Evaluation of Travel Time Methods to Support Mobility Performance Monitoring:
Ambassador Bridge (Page 4 of 5)
Data Collection Sample Size
Sample sizes are typically not a concern with videotape or handheld data entry devices, because the data collection includes a large number of vehicles. However, minimum sample sizes should be verified with variability values from field data. Early research found that sample sizes from 25 to 100 license matches were necessary for a given roadway segment and time period (Turner, et. al.). In general, there were sufficient records each day to meet this requirement.
Data Collection Equipment
As outlined in the "Data Collection Procedures" section above, handheld computers were used as the data entry device and proved adequate to the task. For the first week of data collection, Palm m100 model handheld computers were used. It was decided, however, that subsequent data collection should be done with Handspring Visors. The Handspring Visors use the same Palm OS (operating system) and have faster processing speeds (at least in side-by-side comparison with this application) and larger screen sizes than the m100 models from Palm Computing. Low-end models with 2MB of storage capacity were selected as the application and data size were projected to be well below this limit.
A custom application was developed for the Palm OS that allowed the data collectors to identify their locations (e.g., OB-1, IB-2), the number of open booths (primarily used for the customs inspection booths), special events or other comments, and license plate information. A screen shot of the application interface is shown in Figure 20.
Figure 20. Data Collection Device and Software Application.
The data were downloaded via a serial cable directly from the application into a text file on the field laptop computer, which was a Dell Latitude CPx H running with a 500 MHz Pentium III processor.
Data Collection Summary
Table 6 shows the number of commercial vehicle license plates recorded for each of the stations on each of the data collection days. Table 7 shows the average daily traffic volume as recorded by the Ambassador Bridge. Hourly volumes are used in the calculation of delay and are shown with the delay calculations in Tables 8 through 19.
| Station | 5/22/01 | 5/23/01 | 5/24/01 | 6/19/01 | 6/20/01 | 6/21/01 |
|---|---|---|---|---|---|---|
| OB-1* | 1,126 | 2,232 | 1,974 | 2070 | 1,842 | 1,320 |
| OB-2* | 982 | 1,287 | 1,618 | 2,194 | 943 | 2,130 |
| IB-1* | 1,114 | 2,049 | 2,169 | 2,222 | 1,965 | 1,653 |
| IB-2* | 1,418 | 2,816 | 2,677 | 1,720 | 2,455 | 1,885 |
| Total | 4,640 | 8,384 | 8,438 | 8,206 | 7,205 | 6,988 |
| Direction | 5/22/01 | 5/23/01 | 5/24/01 | 6/19/01 | 6/20/01 | 6/21/01 |
|---|---|---|---|---|---|---|
| Outbound* | 5,923 | 6,519 | 6,855 | 6,328 | 6,692 | 6,029 |
| Inbound* | 5,767 | 6,441 | 6,058 | 6,224 | 6,316 | 5,518 |
| Total | 11,690 | 12,960 | 12,913 | 12,552 | 13,008 | 11,547 |
*Note: Outbound means into Canada, Inbound means into the U.S.
Data Quality Steps
At the end of each day of data collection, the supervisor would collect the PDAs and download the data into the field laptop computer where it was stored on the hard drive. The data would be examined for any anomalies and transferred across the Internet to a secondary location for backup purposes. The OB-1 and OB-2 data would be merged together and license plates from the two locations would be "matched" using a spreadsheet developed in Microsoft Excel. As it is easy to mistake certain characters, particularly letters that looked like numbers, the license plate data was pre-processed. All 'I's were replaced with '1's; all 'O's, 'D's, and 'Q's were replaced with '0's; all 'S's were replaced with '5's; and all 'Z's were replaced with '2's. In addition, the data collectors were instructed to always use '1's for 'I's and '0's for 'O's (i.e., to use the digit, rather than the letter).
Occasionally, collectors would be unsure about a license plate and would append "QQQ" to their entry. This would typically occur when several trucks passed the collector in rapid succession or if one truck blocked the license plate of another and he or she could only manage a quick glimpse. This would allow the supervisor to search the downloaded data for a potential match by using the travel times of other trucks that were recorded in the same general time frame. During this process, the supervisor could identify the few records in which the data collector forgot to press "ENTER" after recording a license plate before recording the next one. These ten-character entries could be split into two and the time for the first interpolated from the adjacent entries if they were less than a minute or so apart.
