Shifting Trends From Mobility to Accessibility and Evaluation of Accessibility based
Measures – A Review and Comparative Case Study
Bincy Mariam Koshy, UIN – 663340959
The mobility – based perspective has been dominating the transportation world and is also
prominent among the general public. Common indicators based on this approach include
dollars wasted while waiting in traffic and Level of Service (USDOT). Transportat ion engineers,
planners and the public view ‘rapid movement’ as the ultimate success. However, this
perspective has its drawbacks – movement is not the desired outcome by people rather
interaction with people and places they want to engage with at destinat ions. Thus, speed is
not imperative and significant. Accessibility – based model includes measuring the level of
interaction with people and places; this implies that at lower speeds, high interactions are
possible in nearby destinations.
Accessibility is defined as the ‘potential of opportunities for interaction’ (Hansen) or the ‘ease
of reaching places’ (Cervero) while mobility is defined as the ‘ease of movement’. Accessibility
is used as an evaluation criterion and is a function of both land – use patt erns and
performance of transport systems. One predominantly useful feature of accessibility is its
ability to pinpoint areas or groups that are underprovided and hence influences plans and
sometimes only requires spatial reallocation of resources. But the debate on whether
accessibility or mobility should be the objective in transportation planning is still ongoing
despite many advantages of accessibility -based evaluation.
A shift from mobility to accessibility is crucial for improving transportation syste ms as it is the
primary criterion by which transportation policy is evaluated. The demand for transportation
is a derived demand – this demand is due to the need for people to reach destinations which
implies that people do not travel for the pleasure of m otion but to reach destinations and this
derived nature yields that accessibility is the service provided by mobility. Hence the shift
from mobility to accessibility is required to be consistent with the consensus that the demand
for transportation is deri ved and the ultimate goal is to reach destinations. This is why the
research on shifting to accessibility -based evaluations is crucial in the transportation world.
So far, the need for a shift from mobility to accessibility has been discussed and is yet t o be
discussed further in detail. Mobility, proximity and connectivity are different means of
attaining accessibility. But mobility and proximity exist in tension with one another and
therefore exert conflicting influences on accessibility as they have a n egative relationship.
Therefore, mobility and proximity are means of attaining an end, accessibility, which is why it
is essential to evaluate the components, mobility and proximity as it directly influences
In order to evaluate accessibili ty, two metropolitan regions, namely Washington DC and San
Francisco are chosen. The effects of mobility and proximity are analysed separately to
understand accessibility -based measures. While San Francisco has greater accessibility due to
high speed roadw ays, central Washington has closer proximity advantages. This comparative
study will also help us better understand why the shift from mobility to accessibility is
important and strategies to enhance accessibility in the context will be discussed.
Summary of Work
This pa per will help us investigate few questions:
• Q) What caused the shift from mobility to accessibility based on impacts of
mobility -based evaluations? (Done)
• Q) What are the obstacles to accessibility -based evaluations and what approaches
have been adopted to overc ome it? (In the process of completion)
• Q) What are the effects of proximity and mobility on acce ssibility in different
contexts? (To be done)
So far a detailed study has been conducted on the reason for shift from mobility to
accessibility which helps answer the first question in this paper. Follow ing is a summary of the
Importance and Reaso n for Shifting Trends – From Mobilit y to Accessib ility
The transp ortation world has been experiencing a shift in trends from traffic – based analysis
to mobility – oriented analysis to accessibility – based analysis. These concepts are all related
in such a way that traffic is a subset of mobility and mo bility is a subset of accessibility. (Litman
A huge dilemma on vehicle and driving policies revolved around whether mobility or
accessib ility should be enhanc ed. Should policies fulfil what the public wants which is
increased driving by accommodating growing levels of vehicle travel or should these policies
focus on limiting driving so as to reduce environmental impacts and other costs? The former
policy that is under consideration is far more politically palatable but is becoming increasingly
unaffordable. The latter implies reversing tr end s and going against American tr aditions of
freedom of movement. So the pract ical approach is to improve vehicle and fuel te chnologies
tha t will reduce e nvironmental impacts without limiting driving but this will lead to increased
driving that will surpass capacity in the future. Another ongoing problem is that a significant
part of the population cannot drive and do not have acc ess to a car due to income, age and
ability issues. An alternative approach that is increasingly attaining support is reducing driving
needs by bringing activities closer to home and improving transit , biking and walking facilities
by enhancing accessibility . This approach forms the basis for the shift from mobility to
accessibility through road building.
