How much of the variation in transit mode share is attributable to accessibility is not well understood, despite its significant policy implications. It is hypothesized that better transit accessibility leads to higher transit mode share. This paper explains block-group level transit mode share using transit accessibility in a logistic model for 48 major US metropolitan areas. Transit accessibility alone explains much of the variation in transit mode share for all 48 regions despite their geographical differences (adjusted R2 0.61, potential accessibility); models for individual cities have stable and interpretable parameters for transit accessibility. The models better explain mode share in cities with higher person weighted transit accessibility and larger populations; an adjusted R2 of 0.76 is achieved for New York City with transit accessibility as the only explanatory variable. Additional automobile accessibility and income variables modestly improve model fit. Time-decay functions fitted to accessibility measures better explain mode choice than the isochrone accessibility, and suggest the catchment area affecting transit mode choice to be within 35 minutes. This work contributes to the understanding of transit mode share by solidifying its link with accessibility, which is determined by the structure of the transport network and land development.
Transit accessibility to jobs (the ease of reaching work opportunities with public transport) affects both residential location and commute mode choice, resulting in gradations of residential land use intensity and transit (public transport) patronage. We propose a scaling model explaining much of the variation in transit use (transit commuters per km2) and residential land use intensity with transit accessibility. We find locations with high transit accessibility consistently have more riders and higher residential density; transit systems that provide greater accessibility and with a larger base for patronage have proportionally more ridership increase per unit of accessibility. All 48 metropolitan statistical areas (MSAs) in our sample have a scaling factor less than 1, so a 1% increase in access to jobs produces less than 1% increase in transit riders; the largest cities have higher scaling factors than smaller cities, indicating returns to scale. The models, derived from a new database of transit accessibility measured for every minute of the peak period over 11 million US census-blocks, and estimated for 48 major cities (MSAs) across the United States, find that jobs within 45 minutes most affect transit rider density. The findings support that transit investment should focus on mature, well-developed regions.
I was interviewed about our Access Across Australia report by Jane Slack-Smith. It was a really good interview and got into the connections between access and real estate prices. The interview is posted to Facebook, for those of you who use the platform:
Accessibility – the ease of reaching valued opportunities such as jobs, workers and shops – is the whole reason cities exist. There is no reason to locate anywhere but to be near things, far from things, or to possess things. Access measures this.
Locations with better accessibility to urban opportunities generally have higher development density and more expensive real estate. This is because places with higher accessibility are more productive, so their workers earn higher wages. And modes of transport that reach more opportunities – that is, provide access to places where people work, live, shop, and more – tend to have higher market share.
Our new report, Access Across Australia, for the first time generates a set of consistent maps and graphs of 30-minute access to jobs and workers by each transport mode for each of the eight capital cities. This covers around 70% of the nation’s resident workers and employment opportunities.
The full report compares 10-minute to 60-minute accessibility to both employment locations and to workers’ homes by four modes of transport – car, public transport, walking, and cycling – for each city. It also reports the overall job-worker balance, comparing how many workplaces can be reached to how many competing workers want to reach those same workplaces.
The accessibility measures take into account the effects on travel times of traffic congestion and the walking and transfer elements of the public transport mode.
Accessibility captures the combined effect of land use and transport infrastructure. The faster and more direct the network, the higher the access. The more opportunities (people and places) that can be reached, the higher the accessibility.
This value varies across and between regions. For this article, we show this in maps for Sydney – the full report has maps for all four transport modes, for both jobs and labour (resident workers), for all eight cities. In the table, city-level accessibility numbers are reported as a metropolitan average, weighted by the number of people who experience that accessibility (population-weighted accessibility), to best represent the experience of the working population.
The rankings in the table are discussed below for each mode.
Cars have higher accessibility than public transport, walking, or cycling. Perth has the greatest number of jobs and workers reachable by car within 30 minutes.
At time thresholds of 40 minutes and longer, residents of Sydney and Melbourne have higher accessibility than other cities. During the morning peak period, Melbourne has moderately better car accessibility than Sydney, despite Sydney being larger and having more opportunities overall. This indicates that roads in Melbourne are faster than those in Sydney.
