The Design of Rapid Transit Networks - Location Science - page 565

by the system, often defined as the population living within a certain distance
threshold from stations. This limit has been fixed to 400 m or 5 min walk in dense
areas (Vuchic 2005 ), but it can grow to 1 km in less populated regions. Moreover,
the catchment areas of stations are not always limited to pedestrian traffic but also to
combined modes (Mesa and Ortega 2001 ). However, ridership is not only a function
of the distance to the line, but also of the design of the network (Gendreau et al.
1995 ). A better measure is the predicted trip coverage which can be measured
by origin-destination surveys, coupled with traffic equilibrium models. Potential
users are mainly interested in reducing their travel time. A secondary objective
of the passengers is to transfer between lines as little as possible. Of course this
can be included into a more general and difficult to measure concept of comfort
or generalized cost. Finally, the third group, that of construction and operating
companies, is mainly concerned with fixed and variable construction and operating
costs and revenues.
An existing rapid transit network can be evaluated by means of network measures
and indicators, but the same measures can also be used to evaluate potential
networks, in particular those resulting of the process of combining corridors. To
this end graph theory is a useful tool. Furthermore, these measures can be used
as objective functions or as constraints in mathematical programming models.
Musso and Vuchic ( 1988 ) have developed some network topology indicators
such as circle availability, network complexity and connectivity. They have also
considered service measures and utilization indicators. Laporte et al. ( 1997 )have
also measured the efficiency of rapid transit networks via the passengers/network
and passengers/plane measures. For example, these authors have shown that in a
circular city, triangle and cartwheel designs are preferable to star designs (Fig. 22.2 )
in terms of connectivity and travel directness.
Gattuso and Miriello ( 2005 ) provide a comparative analysis of 13 existing metro
networks with respect to 10 indicators. Other indicators such as regularity, service
availability, punctuality and reliability can be found in UITP ( 2011 ). Nowadays,
the values of some of these indicators are often presented in the technical reports
of operating companies. Whereas most of the early research on indicators and
measures concerns the description and efficiency of the networks with respect to
different topological indicators, in recent years we have witnessed the emergence of

a b c

Fig. 22.2 Three basic metro designs. ( a ) Triangle. ( b ) Cartwheel. ( c )Star