Texas Transportation Institute
The Texas A&M University System
3135 TAMU
College Station, TX 77843-3135
979-845-8829
Fax: 979-845-6008
http://tti.tamu.edu
shawn-turner@tamu.edu
March 7, 2016
TECHNICAL MEMORANDUM
TO:
Paul Czech, Minnesota Department of Transportation
FROM:
Shawn Turner, Texas Transportation Institute (TTI)
SUBJECT:
TTI Review of Selected Inrix Data in Minneapolis-St. Paul
This memo documents the key findings of a TTI review of Inrix data for selected roadway
segments in the Minneapolis-St. Paul area. The key findings and conclusions are as follows:
Comparability of Inrix Data to Other Data Sources

TTI review indicated that the Inrix speed data followed expected temporal and day-ofweek patterns and trends. Inrix speed data during the overnight hours was highly variable
(due to much smaller sample sizes) and would not be suitable for use by Mn/DOT.
However, overnight data (10 pm to 6 am) is typically not used in congestion analyses.

Comparison of Inrix speed data to the Mn/DOT fixed-point sensor data indicated that
Inrix freeway speeds were consistently slower than Mn/DOT speeds. For a two-year
average speed comparison, the mean absolute difference between average speeds was
about 5 mph during light traffic and 10 to 15 mph during the peak periods.

It is important to recognize that, at this point, we cannot say that the Mn/DOT data is
most accurate and all of this difference is due to inaccuracies in Inrix data. These
differences are most likely caused by: 1) different vehicle mix (2006-2007 Inrix data is
mostly from commercial fleet vehicles); and 2) different speed measurement techniques.

The most recent Inrix freeway speed data (January-February 2008) compared more
favorably to Mn/DOT sensor data, as the mean absolute difference was between 5 and 10
mph during the peak periods.

Comparison of Inrix arterial street speed data to Mn/DOT signal retiming data indicated
that these data were in general agreement, although no differences were quantified. There
were several methodological differences that prevent this comparison from being
conclusive: 1) the Mn/DOT data was collected over a few days, whereas the Inrix data
was collected over the entire month; 2) the Mn/DOT data consistently had fewer samples
than the Inrix data; and, 3) data aggregation in the Inrix data prevented a true “apples-toapples” comparison in the temporal and spatial dimensions.
Mobility Analysis Program
Inrix Data Sample Sizes

TTI review indicated that, on most of the routes selected by Mn/DOT, the Inrix data
sample sizes were greater than the sample sizes typically gathered through public agency
travel time data collection.

The current mix of vehicles providing speed data to Inrix appears to over-represent fleet
vehicles (such as large trucks) and under-represents passenger vehicles as they occur in
the traffic stream. The differences in speed and operating characteristics of fleet and
passenger vehicles are more distinct in stop-and-go traffic congestion, as was apparent in
several of the comparisons in this memo.

The current mix of vehicles providing speed data to Inrix leads to the highest proportion
of samples during typical workday hours, with much lower sample proportions during the
weekend and off-peak hours. However, these lower sample proportions are less critical
during these times since most congestion analyses are focused on the weekday peak
periods.

The number of Inrix data samples has significantly increased in the past two years. As
GPS is becoming more common to track vehicle locations, Inrix and other real-time
traffic information companies are aggressively pursuing these new probe vehicle data
sources.
Suitable Applications for this Data
Based upon the Inrix speed data and associated sample sizes for the Mn/DOT-selected routes, we
conclude that the most favorable applications for this type of data are those that require historical
data on an aggregate basis (e.g., a monthly or annual average, a corridor-wide performance
measure, etc.). We also conclude that the most favorable applications at this time are those that
require relative accuracy (i.e., making comparisons among routes and over time). Examples of
possible applications include but are not limited to:
 Identifying most congested routes or segments for further study and improvement;
 Ranking or prioritizing routes for funding based on average congestion levels;
 Monitoring and identifying routes with the highest increase in average congestion levels
(on monthly or annual basis);
 Using as a general indicator in before-after studies of mobility improvements; and,
 Developing performance measures on an aggregate basis.
There are certain applications that TTI cannot recommend for this type of data at this time. These
applications typically require larger sample sizes, more disaggregate data (on a daily basis), or
absolute accuracy.
 Development of reliability measures that capture day-to-day variation;
 Detailed signal retiming and synchronization studies;
 Before-after studies that require detailed data for specific time periods and locations; and,
 Real-time traffic information on certain lower functional roadway classes (those with
small sample sizes).
2
There are two additional conclusions that we have developed:

Private sector companies currently only collect and provide travel speeds, so performance
measures that require traffic volumes or flow rates will require this information from
another source, such as statewide or metro area traffic counts. Certain performance
measures do not require traffic volumes (e.g., travel time index, congestion duration,
percent of roadway miles with peak period congestion, buffer and planning time index) or
only require traffic volumes to weight performance measures in aggregated subarea or
areawide measures. Other performance measures, such as various delay measures and
throughput, do require more accurate traffic volumes.