Public transport accessibility incorporates time to reach transit stops and station on foot, and equals the minimum of walking and transit times between an origin and destination. It remains at a significant disadvantage compared to car travel, reaching between 12% and 18% of the urban opportunities accessible by car under a 30-minute threshold.
Public transport accessibility tends to be high in city centres and low in other places. The disparity with cars peaks at 20-30 minutes’ travel time.
Sydney and Melbourne have the best public transport accessibility among Australian cities, followed by Perth and Brisbane. It could be higher still with better-located station entrances and exits.
This report identifies cycling as a viable option for improving accessibility. Assuming cyclists are willing to ride on the street, people cycling can reach about twice as many jobs as people on public transport within 30 minutes in all eight Australian cities, and around one-third of job opportunities reachable by car (except for Perth, which is 16%). Sydney and Melbourne have the highest cycling accessibility.
Of course, it should be recognised that many potential bicyclists are extremely uncomfortable riding in traffic. Their accessibility on a more limited network of residential streets and protected bike lanes would be much reduced.
People walking cannot travel as fast as those on other modes, particularly over longer distances, where public transport and cars can travel at much higher speeds. Not surprisingly, walking has the lowest accessibility of all four modes. The presence and timing of traffic signals that give priority to cars significantly reduces walking accessibility.
Walking accessibility is closely related to urban density. City centres, especially those in larger and denser cities, tend to have better walking accessibility.
Among the eight major Australian cities, Sydney and Melbourne have the best walking accessibility. Hobart and Darwin have the lowest.
The job-worker balance of a place is measured dynamically as the ratio of jobs and resident workers reachable within 30 minutes. City centres have superior accessibility to both jobs and workers, and less pronounced advantage in car accessibility compared to other modes. Higher jobs-to-workers accessibility ratios in city centres show that, in general, jobs are distributed closer to and better connected with city centres than residential locations.
This research gives us a baseline accessibility measurement using the best available data for 2018. Repeating this analysis over time will enable long-run tracking of accessibility as a performance measure.
This will enable us to answer questions such as: is accessibility by a particular transport mode rising or falling? Is that due to congestion, network contraction, new infrastructure, or changes in residential or employment density? Are policies working to expand accessibility for the population as a whole, and for areas within cities? Which investments give the most accessibility “bang for the buck”?
Some of the results are surprising – in particular, the observation that the speed of Perth’s freeway and street network more than compensates for more limited scale in producing 30-minute car accessibility.
But this result is just an indicator of broader accessibility, which includes additional relevant opportunities, more times of day and more information than is presently at hand. This is likely to become more widely available in an era of big data if governments choose to actually implement the open data claims they advertise.
When we talk about access as a value that should guide transport policy, we need to address access for whom, not just access to where by what mode. In the auto-dependent US, the mode that offers the most access in most places currently is the car. Yet cars are expensive, and many people struggle with basic access (and mobility) simply because they can’t afford it. Transport is the second largest spending category for US households, behind only housing. This is the case even as transport is heavily subsidized, regardless of mode.1 As discussed in Subsidy,2 the general approach is to spread whatever help is offered thinly across infrastructure capital investment. This does little to help those with the least.
This article, by Somwrita Sarkar, Hao Wu, and David Levinson first appeared in The Conversation.
The Greater Sydney Commission has proposed a 40-year vision of a metropolitan region formed of three “cities”: the Eastern “Harbour” City, the Central “River” City, and the Western “Parkland” City. The plan aims to create 30-minute cities, where the community has access to jobs and services in three largely self-contained but connected regions. Thus, Sydney would be polycentric.
A polycentric city has multiple centres of employment, economic or social activity. Local labour markets and residential zones minimise long commutes, create a sense of place and neighbourhood, and strengthen economic agglomeration as companies, services and industries benefit from being close to one another.
However, it is still unclear whether Sydney is actually moving towards such a structure. In our recent work, we developed new ways of measuring polycentricity. We applied these to Journey to Work data from the 2016 Census to test how consistent the current centricity patterns of Greater Sydney are with the proposed plan.
How do you measure polycentricity?
Traditionally, employment densities are used as a measure of polycentricity. If the density of jobs in a location is higher than the average density for the entire region, then it is a centre.
