In Business Analyst Web App, the Drive-Time analysis with traffic may cover a wider area compared to the result of the same analysis without traffic. This may be against the common assumption that running Drive-Time analysis without traffic must result in the maximum coverage possible as no traffic condition is applied.
Below are examples showing 15-minute Drive-Time areas in Santa Monica with three different traffic scenarios:
15-minute Drive-Time area without traffic
15-minute Drive-Time area with live traffic
15-minute Drive-Time area with traffic based on typical conditions for a specified time
When running Drive-Time analysis without specifying traffic conditions, the speed is computed based on average traffic speeds or posted speed limits. For areas with no traffic history available, posted speeds are used instead. If traffic history is available, the solver assumes the weighted average time it takes to travel across all times of the day and days of the week. Therefore, it is possible for travel speeds to be less than the posted speed limits, or less than live traffic or traffic history for a specified time. This explains why it is possible for the result to be a narrower coverage area when running Drive-Time analysis without traffic compared to the coverage area with live traffic or traffic history data. For more information on how Drive-Time areas work with live traffic or traffic history, refer to How Create Drive-Time Areas works.