What causes inaccuracies in calculated travel times?
We measure traffic volumes and congestion levels to calculate highway speeds. Under most circumstances, high volumes plus high congestion equals low speeds and increased travel times. Conversely, low volumes plus low congestion equals higher speeds and decreased travel times. However, there are times when those equations break down. For example, during snow, ice or heavy rain, drivers should reduce speeds and increase stopping distances. The vehicle detectors will measure the low volumes and low congestion, but not see the reason – the weather – and will produce inaccurate travel times as a result. Because the travel times are predictions based on current conditions, they obviously cannot include delays caused by future accidents or other unusual developments. Unforeseen accidents, stalls, and other incidents consequently may cause the calculated travel times to be unrealistically low.