However, this simple measure misses a key notion that makes cities what they are: network flows and spatial interactions. People “flow” from one place to another. Employment centres “attract” flows, and residential areas “produce” flows. Thus, a city is a collection of locations that interact dynamically, connected by daily commuting flows.
We proposed a set of new metrics to capture this idea of flows. We defined the net inflow of people to a location as the total number coming to this location to work minus the total number going from this location to work elsewhere. If the net inflows are positive, this place is a centre.
The chart below illustrates the idea. The base arc on the circle shows the number of people “flowing” out of a location to another location. The connecting arcs are coloured black if the net inflows into the focus regions (a), (b) or (c) are positive.
Sydney CBD clearly emerges as a global centre for the whole region. Parramatta is a regional centre. Other locations such as the Eastern Suburbs are not centres at all.
The net inflow to a location can be divided by the total number of trips in the system, so inflow values are scaled from 0 to 1 using a standard statistical procedure. The higher the value, the higher the centre’s rank in the urban system. Here, a score of 1 means the centre is an absolute: all the trips in the system are a net inflow into the centre.
This gives us a trip-based centricity measure. And based on the area of the location, we can calculate a density-based centricity measure.
The maps below show trip-and-density-based measures – (a) and (b) respectively – for Greater Sydney at the Statistical Area Level 2 (representing a community that interacts together socially and economically).
Note the dominant role of the Sydney CBD. The other centres emerge as weak centres. Also, many of the second-order centres are very close to the CBD.
The concept of accessibility
Counting the net inflow into a location may provide us with information about general centricity. However, it still does not tell us how easy or difficult it is for people to actually get to jobs. This brings us to the idea of accessibility.
Walter Hansen defined accessibility as “the spatial distribution of activities about a point, adjusted for the ability and the desire of people … to overcome spatial separation”. More practically speaking, a location is accessible if it can be reached within a set time (say 30 minutes) from another location.
We counted the net accessibility of a location by counting the number of jobs minus the number of workers (labour) that could be accessed from a particular location (SA2) in Sydney within 30 minutes. We counted travel time both by car and by public transport during a usual weekday peak hour (Wednesday 8am). Similar to the trip and density measures, accessibility centricities can also be scaled as values between 0 and 1. This allows us to compare across the four measures.
In the maps above, (c) and (d) show the transit and auto-based accessibility centricities based on accessibility for public transport and vehicles. Sydney CBD is highly accessible. The second-order centres show much weaker accessibility.
Takeaways for urban policy and the three-cities plan
The chart below shows the top-ranked centre, Sydney CBD (Level 1 centre), and the lower-ranked subcentres (Levels 2 and 3) emerging from our analysis.
Accessibility planning should guide the design of a polycentric city
The design of polycentric Sydney should be guided by accessibility, the locations of jobs and homes, and subregional labour market organisation.
In short, the region should give priority to making jobs accessible by locating new jobs in emerging centres, instead of a mobility-focused system that takes people to jobs.
Reduce spatial mismatches between jobs and homes
Our results show that Sydney, paradoxically, remains strongly monocentric and strongly dispersed at the same time. The Sydney CBD accounts for 15% of jobs in the region, with the remaining 85% of jobs scattered around in weaker second-order centres and non-centres. Positive correlations exist between percentage of employed workers, trip-based centricity and the subcentre ranks.
But we see significant disparities between these ranks and accessibility centricities. This shows the spatial mismatches for commute lengths in the system.
A subcentre with high trip-centricity, employing a high percentage of workers, but relatively lower auto- and transit-based accessibility centricity, implies that even though a significant percentage of the population comes to this location to work, access to jobs at this centre within 30 minutes is low.
A policy response would be to increase the accessibility of jobs from this location, as it already serves as a centre. This situation is particularly clear in the cases of Parramatta-Rosehill and Macquarie Park-Marsfield. Penrith and Liverpool too have extremely weak accessibility centricity.
Polycentric cities should promote spatial justice
As cities grow in size, commute lengths increase if the labour market for the entire metropolitan region is integrated. Commute lengths will stabilise if a city has a clear polycentric or modular structure.