Scholars argue that accessibility metrics reflect the purpose of transportation best – to reach
destinations rather than t o be in motion which is what mobi lity metrics is mainly focused on.
Accessib ility metrics also involves mobility and proximity which is an advantage as it widens
the scope for detailed analysis, as seen in fig 1, mobility is a subset of accessibility.
Acces sibility – based planning offers a wide range of solutions to transportation problems and
also changes how we think – this shift changes what we consider the systems ‘ center – traffic
– based planning places a utomobiles at the center w hile accessibility – based planning places
people at the center of the transportation system. Planning practices su ch as evaluations
based on travel speed and distance which favour faster modes over slower modes, travel
statistics that ofte n undercount and undervalue non -motorized modes of transportation by
ignoring short trips , children ‘s travel etc., recognition of benefits of increased vehicle traffic
volumes and speeds and overlooking walkability and land use accessibility result in decisions
that increase mobility but reduce accessibility but do not provide optimal solutions. They are
not detail oriented leading to distortion and skewed results which do not provide accurate
and up to date information. Differ ent planning issues require differen t methods to account
for users, mod es, perspectives etc. Accessib ility – based analysis takes into consideration all
these factor s and offers a range of possible solutions to transport p roblems.
Example 1 – Neighborho od planning requires more walkability analysis while regional planning
requires more facilities analysis like, transit, rail and automobi le analysis.
Example 2 – Consider a school experiencing congestion, traffic an parking problems. Traffic –
based analysis would suggest expansion of road and parking facilit ies, mobility – based
analysis wou ld suggest improving school bus facilities while accessibility – based analysis
would consider alternative factors and suggest walking an d cycling impro vements and
provide incentives to encourage students and staff to reduce vehicular tr ips and also try to
reduce dista nce between homes and schools. These measures are cost effective a s they
consider ben efits and costs.
Obstacles to Accessibility – Based Evaluations
Some of the obstacles are –
• Theoretical soundn ess (Weakness of tools)
• Political c hallenges
• Local land use control
• Lack of constituency
Work To Be Done
The next sect ion will deal with how the obstacles of accessibility – based evaluations can
be overcome with a detailed explanation of each obstacle. The final question that focuses
on effects of mobility and proximity on accessibili ty in different contexts will be explained
by referring to a case study on evaluating accessibility in two regions – San Francisco and
Washington D.C. by analysing the effects of mobility and proximity separately on
accessibility – based eva luations.
Expected findings include –
• Central Washi ngton D.C. is a high accessibility zone but due to land use restrictions
there are constraints on population thus limiting the i mpact of accessibility zones
on accessibility . (Accessibility zones ensure that significant shares of population
have the opportunity to reside in zones such that facilities are accessible equally)
• Only 5% of Washington ‘s populat ion lived in the most accessible zones as
compared to 9% for San Francisco
• Transit facilities are better in Washington D.C. in comparison to San Francisco as it
offers large number of people with the opportunity to live in high – accessibility to
• Mobility outweighs proximity in its effects on accessibility in San Francisco due to
high speed road s while the case is the rever se in Washington D.C. However,
accessibility to destinations is higher in San Francisco as the effects of mobility
positively influencing accessibility is higher than the positive effects of proximity
in Washington D.C.
The data for comparative studies is obtained from US Census Bureau, US Department of
transportation database, Federal Transit Administration and National Transit Database.
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Joe Grengs, J. L. (n.d.). Inteermoetropolitan Comparison of Transportation Accessibility:
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Jonathan Levine, J. G. (n.d.). Accessibility -Based Evaluat ion of Transportation and Land -Use.
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