Office of Operations Freight Management and Operations

Evaluation of Travel Time Methods to Support Mobility Performance Monitoring:
Ambassador Bridge (Page 3 of 5)

Data Collection Details

Both the Canada Bridge and Tunnel Operator's Association and Ambassador Bridge provided border crossing statistical data. This data was evaluated for an assessment of the variability in travel conditions at the Ambassador Bridge. The goal of this analysis process is to obtain statistically useful data with as few data collection days as possible. In order to customize the data collection activities at the Ambassador Bridge, the following steps were conducted:

  • Define significant "seasonal" variations,
  • Define significantly different days of the week,
  • Identify traffic streams that experience significantly different conditions, and
  • Estimate the number of days needed for the data collection survey.

As shown in Table 3, there is some variation in the commercial traffic by month, which was most pronounced in 2000. Due to project constraints, data collection needed to occur between late May and early September 2001. From Table 3, the two months with the greatest average volumes during this data collection window were May and June.

Table 3. Monthly Traffic Distribution of Commercial Vehicles
Month 1998 1999 2000 1998-2000 Average
January 231,614 252,146 289,122 772,882
February 233,982 267,917 300,190 802,089
March 262,051 310,562 335,595 908,208
April 252,893 284,676 287,856 825,425
May 253,182 291,085 315,227 859,494
June 252,175 312,437 310,376 874,988
July 196,751 234,738 224,327 655,816
August 242,034 306,629 310,658 859,321
September 258,811 298,182 293,269 850,262
October 274,318 302,598 309,571 886,487
November 261,163 300,406 287,644 849,213
December 274,318 266,775 222,275 763,368
Total 2,995,290 3,430,150 3,488,110 9,907,551

Source: United States – Canada Bridge and Tunnel Operator's Association Traffic Reports

Tables 4 and 5 show that there is a significant difference in commercial traffic between weekdays and weekends and, further, there is a significant difference between Monday and Friday and the three mid-week days. Weekend traffic is 15 percent of typical weekday traffic and Monday/Friday traffic is 59 percent of typical Tuesday/Wednesday/Thursday traffic. In general, it was noted that outbound traffic increased from Tuesday through Thursday and inbound traffic decreased from Tuesday through Thursday. It was determined that collecting data three days of data, from Tuesday through Thursday, would provide an adequate number of data samples to represent "typical" conditions.

Table 4. Sample Month – Daily Traffic Distribution of Commercial Vehicles for June 2001
Day Day of Week Outbound Inbound
1 Friday 6,855 4,925
2 Saturday 3,398 2,301
3 Sunday 1562 2,541
4 Monday 5,373 6,020
5 Tuesday 6493 6,399
6 Wednesday 6,498 6,289
7 Thursday 7,042 5,863
8 Friday 6,589 4,700
9 Saturday 3,222 2,271
10 Sunday 1,421 2,280
11 Monday 4,928 5,725
12 Tuesday 6,242 6,115
13 Wednesday 6,432 6,069
14 Thursday 6,776 5,713
15 Friday 6,372 4,543
16 Saturday 3,145 2,155
17 Sunday 1,379 2,261
18 Monday 5,039 5,823
19 Tuesday 6,328 6,224
20 Wednesday 6,692 6,316
21 Thursday 6,029 5,518
22 Friday 6,514 4,683
23 Saturday 3,257 2,281
24 Sunday 1,419 2,318
25 Monday 4,993 5,473
26 Tuesday 6,149 5,839
27 Wednesday 6,210 5,837
28 Thursday 6,617 5,620
29 Friday 5,827 4,070
30 Saturday 2,451 1,823
Total empty cell 151,252 137,995

Source: Ambassador Bridge

Table 5. Averages for Sample Month – Daily Traffic Distribution of Export Commercial Vehicles for June 2001
Day of Week Week 1 Week 2 Week 3 Week 4 Week 5 Average
Sunday empty cell 4,103 3,701 3,640 3,437 3,720
Monday empty cell 11,393 10,653 10,862 10,466 10,844
Tuesday empty cell 12,892 12,357 12,552 11,988 12,447
Wednesday empty cell 12,787 12,501 13,008 12,047 12,586
Thursday empty cell 12,905 12,489 11,547 12,237 12,295
Friday 11,780 11,289 10,915 11,197 9,897 11,016
Saturday 5,699 5,493 5,300 5,538 4,274 5,261

