cran
Auckland’s roading network is critically loaded. Over the New Year period,
driving around Auckland has been comparatively pleasant, with less traffic
congestion than usual. Contrast this with the usual state of the roads, when
even a relatively minor disruption such as rain leads to much longer delays.
However, this poor state of affairs also signals an opportunity. If even a
small increase in traffic volumes leads to increased delays, then, equivalently,
even a small reduction in traffic on the roads will decrease delays. Thus
encouraging more people to use public transport is an effective way to
improve traffic flows. Building more roads, on the other
hand, does not always have the desired effect. Traffic engineers are familiar
with the Downs-Thomson paradox, that increasing roading capacity
(whether by building new roads or widening existing ones) may just lead
to greater delays for everyone as shifts in traffic lead to ever greater
congestion, while the public transport system languishes.
How does this come about? If roads are improved, some commuters
shift from using public transport to private transport, and if the shift is
large enough then congestion on the roads returns to its previous high
levels, while the frequency of public transport declines in response to
reduced usage, which then pushes yet more commuters to shift to private
transport. This cycle may continue until an equilibrium is reached where
congestion on the roads is greater than it was previously, and public transport
less frequent, so the average delay for everyone has increased.
The paradox arises because most commuters choose their mode of
transport to minimise their own costs, without considering the effects of their
choice on delays for others. Road tolls or congestion pricing are one way of
forcing the whole transport system to a better operating point, by making road
use expensive compared with public transport. A friendlier solution that
would have a similarly positive effect is to make public transport cheaper!
Ultimately though, it is the individual’s choice that matters. Public or private
transport: even a small change in usage can make a difference.
---
Dr Ilze Ziedins
===============
我的话 :
这是我们系老师关于交通问题的文章。在这里可以发现,不是越多路越好的