It appears that there will be a market for the private sector provision of travel speed data
for various traveler information and telematics applications. From this, we conclude that
historical private sector data should be available to public agencies in the near term (at
some cost). However, the current companies in this market may change or be
consolidated as this industry grows. Additionally, the sample sizes behind private sector
data are predicted to increase dramatically in the next few years as GPS-enabled devices
proliferate in mobile phones and in-vehicle navigation devices. The caution associated
with this sample size increase is that before-after studies will need to carefully consider
the effects of smaller samples sizes on the accuracy of the “before” data as compared to
the “after” data.
The rest of this memo provides more details of the TTI review to support these findings and
conclusions.
INTRODUCTION
In May 2008, the Texas Transportation Institute (TTI) contracted with Inrix, Inc. to purchase a
sample of travel speed data on selected arterial street and freeway segments in the MinneapolisSt. Paul area. The data were purchased on behalf of the Minnesota Department of Transportation
( Mn/DOT) with the objective of evaluating the quality of Inrix data for mobility and reliability
monitoring and reporting purposes.
The evaluation was conducted using three strategies:
1. Visual checks of basic traffic patterns and trends;
2. Comparison with Mn/DOT freeway fixed-point sensors; and,
3. Comparison with Mn/DOT test vehicle data collected for signal retiming purposes.
BACKGROUND
Routes
Mn/DOT planning staff provided a preferred list of routes that were of primary interest. Inrix
staff matched this against their data source to ensure sufficient samples (based on their criteria).
As Figure 1 and Table 1 indicate, Inrix was able to provide data on nearly all of the roadways
3
requested by Mn/DOT. Table 1 also indicates that nearly all of the evaluated routes were based
on Mn/DOT priority and not the availability of adequate Inrix data samples.
Priority
1
2
n.a.
Table 1. Routes Requested TTI & Mn/DOT and Provided by Inrix
Route & Area Requested
Provided by Inrix
MN 65: North
MN 65: I-694 to HWY 242
US 61: Northeast
US 61: HWY 36 to HWY 96
US 61: Southeast
US 10/US 61: I-94 to I-494
MN 7: Southwest
MN 7: MN 41 to US 169
MN 55: West
MN 55: HWY 50/HWY 10 to I-494
US 169: North
US 169: HWY 130 to US 10
US 10: North
US 10/US 169: US 169 to US 169/HWY 101
MN 36: East
Substituted CO HWY 14: HWY 65 to I-35W
HWY 13: South
HWY 13: HWY 101 to HWY 77
HWY 5: Southwest
Not provided
I-394: West
Substituted I-494: US 212 to HWY 77
Figure 1. Routes on Which Inrix Provided Travel Speed Data
US 10/US 169
CO HWY 14
US 169
MN 55
MN 65
US 61
MN 7
US 10/US 61
I-494
HWY 13
4
Inrix Data
Inrix provided data from January 2006 through February 2008 in three distinct data sets:
1. 60-minute average speeds for each day of the week and month of the year
o Location (TMC code)
o Day-of-week/time (168 bins) for each month of each year
o Average speed
o Number of data samples
2. 15-minute average speeds for each day of the week
o Location (TMC code)
o Day-of-week/time (672 bins) – all months combined into a single average
o Average speed
o Number of data samples
3. 15-minute “reliability” statistics for each day of the week
o Location (TMC code)
o Day-of-week/time (672 bins)
o Average speed
o Speed percentiles: 10, 15, 25, 50, 85
o “Reliability” – frequency of time/samples below 30, 50, and 60 mph
Inrix provided a license to TTI to use this data for evaluation purposes and also granted TTI
permission to redistribute aggregate or derivative summary statistics from the speed data. The
redistribution of the original speed data provided to TTI, as well as the number of data samples,
was prohibited by the Inrix/TTI licensing agreement.
Inrix also provided TTI with a location code table that uses the RDS-TMC (Radio Data System –
Traffic Message Channel) location referencing system. This location referencing system
originated in Europe and is a de facto standard in the United States used by many of the private
