Abstract
Online real-time traffic data services could effectively deliver traffic information to people all over the world and provide large benefits to the society and research about cities. Yet, city-wide road network traffic data are often hard to come by on a large scale over a longer period of time. We collect, describe, and analyze traffic data for 45 cities from HERE, a major online real-time traffic information provider. We sampled the online platform for city traffic data every 5 min during 1 year, in total more than 5 million samples covering more than 300 thousand road segments. Our aim is to describe some of the practical issues surrounding the data that we experienced in working with this type of data source, as well as to explore the data patterns and see how this data source provides information to study traffic in cities. We focus on data availability to characterize how traffic information is available for different cities; it measures the share of road segments with real-time traffic information at a given time for a given city. We describe the patterns of real-time data availability, and evaluate methods to handle filling in missing speed data for road segments when real-time information was not available. We conduct a validation case study based on Swedish traffic sensor data and point out challenges for future validation. Our findings include (i) a case study of validating the HERE data against ground truth available for roads and lanes in a Swedish city, showing that real-time traffic data tends to follow dips in travel speed but miss instantaneous higher speed measured in some sensors, typically at times when there are fewer vehicles on the road; (ii) using time series clustering, we identify four clusters of cities with different types of measurement patterns; and (iii) a k-nearest neighbor-based method consistently outperforms other methods to fill in missing real-time traffic speeds. We illustrate how to work with this kind of traffic data source that is increasingly available to researchers, travellers, and city planners. Future work is needed to broaden the scope of validation, and to apply these methods to use online data for improving our knowledge of traffic in cities.
Highlights
By mid-century, the global population could very well reach 10 billion, with three out of every four people likely to be living in highly urbanized places
We address the following research questions: (i) Are there regular recurring patterns of data availability that differ between different cities? (ii) Are the real-time data measurements valid, and what challenges can arise with validation? (iii) What methods are efficient in filling in the missing data when real-time measurements are not available for some road segments? This section addresses these three questions to assist with using the data source for further analysis
We examine several areas where cities may vary and examine the data availability
Summary
By mid-century, the global population could very well reach 10 billion, with three out of every four people likely to be living in highly urbanized places. The rise of real-time and online traffic data has the potential to generally increase the availability of the data that form the basis of traffic planning and adaptive demand, but it is known that individual travelers are known to react by selecting their transport routes and modes in response to particular conditions of traffic data; main factors include traffic route delays, the reliability of data, and ambiguity aversion (BenElia and Avineri 2015; Chorus et al 2006). This clearly motivates a study of the availability aspect of heterogeneous traffic conditions. A scientific evaluation of this type of data that highlights the possibilities as well as the limitations is both timely and critical for travellers, researchers, practitioners, and private entities who can use the information to further models, tools, and make planning decisions for traffic in cities
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