Data post-processing also included a step to identify any anomalies in the data, including outliers. Outliers, records that indicated travel times significantly greater than typical for that time period, were most often caused by recording the license plate of a vehicle only some of the time as it made repeated trips across the border during a single day. This is because the matching algorithm uses the most recent time at the #1 position when matching to a record from a #2 location. For example, if the vehicle was recorded as it headed from Canada to the U.S. early in the morning, later returned to Canada, was missed as it re-entered the U.S. later in the day, and then recorded on its subsequent return to Canada, the #1 time from its first trip would be matched with it #1 time from the first trip (for a valid travel time) an also matched to the #2 time from its second trip (an invalid travel time). This invalid travel time would be easily identified by manual inspection of the data, aided by highlighting those travel times above a specific, but variable, threshold.
Freight Delay Analysis
The 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. Delay is measured relative to the travel time at low volume conditions, which will allow the processing time of the inspection to be accommodated outside of the measure. Estimating the average delay per truck for each hour where congestion is present and then applying the average hourly truck volume produces an estimate of total delay.
The average delay per truck for each hour is the difference between the travel time at low volume conditions and the travel time each hour. The number of open inspection booths also affects travel time and this information was recorded on all days as it changed. To determine the average travel time for each road segment, the matched license plate data in the database is used. The number of matches is noted for statistical analysis and the travel time is noted for each hour. The travel time for each truck was assigned to the hour when they passed through the primary customs inspection location as this was the only location that remained consistent throughout the data collection. It should be noted, however, that the hourly volumes are obtained from the bridge operators and are measured at the tollbooths.
The data are presented in Tables 8 through 19. The columns illustrate the key elements for estimating delay:
- No Delay 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 three-day data collection period.
- Number of Matched Vehicles – The number of vehicle observation used to estimate the travel time for each hour.
