Abstract
We propose a new method to estimate benefits of road network improvements, which allows to include the induced demand without arbitrary assumptions. Instead of estimating induced demand (which is nontrivial and hardly possible in practice), we search for demand induction where initial benefits are mitigated to zero. Such approach allows to formulate a dual measure of benefit, covering both the potential benefits and the likelihood of consuming them by the induced traffic. We first estimate benefits of road network improvement assuming that traffic demand is fixed. Consequently, we find demand model configurations at which the benefits of the new investment become null, i.e., all the initial benefits are consumed by the traffic demand growth. We call such states of induced demand the Lewis–Mogridge points of the analysed improvement. We select the most probable of such points and use it to calculate the proposed novel indicator μ, for which the initial benefits (obtained under a fixed-demand assumption) are multiplied with a demand increase rate needed to consume them. We believe that such measure allows to include the critical phenomena of induced traffic and, at the same time, to overcome problems associated with reliable estimation of induced demand. As we illustrate with the case of two alternative road improvement schemes in Kraków, Poland, the proposed method allows to estimate maximal threshold of induced traffic and to select scenario more resilient to induced traffic.
Highlights
Induced traffic, spurred by improvements in road networks, is nowadays a recognised phenomenon in transportation planning practice, especially in case of largescale development projects
(2) Induced traffic: new trips arising in response to improvements in quality of service in the road network. ese can be further subdivided into two main categories: (a) Direct induced traffic: typically, the short-term response that consists of shifts in trip destinations, trip chaining patterns, and trip frequencies
Research works of [18, 19] that were later captured in form of the well-known Downs– omson hypothesis emphasise that increasing road capacity eventually leads to rising travel cost in urban networks: the increase in private transport demand imposes higher externalities costs and exacerbates road congestion, and the corresponding reduction in public transport demand implies higher unit travel costs, which need to be offset with fare increases, service frequency reductions, etc
Summary
Induced (generated) traffic, spurred by improvements in road networks, is nowadays a recognised phenomenon in transportation planning practice, especially in case of largescale development projects. (b) Indirect induced traffic: changes in trip patterns which do not result directly from improvements in travel costs (times) but reflect the long-term increase in travel activities stemming from shifts in land-use patterns, new urban and residential developments, mobility and lifestyle changes, etc., which are in turn often facilitated by road network development [12, 13] This subcategory may encompass the “rippleeffects” in traffic flow itself such as induced traffic arising on an existing road link which was initially alleviated by a new road segment (e.g., construction of the city bypass). It follows that any expansion of urban road capacity is unlikely to be efficient unless it is correlated with a corresponding improvement of public transport system, since in the end the distribution of travel demand flows will adapt to an equilibrium state
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