Quoting from a discussion about Melksham to Bath and the Bradford North Curve.
This talk of catchments set me wondering, because it doesn't seem right to assume that buses and train/tram stations have the same catchment size.
A study for Bournemouth supports this view, suggesting that whilst heavy rail or metro systems might have a catchment radius of 800m to 1.2km, for tram systems it is nearer 400m to 600m. Grahame's 250m radius may well be right for buses. In essence, the catchment increases in proportion to the quality (in all its aspects) of the service.
And then again ... how about when two access points are both within easy distance of an individual's staring point / front gate / workplace entrance / caravan? Do the areas overlap? Do you allocate to the closest or the best served? Will people travel out from one access point and back to the other / how much of that gets involved with ticket acceptance, etc?
Comment is made about some local use made of Lelant Saltings, offering Lelant or the bus as alternatives. Perhaps this traffic which is within the catchment of both stations has gravitated to the Saltings because of the much better service and will revert to Lelant in the future? I am noting the extra calls at Lelant are lunchtime and school-end time.
Circles / distances from stations are in any case a very rough measure indeed. Some would go further. From David O'Connor and Oran Harrison at the Dublin Institute of Technology, School of Transport Engineering, Environment and Planning (
https://arrow.dit.ie/cgi/viewcontent.cgi?article=1013&context=beschspcon )
The Euclidean method of measuring a rail station’s catchment, a circle on a map, is widely discredited in most literature; the failure of it to allow for natural and manmade obstacles means a more detailed method is required for accurate results [14]. Landex and Hansen [14] recommend the Network Analyst approach of mapping the real walking routes along the street network to the station. They map the catchments for rail stations in Copenhagen using both methods to show how the Euclidean method’s inability to take rivers into consideration leads it to include areas with no actual access to the stations whereas the Network Analyst approach identifies these obstacles and makes the relevant changes to the catchment area.
The Euclidean method can often have a detour factor built into it e.g. even if people are willing to walk 1km the circle will have a 800m radius to take account of obstacles. Once again however Landex and Hansen [14] point out that a one size fits all detour factor is not useful because as the urban grain of areas differ so would the detour times. Ker and Ginn [3] point out that even in areas of high pedestrian permeability, e.g. inner city neighbourhoods, circular walking catchments still only reach 60% efficiency which drops as low as 10% in poorly connected, often outer suburban, areas.
Actual walking routes are rarely as direct as the Euclidean method assumes meaning that the actual catchment area is smaller than expected; if the actual walking route is a third longer than the Euclidean method uses then the actual catchment radius is 75% of the original assumption and the actual population could be 56% of that projected. Barton et al. [13] support the use of the Network Analyst approach to map the real routes travelled and as such better plan the location of public facilities including rail infrastructure.
I know what he means ... as I was drawing circles on maps on the thread I've broken this off from, I was wondering (on Staverton Station) where would the ststion entrance be - and where the access routes would run. And I'm aware of the 800 metre walk at Melksham to get to Foundry Close on the old goods yard, where fence panels block the direct line between (!) two pieces of Wiltshire Council land and the walk should be 50 metres.
Circles, or shapes, as drawn also have hard boundaries, but really they need to fade. Most people will walk two hundred metres from the station. Few will walk two miles. But what about 800 metres? A mile? 2km? And I'm going to suggest that walking distances vary depending on what you are walking to. From Melksham Station, I will walk 1500 metres (ish) home, but I wouldn't think about walking 350 metres to the nearest bus stop. But then if it's peeing down, would I walk the 1500 metres?
So - how should we define the catchment area around a public transport access point? How do we estimate abstraction of traffic from one access point by a proposed new one? How do we correlate market penetration of an access point based on the frequency and desired destiantion of the services that do or will call there?