- Average Travel Time – The amount of travel time from entry to exit for trucks entering the system each hour (use the time the vehicle passes the advance point as the determinant of 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 hourly truck volume and delay per trip.
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 12:00–1:00 PM | 5.67 | 6.99 | 3 | 9.80 | 4.13 | 177 | 730.84 |
| 1:00–2:00 PM | 5.67 | 7.14 | 40 | 8.68 | 3.01 | 180 | 541.98 |
| 2:00–3:00 PM | 5.67 | 6.74 | 51 | 7.18 | 1.51 | 179 | 269.58 |
| 3:00–4:00 PM | 5.67 | 5.54 | 54 | 8.68 | 3.01 | 172 | 517.90 |
| 4:00–5:00 PM | 5.67 | 6.27 | 52 | 9.88 | 4.21 | 163 | 687.83 |
| 5:00–6:00 PM | 5.67 | 6.62 | 62 | 6.40 | 0.73 | 151 | 110.38 |
| 6:00–7:00 PM | 5.67 | 6.13 | 51 | 7.38 | 1.71 | 144 | 246.21 |
| 7:00–8:00 PM | 5.67 | 6.71 | 61 | 7.87 | 2.20 | 140 | 307.82 |
| 8:00–9:00 PM | 5.67 | 3.95 | 3 | 6.20 | 0.53 | 131 | 69.23 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 8:00–9:00 AM | 5.67 | 3.81 | 43 | 8.57 | 2.90 | 136 | 393.47 |
| 9:00–10:00 AM | 5.67 | 4.54 | 58 | 8.85 | 3.18 | 166 | 526.86 |
| 10:00–11:00 AM | 5.67 | 6.07 | 51 | 10.07 | 4.40 | 175 | 770.40 |
| 11:00–12:00 PM | 5.67 | 6.23 | 60 | 6.63 | 0.96 | 187 | 179.30 |
| 12:00–1:00 PM | 5.67 | 6.31 | 39 | 7.55 | 1.88 | 177 | 332.68 |
| 1:00–2:00 PM | 5.67 | 6.31 | 56 | 8.70 | 3.03 | 180 | 545.58 |
| 2:00–3:00 PM | 5.67 | 6.57 | 62 | 10.78 | 5.11 | 179 | 912.29 |
| 3:00–4:00 PM | 5.67 | 6.68 | 22 | 15.10 | 9.43 | 172 | 1,622.53 |
| 4:00–5:00 PM | 5.67 | 7.13 | 28 | 8.27 | 2.60 | 163 | 424.79 |
| 5:00–6:00 PM | 5.67 | 5.85 | 33 | 8.98 | 3.31 | 151 | 500.51 |
| 6:00–7:00 PM | 5.67 | 5.92 | 24 | 17.43 | 11.76 | 144 | 1,693.20 |
| 7:00–8:00 PM | 5.67 | 7.33 | 37 | 7.55 | 1.88 | 140 | 263.05 |
| 8:00–9:00 PM | 5.67 | 6.86 | 23 | 5.80 | 0.13 | 131 | 16.98 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 6:00–7:00 AM | 5.67 | 2.99 | 39 | 7.47 | 1.80 | 92 | 165.29 |
| 7:00–8:00 AM | 5.67 | 4.56 | 57 | 6.35 | 0.68 | 116 | 79.17 |
| 8:00–9:00 AM | 5.67 | 1.89 | 52 | 6.40 | 0.73 | 136 | 99.05 |
| 9:00–10:00 AM | 5.67 | 4.78 | 37 | 5.67 | 0.00 | 166 | 0.00 |
| 10:00–11:00 AM | 5.67 | 3.37 | 70 | 6.87 | 1.20 | 175 | 210.11 |
| 11:00–12:00 PM | 5.67 | 4.83 | 87 | 6.75 | 1.08 | 187 | 201.71 |
| 12:00–1:00 PM | 5.67 | 6.50 | 54 | 8.78 | 3.11 | 177 | 550.35 |
| 1:00–2:00 PM | 5.67 | 4.73 | 39 | 7.13 | 1.46 | 180 | 262.89 |
| 2:00–3:00 PM | 5.67 | 6.83 | 35 | 8.75 | 3.08 | 179 | 549.87 |
| 3:00–4:00 PM | 5.67 | 2.00 | 49 | 7.83 | 2.16 | 172 | 371.65 |
| 4:00–5:00 PM | 5.67 | 7.39 | 19 | 7.82 | 2.15 | 163 | 351.27 |
| 5:00–6:00 PM | 5.67 | 3.16 | 40 | 9.25 | 3.58 | 151 | 541.33 |
