Estimating free flow speed using Google Maps API: accuracy, limitations, and applications

The Free-Flow Speed (FFS) is a key parameter used extensively in traffic analysis and in developing both macroscopic and microscopic transportation models. FFS is always recommended to be measured at site, and this poses a problem of time, cost, effort, risk, and associated logistics. This paper presents a new approach for estimating the FFS by making use of the Application Programming Interface (API) for Google Maps. In particular, the proposed approach utilizes free travel times (FTT) obtained through Google Maps API (GMAPI). Data from GMAPI were compared with similar data collected using Moving Car/GPS on major roads in Greater Cairo in Egypt. Roads were divided into distinct segments considering the minimum length of segment on each road. All data were collected during free traffic flow conditions. Comparison and statistical tests of paired two samples confirmed the high accuracy of FTT and FFS values obtained from GMAPI. Three applications were presented in this paper utilizing the estimated FFS values. First, the legal speed limit was evaluated against the free-flow speed, and odd segments were identified for further actions. Second, sharp curves on a major road were evaluated for design consistency and results confirmed the possibility of improving safety conditions on such road. Third, FTT and FFS values obtained from GMAPI were utilized in developing the transportation model for a medium-size city in Egypt, especially in coding and validating the road network. The network validation results ensured that FTT and FFS values obtained from GMAPI can lead to robust transportation models. The general findings of this research promise more applications of Google Maps API in various traffic applications.