traffic information companies. In North America, the TMC location codes table is maintained
and regularly updated by NAVTEQ and Tele Atlas, two of the dominant map database
companies in the market.
TMC location codes are unique numeric sequential identifiers (typically 4 to 5 digits) assigned to
intersections and interchanges that are significant for traffic messages and routing purposes. An
internal path (designated by N or P) is the directional road segment that is internal to the
identified intersection or interchange. An external path (designated by - or +) is the directional
road segment that leads up to the intersection or interchange (using local driving conventions). A
simple lookup table allows the TMC code and path to be cross-referenced to route identifier
(e.g., MN 55, US 169) and cross street limits.
The different colored circles shown in Figure 1 indicate the TMC code locations for the routes on
which Inrix provided historical travel speed data. Figure 2 shows a zoomed view for one route,
MN 7 (part of the I-494 route also can be seen in the bottom right corner). As the figure
5
indicates, the selection and spacing of TMC code locations varies based on the road network.
The assignment of TMC codes to specific intersections or interchanges is a decision made by
NAVTEQ and Tele Atlas based on their significance for traffic messages and routing purposes.
The typical length of roadway (i.e., TMC path) for which travel speed data was provided ranged
from 0.1 to 4.75 miles, with an average length of 1.1 miles. For parts of the evaluation, these
original link definitions were used to facilitate comparisons with Mn/DOT freeway sensor data.
In other parts of the evaluation, these original links were combined to produce longer roadway
segments that ranged from 1.5 to 9.7 miles (see Table 2). Summary travel speed statistics were
then calculated for these longer roadway segments and are shown in later parts of this report.
Figure 2. Example of TMC Code Locations on MN 7
6
Table 2. Combined Roadway Segments Used in Some Parts of the Evaluation
Route and Limits
MN 65 NB: I-694 to US 10
MN 65 NB: US 10 to HWY 242
MN 65 SB: HWY 242 to US 10
MN 65 SB: US 10 to I-694
US 61 NB: HWY 36 to I-694
US 61 NB: I-694 to HWY 96
US 61 SB: HWY 96 to I-694
US 61 SB: I-694 to HWY 36
US 10/US 61 EB: I-94 to I-494
US 10/US 61 WB: I-494 to I-94
MN 7 EB: MN 41 to I-494
MN 7 EB: I-494 to US 169
MN 7 WB: US 169 to I-494
MN 7 WB: I-494 to MN 41
HWY 55 EB: HWY 50/HWY 10 (Rockford) to CR 116
HWY 55 EB: CR 116 to I-494
HWY 55 WB: I-494 to CR 116
HWY 55 WB: CR 116 to HWY 50/HWY 10 (Rockford)
US 169 NB: HWY 130 to HWY 610
US 169 NB: HWY 610 to US 10
US 169 SB: US 10 to HWY 610
US 169 SB: HWY 610 to HWY 130
US 10/US 169 EB: 169/HWY 101 to CR-56
US 10/US 169 EB: CR-56 to US 169
US 10/US 169 WB: US 169 to CR-56
US 10/US 169 WB: CR-56 to US 169/HWY 101
HWY 13 NB: HWY 101 to I-35W
HWY 13 NB: I-35W to HWY 77
HWY 13 SB: HWY 77 to I-35W
HWY 13 SB: I-35W to HWY 101
I-494 EB: US 212 to US 169
I-494 EB: US 169 to HWY 100
I-494 EB: HWY 100 to I-35W
I-494 EB: I-35W to HWY 77
I-494 WB: HWY 77 to I-35W
I-494 WB: I-35W to HWY 100
I-494 WB: HWY 100 to US 169
I-494 WB: US 169 to US 212
CO HWY 14 EB: HWY 65 to CR-17
CO HWY 14 EB: CR-17 to I-35W
CO HWY 14 WB: I-35W to CR-17
CO HWY 14 WB: CR-17 to HWY 65
7
Length
(miles)
4.7
4.3
4.3
4.7
1.9
3.2
3.2
1.9
4.8
4.8
6.8
2.6
2.6
6.8
9.7
4.9
4.9
9.7
2.8
5.4
5.4
2.8
6.7
3.5
3.5
6.7
4.5
4.2
4.2
4.5
1.5
2.2
2.6
2.5
2.5
2.6
2.2
1.5
3.4
4.4
3.4
4.4
Speed Limit
Range (mph)
40 to 55
55 to 60
55 to 60
40 to 55
50
50
50
50
45 to 60
45 to 60
50 to 55
45 to 55
45 to 55
50 to 55
50 to 55
55 to 55
55 to 55
45 to 55
55
30 to 55
30 to 55
55
60 to 65
60
60
60 to 65
45 to 55
50 to 55
50 to 55
55
60
60
60
60
60
60
60
60
50 to 55
50 to 55
50 to 55
50 to 55
EVALUATION FINDINGS
In an ideal evaluation scenario with no budgetary constraints, extensive “ground truth” travel
speeds would be obtained on the evaluation routes to determine the error associated with Inrix
travel speeds. In this case, the collection of “ground truth” travel times for long periods of time
