Arriving anywhere on time is a matter of experience, educated guesswork and luck when you plan a trip by car. Even if you check maps, road conditions and traffic reports, a time of arrival remains an estimate. Google Maps uses a mix of travel variables that includes speed limits, traffic conditions, construction and weather to estimate arrival times.
Development of Google Maps
Since its online introduction in February 2005, followed by mobile phone support two months later, Google Maps has continually refined the way it collects and uses data to support maps and driving directions. The database uses official speed limits, recommended speeds, historical averages -- including for rush hours in some cases -- and real-time data obtained through crowdsourcing to calculate the most accurate travel times. In 2013, Google redesigned both desktop and mobile versions of Maps, incorporating traffic, construction and other potential delays in the directions given.
Speed limits provide a basis for the algorithms used by Google Maps to establish travel times. In locations where traffic information is scarce, the estimated time of arrival calculation may depend on published speed limits more than driving conditions, previous users' travel times or real-time information. Basing travel time on published speed limits for areas with little data due to low traffic density provides reasonable estimates, because the areas themselves are subject to few traffic influences.
Identifying specific ways that factors other than speed limits alter prediction algorithms is difficult. Google protects this proprietary information from competitors such as Apple Maps and Bing Maps. Mobile users who enable My Location in Google Maps send anonymous data about the speed and location of their travel. Collected and combined, this aggregate data goes into a database and is returned to Google Maps to reflect real-time driving conditions. Users also weigh in on driving conditions by using the "Report a problem" option in Google Maps, with which users report map errors and driving-condition changes.
Arriving on Time
Google Maps produces accurate and frequently updated estimates of travel times, although with limits to its precision. The weighting of real-time data is unpredictable, because any mobile Maps user may opt out of participation, making the size of crowdsourced data variable. With insufficient real-time samples, published speed limits weigh heavily in traffic speed calculations. Because estimating time of arrival requires a look into the future, even the best algorithms built on official speed limits and adjusted for real-time conditions can't anticipate every factor.