| 6:00–7:00 PM | 5.67 | 4.85 | 35 | 7.58 | 1.91 | 144 | 275.00 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 9:00–10:00 AM | 5.93 | 5.00 | 15 | 7.50 | 1.57 | 170 | 266.40 |
| 10:00–11:00 AM | 5.93 | 5.00 | 65 | 7.15 | 1.22 | 175 | 213.61 |
| 11:00–12:00 PM | 5.93 | 5.00 | 93 | 13.35 | 7.42 | 187 | 1,385.83 |
| 12:00–1:00 PM | 5.93 | 5.44 | 91 | 6.50 | 0.57 | 177 | 100.87 |
| 1:00–2:00 PM | 5.93 | 7.00 | 80 | 6.40 | 0.47 | 180 | 84.63 |
| 2:00–3:00 PM | 5.93 | 7.00 | 91 | 7.58 | 1.65 | 179 | 294.57 |
| 3:00–4:00 PM | 5.93 | 7.00 | 61 | 7.30 | 1.37 | 172 | 235.72 |
| 4:00–5:00 PM | 5.93 | 7.00 | 61 | 7.08 | 1.15 | 163 | 187.89 |
| 5:00–6:00 PM | 5.93 | 7.16 | 65 | 12.40 | 6.47 | 151 | 978.33 |
| 6:00–7:00 PM | 5.93 | 6.70 | 86 | 10.33 | 4.40 | 144 | 633.51 |
| 7:00–8:00 PM | 5.93 | 6.26 | 57 | 6.77 | 0.84 | 140 | 117.53 |
| 8:00–9:00 PM | 5.93 | 6.59 | 90 | 6.80 | 0.87 | 131 | 113.64 |
| 9:00–10:00 PM | 5.93 | 6.00 | 43 | 6.25 | 0.32 | 118 | 37.89 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 2:00–3:00 PM | 5.93 | 7.88 | 41 | 7.02 | 1.09 | 179 | 194.60 |
| 3:00–4:00 PM | 5.93 | 6.96 | 78 | 6.98 | 1.05 | 172 | 180.66 |
| 4:00–5:00 PM | 5.93 | 6.93 | 87 | 6.93 | 1.00 | 163 | 163.38 |
| 5:00–6:00 PM | 5.93 | 6.95 | 89 | 7.72 | 1.79 | 151 | 270.67 |
| 6:00–7:00 PM | 5.93 | 7.00 | 53 | 8.78 | 2.85 | 144 | 410.34 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 5:00–6:00 AM | 5.93 | 3.82 | 17 | 6.55 | 0.62 | 85 | 52.55 |
| 6:00–7:00 AM | 5.93 | 2.78 | 82 | 6.78 | 0.85 | 92 | 78.06 |
| 7:00–8:00 AM | 5.93 | 3.83 | 101 | 7.57 | 1.64 | 116 | 190.95 |
| 8:00–9:00 AM | 5.93 | 5.83 | 66 | 5.93 | 0.00 | 136 | 0.00 |
| 9:00–10:00 AM | 5.93 | 6.00 | 53 | 6.02 | 0.09 | 166 | 14.91 |
| 10:00–11:00 AM | 5.93 | 6.98 | 56 | 9.48 | 3.55 | 175 | 621.57 |
| 11:00–12:00 PM | 5.93 | 6.59 | 6 | 22.07 | 16.14 | 187 | 3,014.47 |
| 12:00–1:00 PM | 5.93 | 6.99 | 60 | 9.83 | 3.90 | 177 | 690.14 |
| 1:00–2:00 PM | 5.93 | 6.53 | 65 | 11.48 | 5.55 | 180 | 999.33 |
| 2:00–3:00 PM | 5.93 | 6.77 | 66 | 11.68 | 5.75 | 179 | 1,026.55 |
| 3:00–4:00 PM | 5.93 | 5.85 | 22 | 13.67 | 7.74 | 172 | 1,331.74 |
| 4:00–5:00 PM | 5.93 | 6.76 | 57 | 11.22 | 5.29 | 163 | 864.28 |
| 5:00–6:00 PM | 5.93 | 8.38 | 50 | 13.28 | 7.35 | 151 | 1,111.39 |
| 6:00–7:00 PM | 5.93 | 9.00 | 9 | 13.62 | 7.69 | 144 | 1,107.21 |
| Time Period | Number of "Matched" Vehicles | (d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 1:00–2:00 PM | 12.47 | 5.40 | 47 | 15.03 | 2.56 | 329 | 841.52 |
| 2:00–3:00 PM | 12.47 | 6.00 | 68 | 14.47 | 2.00 | 326 | 651.70 |
| 3:00–4:00 PM | 12.47 | 5.47 | 55 | 13.50 | 1.03 | 312 | 321.79 |
| 4:00–5:00 PM | 12.47 | 5.00 | 52 | 12.47 | 0.00 | 308 | 0.00 |