(two years in this case) is simply not feasible. Therefore, TTI researchers assessed the quality of
the Inrix data using three strategies:
1. Perform visual checks of basic traffic patterns and trends in Inrix data;
2. Compare Inrix data with Mn/DOT freeway fixed-point sensor data; and,
3. Compare Inrix data with Mn/DOT test vehicle data collected for signal retiming
purposes.
The findings from these three strategies are described in the following sections.
Visual Checks of Traffic Patterns and Trends
Basic time-of-day speed profile charts were prepared for the two distinct average speed data sets:
1. 15-minute average speeds (all months combined); and,
2. 60-minute average speeds (month-by-month).
Figures 3 and 4 show examples of the 15-minute average speed profiles on which all travel
speeds from January 2006 through February 2008 are combined. It should be noted that Inrix
provided separate averages for each day of the week. Because the differences between the five
weekdays were relatively minor, TTI combined the five weekday values into a single weekday
average. Appendix A contains similar 15-minute average speed charts for all 42 roadway
segments as defined in Table 2.
Figures 5 and 6 show examples of the 60-minute average speed profiles on which all travel
speeds were reported on a month-by-month basis (year 2007 shown). It should be noted that
Inrix provided separate averages for each day of the week and each month of the year from
January 2006 through February 2008. Because the differences between the five weekdays were
relatively minor, TTI combined the five weekday values into a single weekday average.
Appendix B contains similar 60-minute average speed charts for all 42 roadway segments as
defined in Table 2.
8
Figure 3. Example of 15-Minute Average Speed Profile, US 169 NB
US 169 NB: HWY 130 to HWY 610
70
15-Minute Average Weekday Speeds, Jan 2006 through Feb 2008
Average Corridor Speed (mph)
60
Posted speed limit is 55 mph
50
40
30
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM 12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
Figure 4. Example of 15-Minute Average Speed Profile, US 169 SB
US 169 SB: HWY 610 to HWY 130
70
15-Minute Average Weekday Speeds, Jan 2006 through Feb 2008
Average Corridor Speed (mph)
60
Posted speed limit is 55 mph
50
40
30
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM 12 PM
2 PM
4 PM
Time of Average Weekday
9
6 PM
8 PM
10 PM
Figure 5. Example of 60-Minute Average Monthly Speed Profile for 2007, US 169 NB
US 169 NB: HWY 130 to HWY 610
70
Hourly Average Weekday Speeds by Month in 2007
60
Average Corridor Speed (mph)
Posted speed limit is 55 mph
50
2007 - 1
2007 - 2
2007 - 3
40
2007 - 4
2007 - 5
2007 - 6
30
2007 - 7
2007 - 8
2007 - 9
20
2007 - 10
2007 - 11
2007 - 12
10
0
12 AM 2 AM
4 AM
6 AM
8 AM 10 AM 12 PM 2 PM
4 PM
6 PM
8 PM 10 PM
Time of Average Weekday
Figure 6. Example of 60-Minute Average Monthly Speed Profiles for 2007, US 169 SB
US 169 SB: HWY 610 to HWY 130
70
Hourly Average Weekday Speeds by Month in 2007
60
Average Corridor Speed (mph)
Posted speed limit is 55 mph
50
2007 - 1
2007 - 2
2007 - 3
40
2007 - 4
2007 - 5
2007 - 6
30
2007 - 7
2007 - 8
2007 - 9
20
2007 - 10
2007 - 11
2007 - 12
10
0
12 AM 2 AM
4 AM
6 AM
8 AM 10 AM 12 PM 2 PM
4 PM
Time of Average Weekday
10
6 PM
8 PM 10 PM
Comparison with Mn/DOT Freeway Fixed-Point Sensor Data
The second strategy used by TTI to evaluate the quality of Inrix data was to compare it with
speeds collected by Mn/DOT’s freeway fixed-point sensors. The underlying speed measurement
technique for each data source is different, as the Mn/DOT sensor is fixed and measures spot
speed at one location, whereas the Inrix data are mostly spot speeds collected from various
locations near the Mn/DOT fixed-point sensor. Another difference is that the Mn/DOT sensors
measure the spot speeds of all vehicles it detects, whereas Inrix data includes a limited sample of
vehicles in the traffic stream. Notwithstanding this difference in measurement technique, a
comparison was useful to see how similar the data sources were.
