Congestion pricing strategy has been recognized as an effective countermeasure in the practical field of urban traffic congestion mitigation. Despite the positive effects of congestion pricing, its implementation has faced problems. This paper investigates the issue of environmental equity in cordon pricing and a park-and-ride scheme. Although pollution decreases inside the cordon by implementation of cordon pricing, air pollutants emission may increase in some links and in the whole network. Therefore, an increase in air emissions in the network means more emission outside the cordon. In fact, due to the implementation of this policy, air pollutants emission may transfer from inside to outside the cordon, creating a type of environmental inequity. To reduce this inequity, a bi-level optimization model with an equity constraint is developed. The proposed solution algorithm based on the second version of the strength Pareto evolutionary algorithm (SPEA2) is applied to the city network in Tehran. The results revealed that it seems reasonable to consider environmental equity as an objective function in cordon pricing. In addition, we can create a sustainable situation for the transportation system by improving environmental inequity with a relatively low reduction in social welfare. Moreover, there are environmental inequity impacts in real networks, which should be considered in the cordon pricing scheme.

This paper considers the issue of air pollutants emission for the optimal and sustainable determination of cordon location, toll level, and price of park and ride (P&R). Although air pollutants emission decreases within the cordon by the implementation of cordon pricing scheme, it may increase INTRODUCTIONTraffic congestion has become one of the most severe social problems in modern societies. For years, adding additional capacity has been the solution for the rising level of congestion [1]. However, such an approach is subject to many spatial and financial constraints. Furthermore, providing more road space has been proven to be self-defeating in congested areas, because increased capacity will soon be occupied by induced travel demands [2,3]. Thus, in order to alleviate roadway congestion, road congestion pricing has been introduced.Congestion pricing was first suggested by investigating a sample of a congested road and expressing some ideas about externalities and optimal congested charges by Pigou (1920). The fundamental concept of pricing is so simple: prices should be higher under congestion conditions and lower at less congested times and locations in order to prevent excessive use [4].Recently, road pricing issue has widely attracted the attention of economists and transportation researchers, due to growing prominence and changing nature of urban transportation problems faced by modern cities [5][6][7].Road pricing theory is based on the fundamental economic principle of marginal cost pricing. It indicates that the users who use congested roads have to pay a toll which is equal to the difference between marginal social cost and marginal private cost in a way that social surplus increases [8]. The marginal cost pricing, unlike its full theoretical basis, is of little practical interest. Therefore, the second-best pricing method has attracted interest recently [4]. In the second-best pricing method, toll is only charged over a subset of links of the network. Four types of toll charging scheme in road network seem to be more popular: travel-distance based charging, travel-delay based charging, linkbased charging, and cordon-based charging [9].Recently, in some countries, a cordon pricing scheme has been used, instead of pricing on separate individual links, in order to reduce traffic demand in central congested urban areas [10][11][12][13]. In the second-best pricing, simultaneous determination of toll locations and toll level on a network is practically important [14][15][16]. In addition, the effect of value of time (VOT) on the pricing problems has been investigated in some of the previous studies [17]. In the presence of heterogeneous users with different VOTs, various network equilibrium models have been developed either by assuming a discrete set of VOTs for several distinct user classes or by a continuously distributed VOT across the whole population [18][19][20][21][22][23]. Moreover, in other studies, equity issues and revenue redistribution in congestion pricing have been investigated [24...

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