policymakers demonstrate

Skilled Cities and Efficient Urban Transport 399
increases. All this implies that it is a priori unclear how the causality runs. This
has led Duranton and Turner to study the congestion problem in American cities
for the years 1983, 1993, and 2003, using modern econometric techniques.
Their conclusions cast serious doubt on the merits of infrastructure-based congestion
policies. First, Duranton and Turner confirm that new roads and public
transport generate more traffic. What is less expected, but more important, is
that in the absence of road pricing and for some types of roads, ‘new road capacity
is met with a proportional increase in driving’. But where do the additional
travellers come from? Again, the answer is not the one that comes immediately
to mind: ‘the law of traffic congestion reflects traffic creation rather than traffic
diversion’. New cars and new trucks share the responsibility for the extra trips
almost equally. Last, whenever the road capacity is extended and road use is
not appropriately priced, the road extension will attract PT passengers back to
driving cars. This reduces frequency in the use of PT, a vicious circle that may
lead to the disappearance of the PT alternative.
In sum, work by Arnott, Duranton, Turner and others have a major implication
that runs against standard policy recommendations: when road pricing
is not implemented, building new roads might not be the appropriate policy
to reduce traffic congestion. Therefore, congestion pricing is back to centre
stage as the main tool to curb urban congestion. Despite the lack of enthusiasm
of public policy-makers for this instrument, the impressive number of
results obtained by urban transport economics should encourage governments
and other authorities to evaluate new transport projects against smart pricing
schemes.
Whenever we consider extending current road or PT infrastructure, we
should keep in mind that new technologies may enhance the effective capacity
of the existing transport system (Winston and Mannering, 2014). For example,
the capacity of the current road infrastructure may be enhanced by software
applications that facilitate ridesharing. In the long run, vehicle-to-vehicle
communication may increase the capacity of a road network by coordinating
conflicting traffic flows and by using the stock of cars more intensively, freeing
urban space from parking. In the case of public transport, new technologies may
also lead to a better use of existing capacity. For example, better software may
generate ‘on demand’ collective transport. When there is a capacity shortage,
pricing is crucial to using capacity optimally, while road pricing also stimulates
the development of new technologies.
9.7.2 The Wider Benefits of Urban Transport Projects and New
Developments in Assessment Methods
There is growing empirical evidence that big urban transport projects lead to
changes in the city form. García-López et al. (2015) have looked into the effects