Demand Responsive Transit (DRT)

Demand-responsive transit (DRT) is often seen as a combination of regular public transit services (fixed route, fixed schedule) and completely personalised taxi services (flexible route, flexible schedule). They are often used where traditional public transport services are lacking, or not cost-effective, to cover the demand areas. There is often a focus on the elderly or mobility-impaired populations when thinking of DRT, but they can also be used to effectively close the first/last mile problem, or serve as additional services when needed.

• There are various different elements that can define a service as ‘demand-responsive’, and they can be deployed in a variety of situations.

• Due to the flexible nature of DRT, sustainability can be increased by using ‘right-sized’ vehicles for the current requirements.

• They can be used to close the gaps in traditional public transport services if a regular service is not cost-effective, or can provide additional services to the elderly or mobility-impaired populations.

• DRT is often seen as a combination of traditional public transport and privately organised taxi services.

Some common elements of demand-responsive transit (DRT) include (Davison et al., 2012):

  • DRT can be situated between regular public transport services (which are usually served by buses) and completely personalised services provided by taxis.
  • DRT services can be flexible on any of the following features (or combination of these features): route, origin–destination pattern and timetable. When routes are fixed, they fall in the category of jitneys. When times are fixed but routes are variable, they fall under the denominator of vanpools.

Some authors include pre-booking as an element of the definition (Wright, 2013), which would then be the defining element compared to microtransit, which uses more technologically advanced booking options.

There are also ‘hybrid’ forms of DRT, combining a fixed route core allowing pre-booked deviations (up to a predefined maximum distance) and hail and ride on the fixed route section (Mulley et al., 2012).

Potential target markets for DRT services are (Davison et al. 2012, Wang et al. 2015; Neven et al. 2015; Ryley et al. 2014):

  • Market segments where demand is too low for conventional buses (e.g. rural areas, night and weekends) or where greater flexibility is needed than what can be provided by conventional buses. In these cases, DRT targets the general public, with schoolchildren as important sub-segment. In rural areas, DRT can also provide a feeder service to conventional public transport systems.
  • The elderly and mobility impaired (including non-emergency patient transport services), and, more in general, those who can afford neither private cars nor taxis. In Europe, this would be the typical clientele of DRT in an urban context.

DRT is close to, but distinct from, semi-flexible bus routes, which “include a reference (nominal) route that serves fixed regular bus stops; however, when there are requests from clients with limited mobility, one or more of the vehicles serving the route may diverge from this nominal path, pick up the clients from their origin and eventually drop them to a regular bus stop or to a special destination” (Dikas and Minis, 2014). Note that, in this concept, the “regular” bus must be able to take on board paratransit clients (which may include mobility impaired people).
DRT, especially when uniquely focusing on mobility-impaired people, is costly, and often requires public financial support (Davison et al., 2014). Another solution is to rely on volunteers to drive the vehicles (Neven et al., 2015). A case study in The Netherlands has revealed that those volunteers are often retired themselves. Performing these services gives them a purpose and also helps them maintain social contacts. Thus, volunteer-based systems are not just a way to save money; they can also improve social cohesion in rural communities (Schotman and Ludden, 2014).

If conventional bus services are subsidised (or compensated for Public Service Obligations), then cuts in central governments funding can induce local authorities to consider DRT as an alternative (Wright, 2013).

In Europe, DRT was initially targeting mobility impaired people, but as a result of the European accessibility and social inclusion agenda, there has been a move to accessibility for all.

DRT has also increasingly been seen as means to provide accessibility in rural areas, and to provide feeder services to conventional public transport (Mulley et al., 2012; Wright, 2013). In general, the cost of provision of these services appears to be high, and, in some countries, the supply of these services has been discontinued (Wright, 2013). Strict eligibility restrictions for DRT targeting audiences such as the mobility impaired can lead to higher costs of provision.

