Journal of Geo-information Science >
The Impact of Travel Time Uncertainty on Accessibility under Different Measurements
Received date: 2022-04-23
Revised date: 2022-05-16
Online published: 2023-01-25
Supported by
National Natural Science Foundation of China(71971021)
National Natural Science Foundation of China(71901022)
Many scholars have focused on public transit accessibility, as the public transportation system plays more important role in commuting. Travel time uncertainty, which is caused by timetable and traffic condition changes, leads to uncertainty in accessibility. Ignoring travel time uncertainty may cause overestimation of accessibility. This overestimation may bring optimism about travel time to the commuter, and they may not reach their destinations on time. Therefore, it is essential to measure public transit accessibility realistically. Moreover, previous studies often use one measurement to calculate the influence of travel time uncertainty on accessibility and do not consider the differences between measurements. Different measures may be oriented to different infrastructure investment, therefore, understanding the results of different measures is also important. To fill these gaps, we first divided the study area (Shenzhen) into 1854 grids and collected millions of travel dataset and POI dataset from GaoDe Map. Then, this paper developed the travel time reliability by investigating the travel time distribution and standard deviation between OD pairs. We extended the generalized travel cost in accessibility measurements by incorporating travel time reliability. The static accessibility measurements use the generalized travel cost without considering travel time reliability. Furthermore, we developed four types of placed-based accessibility measurements to analyze the differences between accessibility with and without travel time uncertainty. The results in Shenzhen's case showed that travel time uncertainty increased accessibility at least by 5.80%, and at most by 95.04% in the whole area. The order of models from minimum to largest increase was that: the potential model, the time distance model, the cumulative opportunity model, and the Gaussian model. The accessibility of Gaussian model increased by 59%~553%, while the generalized travel cost threshold increased from 45 min to 120 min. Additionally, the impact of travel time uncertainty on accessibility existed threshold effect, the higher threshold, the smaller the degree of reduction. The results indicated that ignoring the travel time uncertainty may underestimate the effect of improving the transit system. From the perspective of spatial patterns, the influence of travel time uncertainty covers the whole region. The value of overestimation was high in the area with a high level of accessibility, the degree of overestimation was high in the area with a low level of accessibility when travel time uncertainty was ignored. The median of overestimation degree can reach 77.1%. The potential model had the minimal variation in accessibility classification and the cumulative model generated the maximum variation. The results provide the insights that users should pay more attention to the impact of travel time uncertainty on accessibility. Additionally, government should take care on the model choice and consider the results of different measurements comprehensively, as different models lead to different decisions.
XIAO Zhongsheng , XU Qi , MAO Baohua , WEI Runbin , FENG Jia . The Impact of Travel Time Uncertainty on Accessibility under Different Measurements[J]. Journal of Geo-information Science, 2022 , 24(11) : 2102 -2114 . DOI: 10.12082/dqxxkx.2022.220219
表1 不同阈值和不同模型下的平均可达性Tab. 1 Mean accessibility under different thresholds and measurements |
模型类别 | 是否考虑行程时间 不确定性(Y/N) | 广义出行时间成本阈值/min | |||||
---|---|---|---|---|---|---|---|
45 | 60 | 75 | 90 | 115 | 120 | ||
时间距离模型 | Y | 0.3440 | 0.3440 | 0.3440 | 0.3440 | 0.3440 | 0.3440 |
N | 0.3748 | 0.3748 | 0.3748 | 0.3748 | 0.3748 | 0.3748 | |
潜力模型 | Y | 31.92 | 31.92 | 31.92 | 31.92 | 31.92 | 31.92 |
N | 33.84 | 33.84 | 33.84 | 33.84 | 33.84 | 33.84 | |
高斯模型 | Y | 61.43 | 401.46 | 1179.76 | 2490.61 | 4611.32 | 7439.09 |
N | 112.40 | 569.11 | 1554.64 | 3228.35 | 5722.88 | 9075.45 | |
累计机会模型 | Y | 349 | 1685 | 4346 | 8542 | 14 902 | 22 803 |
N | 581 | 2252 | 5501 | 10 716 | 18 018 | 27 184 |
表2 阈值变化对可达性增幅的影响Tab. 2 The impact of changes in threshold on accessibility (%) |
模型 | 是否考虑行程时间不确定性(Y/N) | 成本阈值/min | ||||
---|---|---|---|---|---|---|
60&45 | 75&60 | 90&75 | 105&90 | 120&105 | ||
高斯模型 | Y | 553 | 194 | 111 | 85 | 61 |
N | 406 | 173 | 108 | 77 | 59 | |
累积机会模型 | Y | 382 | 158 | 97 | 74 | 53 |
N | 288 | 144 | 95 | 68 | 51 |
表3 忽略行程时间不确定性对可达性的高估百分比Tab. 3 The degree of overestimation on accessibility (%) |
模型 | 成本阈值/min | |||||
---|---|---|---|---|---|---|
45 | 60 | 75 | 90 | 115 | 120 | |
时间距离模型 | 7.85 | |||||
潜力模型 | 5.80 | |||||
高斯模型 | 95.04 | 51.19 | 37.67 | 35.11 | 26.54 | 23.58 |
累计机会模型 | 59.50 | 32.65 | 26.43 | 25.93 | 20.76 | 19.15 |
表4 存在分类差异的栅格数量Tab. 4 The number of grids with classify difference |
模型 | 成本阈值/min | 平均数量/个 | |||||
---|---|---|---|---|---|---|---|
45 | 60 | 75 | 90 | 115 | 120 | ||
时间距离模型 | 103 | 103 | |||||
潜力模型 | 96 | 96 | |||||
高斯模型 | 344 | 338 | 171 | 169 | 236 | 129 | 231 |
累计机会模型 | 471 | 293 | 338 | 343 | 166 | 205 | 303 |
表5 存在分类差异的栅格的高估程度Tab. 5 The median degree of overestimation (%) |
模型 | 成本阈值/min | |||||
---|---|---|---|---|---|---|
45 | 60 | 75 | 90 | 115 | 120 | |
时间距离模型 | 7.51 | |||||
潜力模型 | 6.33 | |||||
高斯模型 | 150.6 | 50.6 | 27.4 | 47.5 | 27.7 | 29.6 |
累计机会模型 | 104.3 | 50.9 | 38.7 | 35.0 | 32.7 | 34.4 |
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