Source: Ambassador Bridge

From discussions with the Ambassador Bridge, it was learned that backups typically did not occur on the U.S. side and, when they did, they did not grow very long. However, on the Canadian side, backups occurred more frequently and could stretch for several miles along Highway 3. Ambassador Bridge personnel on the Canadian side also related that traffic heading for the U.S. picks up around 5:00 A.M. It is busy until around 9:00 A.M. to 10:00 A.M., then plateaus until around 3:00 P.M. From 3:00 to 6:00 P.M., traffic falls off.

Data Collection Procedures

The data collection stations selected for the crossing were chosen because of the particular actions that occur at each site. Segments defined by the data collection stations were used to determine the commercial vehicle travel times and freight delay. As illustrated in Figures 3-6, the data collection sites could be located at:

  • An advance station located upstream of the commercial vehicle queue – OB-1 and IB-2.
  • The import station (primary inspection booths before detailed, or secondary, inspection) – OB-2 and IB-2.

The OB-1 collector was positioned about 50 yards upstream from the tollbooths at a point where all trucks can be seen entering the bridge (see figure 11). In this position, the collector could see all of the trucks entering from Porter Street (see figure 12), from the I-96 feeder road (see figure 13), from Fisher Freeway as they turned sharp right, and from the duty-free area making a sharp turn on the other side of a barricade from the main truck traffic (see figure 14). The OB-1 collector did not move out in response to a queue during either collection period. Had the collector done so, the process is one that requires care and alertness for safety's sake. In order to stay on the U.S. side from the Outbound 1 observation site chosen, the collector has to carefully make his way onto the service road, crossing the flow of trucks that are making a sharp turn to enter the Ambassador Bridge, in order to get to the left lane and turn left.

Photo of Outbound 1 data collection site just upstream from tollbooths on Detroit side
Figure 11. Outbound 1 data collection site just upstream from tollbooths on Detroit side.

Photo of Outbound traffic crossing the Porter Street overpass above I-75
Figure 12. Outbound traffic crossing the Porter Street overpass above I-75.

Photo of Outbound traffic exiting from I-96 feeder road onto Ambassador Bridge, Detroit side
Figure 13. Outbound traffic exiting from I-96 feeder road onto Ambassador Bridge, Detroit side.

Photo of outbound trucks departing main duty-free store
Figure 14. Outbound trucks depart main duty free store separated from main traffic and turn right.

At that point, if moving out to get ahead of a queue the collector must either: (1) turn left onto Porter Street and left again after crossing I-75 onto the one-way street (Fisher Freeway southbound) that parallels I-75; (2) go straight coming out from the bridge and bear left to enter I-75N; or go straight coming out from the bridge and bear right onto a service road, after which there is an opportunity to cross over I-75 on Vernor Street and left again on Fisher Freeway to access the exit ramp off I-75 southbound. In the vicinity of the bridge, the crossover streets above I-75 south of Porter Street are Howard Street and West Grand, and north of Porter street is Vernor.

The OB-2 collector was about 50 yards downstream from primary, next to the flagpoles beside the Canadian Customs building (see figure 15), which gave good alignment with the axes of the tollbooths with exiting trucks. The IB-2 collector was on the left about 50 yards downstream from primary.

Photo of Outbound 2 data collector beside Canadian Customs building
Figure 15. Outbound 2 data collector beside Canadian Customs building.

The IB-2 collector was located where the ramp comes up from Wyandotte Street, across from the duty free area. In this position (see figure 16), the IB-2 collector can record trucks in all lanes of the directional flow: the mainstream of truck traffic on Huron Church Road (figure 17), trucks coming up the entrance ramp from Wyandotte Street, and trucks exiting the commercial vehicle duty free parking area. When the IB-2 collector had to move out and follow the queue, there was a way he/she could exit through an adjacent part of the toll facility that is ordinarily not open except during times of special events or other heavy traffic. The way out is through a parking lot and left onto Wyandotte Street W. From there, the collector can cross under the bridge and turn left to merge onto Huron Church Road southbound, which is the best route to get upstream to the head of the queue.