| 5:00–6:00 PM | 12.47 | 5.00 | 78 | 17.58 | 5.11 | 289 | 1,474.64 |
| 6:00–7:00 PM | 12.47 | 4.92 | 108 | 17.73 | 5.26 | 285 | 1,498.00 |
| 7:00–8:00 PM | 12.47 | 4.92 | 76 | 15.88 | 3.41 | 291 | 991.01 |
| 8:00–9:00 PM | 12.47 | 4.90 | 18 | 20.58 | 8.11 | 273 | 2,214.52 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 8:00–9:00 AM | 12.28 | 5.53 | 79 | 12.98 | 0.70 | 321 | 225.03 |
| 9:00–10:00 AM | 12.28 | 5.99 | 129 | 12.85 | 0.57 | 332 | 189.01 |
| 10:00–11:00 AM | 12.28 | 6.00 | 85 | 13.50 | 1.22 | 326 | 398.27 |
| 11:00–12:00 PM | 12.28 | 6.00 | 90 | 18.25 | 5.97 | 325 | 1,940.49 |
| 12:00–1:00 PM | 12.28 | 6.00 | 101 | 16.22 | 3.94 | 326 | 1,282.79 |
| 1:00–2:00 PM | 12.28 | 6.00 | 107 | 18.85 | 6.57 | 329 | 2,159.69 |
| 2:00–3:00 PM | 12.28 | 6.00 | 103 | 13.80 | 1.52 | 326 | 495.29 |
| 3:00–4:00 PM | 12.28 | 5.66 | 87 | 19.08 | 6.80 | 312 | 2,124.46 |
| 4:00–5:00 PM | 12.28 | 5.58 | 88 | 17.13 | 4.85 | 308 | 1,492.05 |
| 5:00–6:00 PM | 12.28 | 5.38 | 85 | 18.92 | 6.64 | 289 | 1,916.17 |
| 6:00–7:00 PM | 12.28 | 5.06 | 79 | 12.82 | 0.54 | 285 | 153.79 |
| 7:00–8:00 PM | 12.28 | 5.37 | 104 | 16.05 | 3.77 | 291 | 1,095.64 |
| 8:00–9:00 PM | 12.28 | 5.00 | 100 | 13.42 | 1.14 | 273 | 311.29 |
| 9:00–10:00 PM | 12.28 | 5.00 | 5 | 12.40 | 0.12 | 260 | 31.23 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 6:00–7:00 AM | 12.28 | 3.78 | 78 | 12.55 | 0.27 | 253 | 68.30 |
| 7:00–8:00 AM | 12.28 | 4.00 | 99 | 16.00 | 3.72 | 279 | 1,038.85 |
| 8:00–9:00 AM | 12.28 | 5.71 | 137 | 17.97 | 5.69 | 321 | 1,828.09 |
| 9:00–10:00 AM | 12.28 | 5.91 | 86 | 14.52 | 2.24 | 332 | 741.68 |
| 10:00–11:00 AM | 12.28 | 6.00 | 92 | 19.70 | 7.42 | 326 | 2,422.26 |
| 11:00–12:00 PM | 12.28 | 5.79 | 134 | 22.23 | 9.95 | 325 | 3,235.23 |
| 12:00–1:00 PM | 12.28 | 6.00 | 102 | 17.47 | 5.19 | 326 | 1,688.67 |
| 1:00–2:00 PM | 12.28 | 6.00 | 114 | 13.63 | 1.35 | 329 | 444.87 |
| 2:00–3:00 PM | 12.28 | 5.76 | 103 | 13.05 | 0.77 | 326 | 250.90 |
| 3:00–4:00 PM | 12.28 | 5.00 | 112 | 14.00 | 1.72 | 312 | 537.36 |
| 4:00–5:00 PM | 12.28 | 5.54 | 80 | 23.78 | 11.50 | 308 | 3,538.89 |
| 5:00–6:00 PM | 12.28 | 6.00 | 136 | 20.17 | 7.89 | 289 | 2,275.93 |
| 6:00–7:00 PM | 12.28 | 4.85 | 67 | 18.45 | 6.17 | 285 | 1,757.15 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 9:00–10:00 AM | 13.53 | 5.82 | 25 | 17.33 | 3.80 | 332 | 1,260.08 |
| 10:00–11:00 AM | 13.53 | 5.00 | 81 | 16.70 | 3.17 | 326 | 1,034.85 |
| 11:00–12:00 PM | 13.53 | 5.40 | 91 | 16.90 | 3.37 | 325 | 1,095.38 |
| 12:00–1:00 PM | 13.53 | 5.69 | 114 | 18.43 | 4.90 | 326 | 1,595.34 |
| 1:00–2:00 PM | 13.53 | 5.23 | 86 | 13.93 | 0.40 | 329 | 131.49 |
