destination route varies according to the time of day and whether the individual has a season ticket, travel card, or uses an “Oyster Card”. An average rail and light rail cost is reported in the London Travel Report (TfL, 2006). Flat bus fares £2, or £1 with an “Oyster Card”. However, 85% of journeys (TfL, 2007) use an Oyster Card so this was used for all journeys in this analysis.||Heavy and light rail: £0.18/km
Bus: £1 flat fare
|VTopo||It is assumed that cycling journeys incur a lower cost on flatter terrain than on more undulating terrain. In this paper, a modified version of Naismith’s Rule is used, where each unit of vertical change adds 1/8th of a unit of horizontal distance to the journey.||1/8 * (Zmax − Zmin) for a given road link, where Zmax and Zmin are the maximum and minimum elevations at either end of the link.|
|VSafe||One of the largest disincentives to cycling in urban areas is the issue of safety on the road network (especially in London, where cycling infrastructure is patchy and a number of cyclists are killed every year). A weight is therefore applied based on the class of road being traversed. These are assumed weights but can be simply altered to reflect further research on perceptions of risk.||A-Roads, B-Roads: 1.5 times base travel time
Minor roads: 1.2
Residential streets and pedestrian paths: 1.1
Cycle lanes: 1
Adapted from the methodology employed in the CycleStreet route planner 
4. Results and Discussion of London Accessibility Study
4.1. Testing New Infrastructure Investment
4.2. Accessibility to Employment within London
4.3. Global Accessibility Improvements
|Bus||Light Rail||Rail||Road: With CC||Road: No CC|
|Low investment||9063 (−1.4%)||13,605 (−1.9%)||9575 (−2.0%)||8520 (−0.3%)||5997 (−0.5%)|
|High investment||8285 (−9.9%)||13,325 (−3.9%)||9490 (−2.8%)||8698 (+1.7%)||6176 (−2.5%)|
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Ford, A.C.; Barr, S.L.; Dawson, R.J.; James, P. Transport Accessibility Analysis Using GIS: Assessing Sustainable Transport in London. ISPRS Int. J. Geo-Inf. 2015, 4, 124-149. https://doi.org/10.3390/ijgi4010124
Ford AC, Barr SL, Dawson RJ, James P. Transport Accessibility Analysis Using GIS: Assessing Sustainable Transport in London. ISPRS International Journal of Geo-Information. 2015; 4(1):124-149. https://doi.org/10.3390/ijgi4010124Chicago/Turabian Style
Ford, Alistair C., Stuart L. Barr, Richard J. Dawson, and Philip James. 2015. "Transport Accessibility Analysis Using GIS: Assessing Sustainable Transport in London" ISPRS International Journal of Geo-Information 4, no. 1: 124-149. https://doi.org/10.3390/ijgi4010124