Newly developed link performance functions incorporating the influence of on-street occupancy for developing cities: study on Dhaka City of Bangladesh
On-street occupancy (legal or illegal) makes a substantial fraction of the traffic flow in many developing countries like Dhaka City of Bangladesh and is often the source of localized traffic congestion due to road capacity reduction. In developing countries, especially, illegal occupancy is prevalent. However, little has been done in literature to incorporate the influence of such occupancy on traffic performance. This study therefore attempts to fill in this gap. To the authors' best knowledge, this is the first attempt in developing countries. Taking Dhaka City as an example, this study first conducted a probe vehicle survey to collect the information about travel time over the course of a day (only workdays), which is divided into four time periods (different between Ramadan and non-Ramadan periods), in August and September, 2009. At the same time, on-street occupancy was also counted with respect to each time period. As a result, 30 road sections (links) at Dhaka City Corporation area were selected randomly over the city considering main corridor. Next, using the collected data as well as relevant data from secondary sources, this paper developed new link performance functions that recommend the updated volume - delay relationships by incorporating the influence of on-street occupancy. The functions were estimated for both peak and off-peak hours, and several other types of functions were also estimated for comparisons, where a constrained non-linear regression method was used for the estimation. Empirical studies statistically confirm the effectiveness of the proposed link performance functions. Finally, it is found that completely eliminating on-street occupancy could shorten travel time by more than 20%.