| 2:00–3:00 PM | 13.53 | 5.44 | 74 | 17.75 | 4.22 | 326 | 1,375.09 |
| 3:00–4:00 PM | 13.53 | 5.77 | 82 | 17.20 | 3.67 | 312 | 1,146.58 |
| 4:00–5:00 PM | 13.53 | 5.00 | 55 | 17.58 | 4.05 | 308 | 1,245.94 |
| 5:00–6:00 PM | 13.53 | 5.00 | 84 | 18.47 | 4.94 | 289 | 1,425.59 |
| 6:00–7:00 PM | 13.53 | 4.80 | 44 | 14.63 | 1.10 | 285 | 313.27 |
| 7:00–8:00 PM | 13.53 | 5.00 | 85 | 13.53 | 0.00 | 291 | 0.00 |
| 8:00–9:00 PM | 13.53 | 5.00 | 99 | 19.57 | 6.04 | 273 | 1,649.28 |
| 9:00–10:00 PM | 13.53 | 5.85 | 18 | 25.78 | 12.25 | 260 | 3,188.43 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 6:00–7:00 AM | 13.53 | 3.70 | 98 | 15.95 | 2.42 | 253 | 612.21 |
| 7:00–8:00 AM | 13.53 | 4.00 | 139 | 13.63 | 0.10 | 279 | 27.93 |
| 8:00–9:00 AM | 13.53 | 4.87 | 138 | 17.45 | 3.92 | 321 | 1,260.16 |
| 9:00–10:00 AM | 13.53 | 5.14 | 124 | 17.53 | 4.00 | 332 | 1,326.40 |
| 10:00–11:00 AM | 13.53 | 5.11 | 82 | 28.05 | 14.52 | 326 | 4,740.05 |
| 11:00–12:00 PM | 13.53 | 6.18 | 80 | 30.53 | 17.00 | 329 | 5,593.68 |
| 12:00–1:00 PM | 13.53 | 6.56 | 86 | 24.37 | 10.84 | 326 | 3,529.29 |
| 1:00–2:00 PM | 13.53 | 6.00 | 57 | 25.95 | 12.42 | 329 | 4,082.70 |
| 2:00–3:00 PM | 13.53 | 6.00 | 81 | 20.38 | 6.85 | 326 | 2,232.07 |
| 3:00–4:00 PM | 13.53 | 5.81 | 84 | 14.07 | 0.54 | 312 | 168.71 |
| 4:00–5:00 PM | 13.53 | 4.75 | 88 | 17.83 | 4.30 | 308 | 1,322.85 |
| 5:00–6:00 PM | 13.53 | 5.69 | 97 | 22.15 | 8.62 | 289 | 2,487.56 |
| 6:00–7:00 PM | 13.53 | 6.00 | 68 | 17.25 | 3.72 | 285 | 1,059.42 |
| Time Period | (a) "No Delay" Travel Time |
(b) Average No. of Open Booths |
(c) Number of "Matched" Vehicles |
(d) Average Travel Time |
(e) Delay Per Trip (d - a) |
(f) Average Traffic Volume |
(g) Total Delay (e x f) |
|---|---|---|---|---|---|---|---|
| 8:00–9:00 AM | 13.53 | 4.00 | 93 | 14.32 | 0.79 | 321 | 253.96 |
| 9:00–10:00 AM | 13.53 | 4.60 | 123 | 26.67 | 13.14 | 332 | 4,357.22 |
| 10:00–11:00 AM | 13.53 | 5.69 | 71 | 36.07 | 22.54 | 326 | 7,358.18 |
| 11:00–12:00 PM | 13.53 | 6.00 | 23 | 70.22 | 56.69 | 325 | 18,426.52 |
| 12:00–1:00 PM | 13.53 | 6.00 | 66 | 70.93 | 57.40 | 326 | 18,688.29 |
| 1:00–2:00 PM | 13.53 | 6.00 | 62 | 55.28 | 41.75 | 329 | 13,724.06 |
| 2:00–3:00 PM | 13.53 | 5.98 | 81 | 26.68 | 13.15 | 326 | 4,284.93 |
| 3:00–4:00 PM | 13.53 | 6.00 | 93 | 25.17 | 11.64 | 312 | 3,636.57 |
| 4:00–5:00 PM | 13.53 | 5.49 | 88 | 30.05 | 16.52 | 308 | 5,082.21 |
| 5:00–6:00 PM | 13.53 | 6.00 | 72 | 24.27 | 10.74 | 289 | 3,099.35 |
| 6:00–7:00 PM | 13.53 | 6.00 | 7 | 17.63 | 4.10 | 285 | 1,167.64 |
As previously mentioned, the number of open primary Customs inspection booths was also recorded.
