Demand Responsive Transport

Taxonomy and description

Demand Responsive Transport is an element of a wider set of services, often referred to as Paratransit.  Other authors have used the term Flexible Transport Services.  We start by defining each of these.

Paratransit
The distinguishing feature between taxis and buses as forms of public transport is characterised by the level of “personal service” provided. Bus and rail services are provided for larger numbers of people, whereas taxi services provide an individual service with a more personal interaction between the driver and the user. Providing the middle ground in this service level spectrum lies paratransit (Rimmer, 1980; Bakker, 1999; Lave and Mathias, 2000). Rimmer (1980) defines paratransit as a “nebulous mass of transport organisations, technologies, and services that lie somewhere between conventional and personal transit in price and quality”.

Demand Responsive Transport
In this category of paratransit lies Demand Responsive Transport (DRT). Brake et al (2003) state that “DRT services provide transport on demand from passengers using fleets of vehicles scheduled to pick up and drop off people in accordance with their needs.” In the same vein, Logan (2005) echoing Raje et al (2003) mention that “DRT is an intermediate form of transport, somewhere between bus and taxi and covers a wide range of transport services ranging from less formal community transport through to area wide networks”. In a recent report by the Commission for Integrated Transport  (CfIT, 2008) in the UK, the following is given as the definition: “Any form of transport where day-to-day service provision is influenced by the demand of the users. In the UK these tend to be small-scale, for a defined region or specific community of people, and be door-to-door. ”  Enoch et al (2004 p20) sum this up succinctly; stating that “DRT is neither fish nor fowl” – it is neither taxi, nor minicab or bus”.

The varied definitions of DRT all focus on the distinguishing feature of DRT: DRT is specifically adapted (generally in its routing) to meet the demands of the users, and thus contrasts with conventional fixed route public transport services.  The concept of DRT has been in existence since the 1970s (see for example Higgins, 1976).  However there has been renewed interest in the concept of DRT in recent years, as a means of meeting  the needs of increasingly dispersed populations and to provide viable public transport based alternatives.

Flexible Transport Services

As mentioned above, the distinction between DRT and conventional public transport is the distinction between the levels of personalisation in the service provided. Buses tend to operate a fixed route specified in advance while DRT services tend to provide close to door-to-door taxi like services. However this is not the only facet of flexibility as the following diagram in Figure 1 shows.

Figure 1: The Demand Responsiveness of Public Transport (Source: Brake et al 2007)

This has therefore led to the usage of the more general term “Flexible Transport Services” (FTS; see Brake et al 2007). In the spectrum of flexibility, DRT is only one category of FTS. Other FTS include community and special needs transport as well as car sharing and car pooling schemes (Ferreira et al, 2007).

FTS is a subcategory of what Walker (2008) refers to as “purpose driven Public Transport”. To underscore this point, Ferreira et al (2007) point out that flexible transport is designed to be flexible, integrated and customer centric. The focus is on the customer (i.e. personalised transport).

Types of DRT service

DRT can also be classified (TRL, 1977) into its variants and service offerings:

• Route
• Stops
• Schedule
• Fare
• Driver

Route

With regard to the categorisation of the routings of DRT services, the following definitions are in common use (DfT (2002)).

• Many to one: This routing pattern involves a vehicle picking up individual passengers from locations specified by them (perhaps their home), and taking them to a single destination – with the vehicle arriving either in accordance with a published timetable, or within a time window. This has the focus on bringing people to a fixed point (e.g. a bus or rail interchange or even a park and ride site).
• One to Many: This is a routing pattern where passengers are picked up from a fixed boarding point and taken to disparate destinations, on demand.
• Many to Many:  This is the routing which allows the service to pick up passengers from various locations, on demand, and taking them to disparate destinations (within a defined geographical area of operation), again on demand.

Enoch et al (2004) introduced some definitions regarding DRT operations which can be thought of as an “evolution” or growth model for DRT operations

• Interchange DRT: DRT for the purpose of providing feeder links to conventional public transport.  
• Network DRT: As part of an overall network of public transport service provision, DRT services are operated only at particular times or in particular routes or both.
• Destination Specific DRT: similar to Interchange DRT but could encompass particular destinations such as airports, employment locations, health, shopping, social and leisure destinations.
• Substitute DRT: DRT replaces conventional public transport.

At one end of the spectrum, DRT services can be fully flexible very much like a conventional taxi service. However, in practice, DRT services tend to follow a fixed route with deviations as requested by the passengers.

Stops

DRT services generally aim to provide a door to door service. At the same time, some services offer the ability of passengers to board and alight at conventional bus stops. With the advent of technology, it is also possible to request the service in real time for immediate travel at equipped bus stops.

Schedule

The timing points of the DRT services could follow that of a conventional bus service with published frequencies. At the same time, they may only operate only when there is sufficient customer demand.

Fares

Fares may be charged on an individual basis (as in a conventional bus services) or could be paid for on a group basis (in the case of shared taxi schemes)

Driver

The driver of the vehicle might be on a voluntary basis (e.g. DRT provided by charitable organisations or Community Transport organisations) or could be employees of the service provider.

Technology and Operation of DRT Services

As Figure 1 shows, the routes of conventional public transport are fixed in advance through standard scheduling methods. The type of vehicle and the number of drivers required to operate the service is well known ahead of time. However, in the case of DRT services, the entire process is different as shown in Figure 2.

Figure 2: Illustration of DRT Service and Operation
Source: Mageean and Nelson (2003)

The user of the service telephones into a dispatching centre to book a journey (the time limit for bookings varies considerably). Historically, the primary method of booking the DRT service was via the telephone. Using advances in transport telematics, it is possible also to book journeys via the internet and short messaging service (mobile phone sms) (Engels and Ambrosino (2003).

Booked journeys are assigned, via despatching systems which are very similar to those for private hire vehicle services except that vehicles are usually shared with other passengers. The vehicle type used for the journey may not be decided until the service is operated, although some small schemes may only have access to one or two minibuses, or for a community scheme run by volunteers, drivers’ own personal cars. Stops are usually determined only at the passenger’s request.

In the simplest DRT systems, scheduling (the process of assigning vehicles to each run and drivers to vehicles) may be done  manually by assigning vehicles to collect passengers (Enoch et al, 2004).

In more comprehensive operations computerised scheduling systems are employed. The issue of technology using the concept of transport telematics has been discussed in prior research (e.g. Ambrosini et al, 2003). Various research program funded by the European Commission (SAMPLUS (1999), FAMS (Ambrosini et al 2004) INVETE (2002))  marked the transition of DRT to its second phase. In this second phase, it was  demonstrated that the application of the field of transport telematics to DRT was possible.

The main components of the Telematics based DRT system are
1. Travel Dispatch Centres (TDCs);
2. Devices for users to access the DRT system;
3. On-board units;     
4. The communications network.

Telematics-based DRT systems are organised via TDCs using booking and reservation systems which assign passengers to vehicles and optimise the routes. Automated Vehicle Locationing (AVL) systems provide real-time information on the status and location of the fleet for the route optimising software.