Measuring Improvements in the Movement of Highway and Intermodal Freight
percent of on-time arrivals
Reliability is an attribute of key importance to highway shippers. In fact, a number of reports noted that having predictable travel times may be even more important than average travel times. More than ever, logistics management emphasizes “just-in-time” delivery to reduce or eliminate storage and warehousing costs. Shippers schedule freight movements to account for travel delays and avoid peak period congestion to the extent possible. As a result, the rate of variation in travel time (unexpected delay) is of key concern.
Just like travel time measures, reliability measures are less useful if they focus on all travel. It would be important to focus on routes of particular importance to freight. Another weakness of these measures is that a high level of reliability does not necessarily reflect that conditions are good, only that they are consistent (e.g., it could reflect consistently slow or high-cost service). As a result, it would be useful to combine a reliability measure with a travel time or cost measure.
Hours of Incident-based Delay
Incident-based delay reflects increases in travel time that are unexpected, and therefore would be of particular importance for freight delivery schedules. It may be difficult, however, to identify what portion of total delay results from recurrent versus incident-based congestion. A composite measure of delay in various metropolitan areas or key freight nodes would need to be developed to be used as a national measure.
Variance in Travel Time
Variation in travel time also is a potentially useful measure that would be useful to examine for specific corridors or routes of importance to freight. However, depending on how the measure is developed it might reflect not only unexpected incident-based delay but also more expected seasonal, day-of-week, or time-of-day fluctuations in travel time.
Percent On-time Arrivals
Percentage of on-time arrivals is a potentially useful measure since it focuses directly on freight movements and reflects highway conditions. The advantage of the other reliability measures is that they directly represent highway conditions; the percent of on-time arrivals may reflect other factors as well. In terms of tracking progress over time, the measure is also limited because it could be a “moving target” in that schedules may be adjusted to account for worsening congestion or other factors that reflect lower quality service. Data availability also is an issue. On-time arrivals are tracked by private firms, but such information may not be publicly available.