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Understanding network travel time reliability with on-demand ride service data

Xiqun (Michael) CHEN, Xiaowei CHEN, Hongyu ZHENG, Chuqiao CHEN

《工程管理前沿（英文）》 2017年第4卷第4期页码 388-398 doi: 10.15302/J-FEM-2017046

摘要： Travel time reliability is of increasing importance for travelers, shippers, and transportation managers because traffic congestion has become worse in major urban areas in recent years. To better evaluate the urban network-wide travel time reliability, five indices based on the emerging on-demand ride service data are proposed: network free flow time rate (NFFTR), network travel time rate (NTTR), network planning time rate (NPTR), network buffer time rate (NBTR), and network buffer time rate index (NBTRI). These indices take into account the probability distribution of the travel time rate (i.e., travel time spent for the unit distance, in min/km) of each origin-destination (OD) pair in the road network. We use real-world data extracted from DiDi-Chuxing, which is the largest on-demand ride service platform in China. For demonstrative purposes, the network-wide travel time reliability of Beijing is analyzed in detail from two dimensions of time and space. The results show that the road network is more unreliable in AM/PM peaks than other time periods, and the most reliable time period is the early morning. Additionally, we can find that the central region is more unreliable than other regions of the city based on the spatial analysis results. The proposed network travel time reliability indices provide insights for the comprehensive evaluation of the road network traffic dynamics and day-to-day travel time variations.

关键词： network travel time reliability on-demand ride services travel time rate OD

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Anoxic phosphorus removal in a pilot scale anaerobic-anoxic oxidation ditch process

Hongxun HOU, Shuying WANG, Yongzhen PENG, Zhiguo YUAN, Fangfang YIN, Wang GAN

《环境科学与工程前沿（英文）》 2009年第3卷第1期页码 106-111 doi: 10.1007/s11783-009-0005-8

摘要： The anaerobic-anoxic oxidation ditch (A /O OD) process is popularly used to eliminate nutrients from domestic wastewater. In order to identify the existence of denitrifying phosphorus removing bacteria (DPB), evaluate the contribution of DPB to biological nutrient removal, and enhance the denitrifying phosphorus removal in the A /O OD process, a pilot-scale A /O OD plant (375 L) was conducted. At the same time batch tests using sequence batch reactors (12 L and 4 L) were operated to reveal the significance of anoxic phosphorus removal. The results indicated that: The average removal efficiency of COD, , , and TN were 88.2%, 92.6%, 87.8%, and 73.1%, respectively, when the steady state of the pilot-scale A /O OD plant was reached during 31-73 d, demonstrating a good denitrifying phosphorus removal performance. Phosphorus uptake took place in the anoxic zone by poly-phosphorus accumulating organisms could be used as electron receptors in denitrifying phosphorus removal, and the phosphorus uptake rate with as the electron receptor was higher than that with when the initial concentration of either or was 40 mg/L.

关键词： wastewater treatment anaerobic-anoxic (A²/O) oxidation ditch (OD) biological phosphorus removal denitrifying phosphorus removal