Photo of Inbound 1 data collector at right with Wyandotte Street tollbooths in background
Figure 16. Inbound 1 data collector at right with Wyandotte Street tollbooths in background.

Photo of Inbound 1 data collection site. Trucks shown just departed Huron Church Road.
Figure 17. Inbound 1 data collection site. Trucks shown just departed Huron Church Road.

At the Ambassador Bridge, other than an unusual event on the third day, there was no time at which trucks backed up all the way across the bridge in either direction. Data collectors in the outbound direction did not relocate due to an increasing queue length, but the collectors located in the inbound direction did have to move. Five alternate locations along Highway 3 (Huron Church Road) were chosen, depending on the conditions at the time. Any distances given are from the initial location. Of course, it was easiest to record data at that initial location close to the tollbooths where trucks move slowly approaching the bridge to depart Canada.

Two alternate locations were in generally close proximity to the original location – walking distance for the collector. The first of these was 0.15 mile upstream from the original location, where autos and trucks split as they enter the duty free and tollbooth areas. The second alternate location was 0.3 mile upstream, where the railroad track crossed the road beside an intersection with a traffic light.

The third alternate location was 0.65 mile, at the Assumption School at the intersection of Girardot Street. The fourth was at 0.95 mile, at one corner of University Mall where Tecumseh road West intersects. The final alternate location was at a Travelodge motel 2.25 miles upstream, just before Highway 3 intersects with E.C. Row Expressway (see figures 18 and 19). Of course, all alternate locations were on the same side (the east side) of Huron Church Road. Even at the intersections, trucks would pass at highway speeds and would often use both lanes, reducing the number of vehicles that could be effectively recorded.

Photo of farthest Inbound 1 data collection queue site
Figure 18. Site of farthest Inbound 1 data collection queue site (5th alternate station, approximately 2 miles from regular IB-2 station).

Photo of Inbound 1 data collector at 5th alternate location
Figure 19. Inbound 1 data collector at 5th alternate location.

Data collection was conducted by recording commercial vehicle license plates as vehicles crossed fixed points within the data collection sites. Survey individuals or teams, were placed at each of the four data collection sites to record commercial vehicle license plate data. Figures 8-10 contain diagrams of the facilities on both sides of the border, including station locations and major points of inspection.

Collectors at these locations would record the last five characters of the front, lower-left license plate of as many trucks as possible that passed their location. When trucking firms register many vehicles at once, they often get assigned sequential license plate numbers. Using the last five characters helps to ensure that as different trucks operated by the same firm travel across the bridge that they are uniquely identified. License plate information was entered into handheld computers: Palm m100 PDAs for the first collection and Handspring Visor PDAs for the second collection, both having a special application designed for this project. Each entry was time-stamped with the current date and time. Prior to each day's collection, all PDAs were synchronized to the same time. Prior experience indicated that recording the entire license plate was too time consuming and that entering only the last four characters did not provide adequate distinction between different vehicles, so the project team chose to record the last five characters.

Typically, the queue of trucks crossing the border would not extend beyond the bridge plaza. However, on occasion the queue would extend onto the highway system. When this occurred, the data collector at the #1 location would have to move further from the bridge to a point beyond the end of the queue. In this way, they could continue to record trucks before they began their wait at the end of the line. When this or any other event of interest occurred, the collectors would use an "EVENT" feature of the PDA software to record it.

For each #1 location, the supervisor would record the distance from any data collection point other than the original position (which would be in the bridge plaza). During post-processing, the data from all locations nearer to the bridge than the farthest location would be adjusted to include the additional travel time from the farthest location to the original location. The travel time would be computed at free-flow speeds, since there would have been no queue at the times that the data were collected at these closer locations. In this way, the data all would appear to be collected from the same location, the one most distant from the bridge. This method does not factor in delays caused by traffic lights, however. In the case of the Ambassador Bridge collection, there were a total of five additional data collection points that were utilized during the second data collection period, some of which extended beyond intersections with traffic lights.

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