What Is the Mobility Measure?
The measure of system performance that concerns manufacturers, shippers and truckers is door-to-door trip time. For the border crossing measure to be useful, it should relate to this measure as closely as possible, but it should also be more comparative than simple travel time.
The best measure for the freight transportation system at international roadway border crossings is travel delay per truck trip through the first inspection point in the import country. The more detailed inspections downstream of this point are substantially related to issues such as the safety and welfare of the importing country, and the potential improvements are more related to the inspection process and the design of individual port operations. This will be measured for travel in both directions on both the northern and southern U.S. border crossings. Initially the focus should be on collecting this statistic at the major ports of entry, with refinements and automated data collection facilitating expansion to other ports.
The term "delay" will be defined relative to operations at relatively low volume. This standard allows the processing time that the inspection agencies need to accomplish their mission to be removed from the definition of delay. The processing time will be included in the low volume condition. Using a free-flow condition, similar to operations along a normal city street or freeway, is a standard that is not relevant unless the inspection process is greatly reduced through treaties or other agreements.
Figure 2 is an example of the three conditions (the lines illustrate the cumulative travel time for free-flow, low volume and roadway operations) and the delay estimate – the difference between the low volume and roadway operating conditions. This difference will be tracked throughout the day and the delay time for each hour will be multiplied by the number of trucks experiencing the delay. As a practical matter the data collection could be concentrated in periods when delay may occur.
For the purposes of this study, the following terms are defined:
- Baseline Travel Time – The time through the system at low volume conditions. For this report, the value used was that of the lowest hourly travel time in that direction for each day. This value represents the "no delay" travel time.
- Average Number of Open Booths – The average number of commercial vehicle inspection booths open and available for processing trucks at the initial import country's checkpoint. This figure is not used to compute delay but is useful to help understand the relationship between booths, traffic volume, and delay.
- Average Travel Time – The average amount of travel time through the data collection area from entry to exit for trucks entering the system each hour. The time the vehicle passes the advance point determines the time period label.
- Delay per Trip – The difference between the average travel time and the "no delay" time.
- Average Traffic Volume – The average hourly truck volume for the "season" or time of year being analyzed.
- Total Delay – The product of the average hourly truck volume and delay per trip.
For this study, two data collection locations were used in each direction. The first location was at a point upstream from the first point where trucks might experience delay in approaching the border and the second location was immediately after the primary inspection booths. Each data collector used a handheld computer to record license plate information of all commercial vehicles that passed their location. The computer would also store the time that each license plate was entered. The data from the two locations in each direction would be combined, allowing the determination of the travel time between each location throughout the time when most trucks were using the crossings. The number of matches are noted for statistical analysis and the travel time is noted for each hour. The travel time was assigned to the hour when the truck passed through the import country's primary customs inspection location as this was the only location that remained consistent throughout the data collection.
Data were collected at the following locations and shown in Table 1.
|Port of Entry||Survey Date(s)||Survey Time(s)||Inbound Average Daily Volume||Outbound Average Daily Volume|
|Otay Mesa, CA||July 17–19, 2001||6:00AM to 8:00PM||1,886||not available|
|El Paso, TX||June 26–28, 2001||8:00AM to 8:40PM||1,973||1,080|
|Laredo, TX||October 30–November 1, 2001||8:30AM to 7:00PM||2,956||3,048|
|Blaine, WA||July 10–12, 2001||7:00AM to 8:00PM||1,335||not available|
|Blue Water Bridge, MI||
|Ambassador Bridge, MI||
|Peace Bridge, NY||
The Buffer Time is a measure of travel reliability calculated by ranking crossing times of individual trucks at each port of entry. A crossing time for the 95th percentile of trucks is calculated, i.e., the time within which 95 percent of all trucks would have been processed through the point where they first experience delay and the exit from primary inspection of the import country. An average crossing time for all trucks is also calculated. The Buffer Time is the difference between the 95th percentile time and the average time for all trucks. The Buffer Time, then, represents the "extra time" a driver must budget to cross the border at the average time with a 95 percent certainty. This measure becomes particularly important as more and more goods are moved under the stricter requirements of such practices as just-in-time inventory/manufacturing where timely, dependable, and consistent goods movement is critical.
The Buffer Index is the Buffer Time necessary expressed as a percentage of average time, i.e., the extra percentage of time that must be budgeted to cross the border. This is the measure that will be the most comparable over the years and between the crossings as it serves to standardize the measure by remove differences in crossing length as an element.previous | next