Weather. The Monday that the data collection team arrived for the first collection period, a tornado hit Detroit that caused the police to close certain roads. Since rain was predicted during the collection period, the team utilized a third rental car, which proved to be a good decision. During both periods of data collection there was sporadic rain, generally light. It rained lightly during the first 2 days of 1st collection then it rained hard for a short period on the 3rd day. Rain reduced effectiveness of data collection by about half. With cars, three collectors were able to record safely and comfortably during heavy rain. The fourth collector, at OB-2, went into a stairwell in the Customs building with exterior access and a window where she was able to continue recording. During the 2nd collection, there was some rain each day. It rained hard the final day of collection for a two-hour period, which was the heaviest rain of either collection.
Unusual Incidents. At approximately 1:30 on June 21, the third day of the second collection, a dramatic event caused total shutdown of traffic at this border crossing for a time and delayed traffic in total for seven hours. Two men were working atop scaffolding on the U.S. side that was erected for painting a section of one of the two huge cables that supports the bridge. The scaffolding collapsed and the men were left dangling from the cable by their safety harnesses high above the road and the Detroit River. Traffic in both directions was immediately halted and vehicles on the bridge cleared.
Emergency vehicles and helicopters showed up to assist as necessary. Colleagues finally pulled the men back onto the catwalk on top of the giant cable and eventually walked them down carefully. There was total closure of traffic across the bridge for fifty minutes. Then two lanes only were open for two hours. Final clearance occurred at 8:30 P.M. Trucks that had already left the tollbooth were allowed to continue, so that the trucks that crossed during the emergency registered travel times that were not significantly different from other hours.
During this emergency, traffic backed up along Highway 3 (Huron Church Road) as far as the E.C. Row Expressway, 1.9 miles from the tollbooth, which was the fifth alternate location. The IB-1 collector relocated to each of the five alternate locations during this time. However, it was not possible for the OB-1 collector on the other side of the bridge to safely move out of position and relocate.
On one occasion during each collection (apart from the unusual total shutdown just mentioned), the supervisor observed exiting traffic (both autos and trucks) back up on the Detroit side (see figure 21). This congestion backed up in the right lane of I-75 northbound all the way to the pedestrian crossover at Ferdinand Street, one mile from the bridge entrance. Most of this exiting truck traffic continued to turn onto the bridge, although some turned off to the right prior to the bridge to get over to Fort Street or other local roads. Also, some trucks were already on the northbound Fisher Freeway at the point where I-75 exits onto it. Some of these trucks did not enter the bridge but rather turned onto I-75, I-96, or local roads. Exiting traffic backed up in the right lane of I-75 southbound all the way to Tiger Stadium, which is approximately two miles north of the Ambassador Bridge.
Figure 21. Traffic on I-75 northbound approaching Ambassador Bridge exit.
Detroit rush hour traffic seemed to be the major cause for this backup, which is unlike the queues encountered at border crossings in more rural settings. The part of this congestion that is related to the bridge infrastructure is difficult to separate from the part that is due to the city road system infrastructure. Traffic did not back up all the way across the bridge at any time during either collection.
During the first collection, a truck broke down right next to the OB-1 collector in the duty-free truck lane that curves around next to the OB-1 collector. Bridge operators closed off the affected truck tollbooth. A tow truck pulled up in front of the OB-1 collector's location and bridge operators moved plastic barricades (designed to be filled with water but empty) so that the tow truck backed up to the stalled truck. Ambassador Bridge personnel then stopped traffic and moved cones and plastic barricades to allow the tow truck to cross over from outbound traffic prior to the tollbooth into the inbound traffic lane heading into U.S. Customs (see figure 22).
Figure 22. Tow truck crossing through barricades near duty-free ramp.