The comparison was performed at numerous locations along I-494 (Figure 7). Average speeds
along the entire I-494 segment were first compared (Figures 8 and 9). Next, individual Mn/DOT
sensor locations were compared to the nearest Inrix link data and the error results were
aggregated along the entire I-494 segment (Figures 10 and 11).
Figure 7. Comparison of Inrix Data to Mn/DOT Fixed-Point Sensors
Note: Inrix TMC code locations = small red circles
Mn/DOT fixed-point sensors = large blue circles
These comparisons indicated that Inrix speeds were typically 5 to 10 mph slower than the
Mn/DOT speeds. The differences were greatest during the peak periods, when speeds were the
slowest. We hypothesize that most of this difference is due to:
1. Vehicle bias – We believe that Inrix speeds are mostly collected from fleet vehicles
(large trucks) that have different operating characteristics than passenger vehicles in
traffic congestion. For example, a previous TTI study in Houston showed that truck
speeds were about 4% to 8% (2 to 4 mph) slower than passenger vehicle speeds;
2. Different measurement techniques – Mn/DOT sensor speeds are measured at fixed
location, whereas Inrix speeds are measured at various random locations on the same
link; and,
3. Sampling – Inrix speeds are only collected from a sample of the vehicle traffic, whereas
Mn/DOT sensors collect speeds from every vehicle.
In comparing the most recently available Inrix data from January and February 2008 (Figure 9),
it appears that with the increased data samples in recent months (see later sections of this memo),
the differences between Inrix and Mn/DOT speeds have decreased.
11
Figure 8.Average Speed Comparison across Two Years, I-494
Comparison of Average Weekday Speeds along I-494
(15-Minute Intervals, Jan 2006 through Feb 2008)
70
Average Speed (mph)
60
50
40
30
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM 12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
MnDOT Detectors
Inrix Probes
Mean Absolute Difference
Figure 9. Average Speed Comparison in Jan-Feb 2008, I-494
Comparison of Average Weekday Speeds along I-494
(60-Minute Intervals, Jan-Feb 2008)
70
Average Speed (mph)
60
50
40
30
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
12 PM
2 PM
4 PM
6 PM
Time of Average Weekday
MnDOT Detectors
Inrix Probes
12
Mean Absolute Difference
8 PM
10 PM
Figure 10. Speed Error at Individual Locations across Two Years, I-494
Distribution of Average Speed Differences along I-494
(15-Minute Intervals, Jan 2006 through Feb 2008)
600
Inrix speeds slower than MnDOT speeds
Inrix speeds faster than MnDOT speeds
500
Frequency
400
300
200
100
0
-50
-40
-30
-20
-10
0
10
20
30
40
50
Difference (MnDOT - Inrix)
Figure 11. Speed Error at Individual Locations in Jan-Feb 2008, I-494
Distribution of Average Speed Differences along I-494
(60-Minute Intervals, Jan-Feb 2008)
120
Inrix speeds faster than MnDOT speeds
Inrix speeds slower than MnDOT speeds
100
Frequency
80
60
40
20
0
-50
-40
-30
-20
-10
0
10
Difference (MnDOT - Inrix)
13
20
30
40
50
Comparison with Mn/DOT Test Vehicle Data
The third strategy used by TTI to evaluate the quality of Inrix data was to compare it with
“floating car” speeds collected by Mn/DOT contractors for signal retiming purposes. As with the
previous comparison, the underlying speed measurement technique for each data source is
different, as the Mn/DOT floating car measure space mean speed (average speed over a
distance), whereas the Inrix data are mostly spot speeds collected from various locations over a
similar road link. Another difference is that the Mn/DOT signal retiming data was collected at
limited times during the day, and only on several days. The Inrix data is collected on a routine
basis for every day of the year. Unfortunately, the Mn/DOT signal retiming data was the only
travel speed data that was readily available on the arterial streets.
Figure 12 shows the two arterial streets on which comparisons were made: MN, 55 and MN 65.
As with the I-494 segments, speed comparisons were made on an aggregated basis where the link