Our results show it’s increasingly important for larger cities to introduce a framework of subregional labour markets as part of the polycentricity agenda. Enabling shorter commutes for workers will improve spatial equity as well as efficiencies.
Train riders have to get to stations somehow. This is often referred to as the “first mile” or “last mile” problem. There are many technical solutions to help travellers get from home to the station and back, ranging from cars to electronic scooters, but most people use a much older technology, their feet, to get from A to B. What is seldom considered is access to the train platform itself.
Stations are not points but places. They occupy a large area. A person walking at average speed takes about two minutes to walk from one end of a full-length eight-car train to the other.
Often platforms have a single access point on one side of the station, which makes it more difficult for people on the other side of the station to get to the platform. Passengers may need to almost circumnavigate the station to get to the platform. At an average walking speed, the extra distance they must backtrack adds up to six minutes per trip each way, our research has found.
Imagine being so unlucky to have an extra 12 minutes of travel time every day if you take the train. You might be tempted to drive instead.
The table below shows the extra travel time in minutes depending on platform locations and access points for a traveller’s origin and destination. The average time for such a one-sided configuration of train stations is 3.25 minutes each way.
Table 1: Additional Travel Time Depending on Origin and Destination Residence and Workplace Location vis-a-vis Platform Location.
While this example is hypothetical, it is drawn from experience in Sydney, where 44 of 178 train stations have only a single side entrance.
So what impact will a second entrance have?
We examined those stations and access to their platforms: how many people lived within 5, 10 and 15 minutes of the station platform, considering actual entrance location, and how many jobs were within 5, 10 and 15 minutes of the platform. Using existing ridership data from Opal cards, we estimated a model that related the passenger entry and exit flows at each station to that station’s accessibility.
We sketched a second entrance at those 44 stations and measured accessibility again. It’s now higher, as having two entrances instead of one means more people can reach the platform in the same time. We then estimated the increase in ridership from the model due to the improved accessibility, assuming no change in population or employment.
Over all 44 stations, total morning peak period entries increased by 5%. But some stations benefit a lot, and others not at all, so prioritisation of investments matters.
It will be no surprise to locals that Erskineville station comes out on top with a nearly 35% increase. While many of the new apartment-dwelling residents west of the station make the extra hike every day, even more would catch the train if there were a convenient entrance.
Other top 10 stations include: Bankstown, Newtown, Villawood, Redfern, Burwood, Sydneham, Caringbah, Meadowbank and Penshurst. Planning is already under way to improve Redfern station.
While this result considers existing development, adding a second entrance can make new transit-oriented development that much more valuable. This is because it will likely increase activity on the previously less accessible side of the station, as the example of Erskineville shows below.
Other considerations include accessibility for people who cannot use staircases, as many of the stations are older and will require lifts. The prospects of park-and-ride lots, the costs of construction, the presence of nearby stations, and site feasibility also play into final decisions.
The automobile has been pitched as a machine for freedom. But you travel caged inside a small metal box, strapped to your chair, while your life is being threatened randomly by high speed two-ton projectiles, forced to keep eyes focused on the road and obliged to place hands at the 10 and 2 o’clock positions on the wheel, with your foot constrained to a small area on the floor. This doesn’t sound like freedom to me.
If you choose to enter a freeway, you are not even permitted to leave your car til you exit the road.
On streets, your behavior is governed by inanimate traffic lights, signs, and paint, which are violated at penalty of automatically generated fine or imprisonment.
This is all self-imposed, so it is more like committing yourself to an institution, the automobility asylum, perhaps, than prison which is imposed by others.
An alternative view is that freedom is not ensconced in a machine but in a way you can interact with the world. If you can, at your whim, when you want to, do what you want, engage in the activities you want, without fearing for your life, that is closer to freedom.
Jarrett Walker argues frequency is freedom. This is closer to the truth. While on a bus or train I am still caged in a metal box, it is a larger box, I am not strapped in, and I am much safer. I am also now free to do something with my time while in motion, not constrained to monitor the road.
Freedom from car ownership, freedom from the obligation of driving, and freedom from negative externalities borne by the community at large are how we should reframe transport and land use goals. What can we do to give people those freedoms?