Depending on the market served, DRT services are provided by minibuses or mid-size vehicles (22 to 30 seats) but also by taxi operators (Wright, 2013). Wright (2013) has developed a methodology to derive the optimal vehicle size for a given demand and average trip length. Taxis provide more cost effective DRT services in areas where demand is lowest and more dispersed; minibuses (perhaps provided by social/voluntary enterprises) work better on semi-fixed route patterns in more densely populated areas”. Wang et al. (2015) find that the current level of evidence on optimal vehicle sizes remains weak. In regions with high seasonal variability (such as touristic areas), taxis can replace buses during the low demand season (Mulley et al., 2012).


The market segment of the elderly has evolved drastically over the last decades. On the one hand, people over 65 years have become more active and mobile. On the other hand, increased life expectations have resulted in an increasing number of people over 85 years, while important reductions in mobility are observed when people reach the age of 80 (Battellino and McClain, 2011). The extent to which travel by elderly people also includes trip chaining (for which traditional public transport is not well suited), varies from location to location, but the need for a door-to-door service appears to be crucial (Wang et al., 2015).

This growth in the number of mobility impaired people will not only affect the demand for DRT directly, but also through changes in the number and the spatial patterns of possible destinations such as health centres (Deka and Gonzales, 2014).

ActiveAge (2008) points out that, for elderly people, barriers to using public transport are not limited to the physical difficulty of boarding and alighting the vehicle, or to the difficulty of moving around within the vehicle with a wheelchair or a walking aid. Indeed, these barriers also include the stress of getting to the bus stop and of using automated vending machines.

Other stressors are “risks of slips or falls, emergency evacuation, anxiety of waiting at bus stops and handling fares, unfamiliarity of surroundings, technologies or the services themselves, and the ongoing fear of violence

or threats (portrayed by the media) that appears to be a more regular occurrence in cities”.


In practice, DRT confronts a range of challenges, the most important of which are (Davison et al., 2012; Ronald et al., 2015; Mulley et al., 2012; Daniels and Mulley, 2012; Nelson et al., 2010; Enoch et al., 2006):

  • When they are overly flexible in terms of schedule and /or route (and their travel times thus become too variable), they can become unsuitable to serve as feeder service to public transport hubs in urban areas.
  • The routing decisions for DRT are very complex to model and optimize. Some of these complexities arise from the difficulty to predict behavioural responses to late-running services or no-shows by the clients.
  • DRT services basically perform taxi services at PT prices. As a result, they can be perceived as unfair competitors by traditional taxicab services.
  • Despite the gradual extension of the scope of the services, there is a strong perception in some countries that DRT is only for mobility impaired people. This hampers the inclusion of DRT in the standard public transport offer.
  • DRT is usually not included in transport planning apps.
  • When DRT is provided by public transport companies who are used to serve captive markets only, there is insufficient experience with marketing to attract new clients.

Potential futures for DRT

The general expectation is that, due to ageing populations, the demands for DRT will continue to grow (Neven et al., 2015).

There are also some trends that increase the potential for DRT (Davison et al., 2012; Ryley et al., 2014; Mulley et al., 2012; Nelson et al., 2010):

  • An increasing feeling that conventional PT is inflexible and unreliable, especially taking into account that individual requirements can vary over time.
  • With increasing sprawl, conventional public transport can become unviable.
  • Public authorities show an increasing interest in DRT as a means to address inclusion of some specific targets groups, but also to achieve modal shift.
  • On-line bookings could make DRT more convenient for the general public, but not for the target audience of “socially motivated” DRT (such as elderly people or mobility impaired ones).
  • Some niches (such as airport shuttles) have already proved to be commercially viable.
  • In Europe, there is potential to use DRT in orbital journeys in suburban and peri-urban areas while ‘traditional’ PT is used for radial routes.
  • DRT could expand into goods delivery (e.g. of library books, prescriptions and post/parcels) as an additional source of income. There may also be untapped potential for transport in the “night time economy”.
  • The most important component of variable costs are the wage costs of the drivers (at least, in the schemes that are not volunteer-based). With automated mobility, this issue will disappear, and this will increase the potential of DRT as a feeder mode for high capacity public transport.
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