definitions for measured speeds matched. An attempt was also made to match the month of data
collection, although this was not possible in every case.
Figure 12. Comparison of Inrix Data to Mn/DOT Signal Retiming Data
2 Comparison Corridors
MN 55
MN 65
18
Figures 13 through 16 show the results of this comparison. Note that in many time periods, the
average speeds from the Mn/DOT were based on fewer speed data samples than the Inrix data.
From these comparisons, one is unable to determine which speed data is more accurate, only
how the two speed data sources compare to one another.
14
Figure 13. Comparison of Speeds along MN 55 Eastbound
Comparison of Average Weekday Speeds along TH 55 EB
70
Hourly Average Weekday Speeds by Month in May 2007
60
Posted speed limit is 55 mph
Average Speed (mph)
50
MnDOT Average
40
30
Inrix Monthly Average
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
Figure 14. Comparison of Speeds along MN 55 Westbound
Comparison of Average Weekday Speeds along TH 55 WB
70
Hourly Average Weekday Speeds by Month in May 2007
60
Posted speed limit is 55 mph
Average Speed (mph)
50
MnDOT Average
40
Inrix Monthly Average
30
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
12 PM
2 PM
Time of Average Weekday
15
4 PM
6 PM
8 PM
10 PM
Figure 15. Comparison of Speeds along MN 65 Northbound
Comparison of Average Weekday Speeds along MN 65 NB
70
Hourly Average Weekday Speeds
60
Average Speed (mph)
50
MnDOT Average
(Aug-Sep 2003)
40
30
Inrix Average
(Aug-Sep 2006,2007)
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
Figure 16. Comparison of Speeds along MN 65 Southbound
Comparison of Average Weekday Speeds along MN 65 SB
70
Hourly Average Weekday Speeds
60
Average Speed (mph)
50
MnDOT Average
(Aug-Sep 2003)
40
30
Inrix Average
(Aug-Sep 2006,2007)
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
12 PM
2 PM
Time of Average Weekday
16
4 PM
6 PM
8 PM
10 PM
Evaluation of Data Sample Sizes
As indicated previously, Inrix did provide number of data samples associated with the average
speeds. However, the number of data samples is protected by the Inrix-TTI nondisclosure
agreement. Based on our analysis of the confidential information regarding sample sizes, we
developed a qualitative assessment for the routes that were evaluated in this effort. The
qualitative assessment (see Table 3) is based on these three factors:
1. Absolute number of data samples;
2. Relative number of data samples as compared to current agency practice; and,
3. Comparability of Inrix data to Mn/DOT data and expected patterns/trends.
Table 3. Qualitative Assessment Based on Evaluation Criteria
Route
Evaluation Criteria
Absolute samples
Relative samples
Comparability
Evaluated
US 10/US 169
1
1
2
HWY 13
1
1
2
I-494
1
2
2
MN 65
2
2
2
US 10/US 61
2
2
2
MN 55
2
2
2
US 169
2
2
2
CO HWY 14
2
2
3
US 61
3
3
2
MN 7
3
3
3
Note: 1=high (most desirable); 2=moderate; 3=low (least desirable)
Composite Score
4
4
5
6
6
6
6
7
8
9
At TTI’s request, Inrix did provide permission to TTI to release the general patterns and trends
associated with the speed data samples. These are shown in Figures 17 through 22.
Of particular note is the increase of Inrix data samples from January 2006 to January 2008. By
comparing Figure 19 to Figure 20 (both charts have the same y-axis scale), one can see that the
average number of data samples on each route has at least doubled on most routes, and tripled or
quadrupled on some routes. An even more pronounced increase in data samples can be seen by
comparing Figure 21 to Figure 22 (both charts have the same y-axis scale). In these charts, nearly
all of the average weekday samples have quadrupled between 2006 and 2008.
17
Figure 17. Time-of-Day Trends in 15-Minute Data Samples, By Route
Total Number of 15-Minute Samples in 26 Months
Averaged across all links (both directions) on each corridor
300
Number of Speed Data Samples
250
US 10/US 169
200
I-494
HWY 13
US 169
150
MN 65
US 10/US 61
HWY 14
100
HWY 55
MN 7
US 61
50
0
12 AM 2 AM 4 AM 6 AM 8 AM 10 AM 12 PM 2 PM 4 PM 6 PM 8 PM 10 PM
Time of Average Weekday
Figure 18. Time-of-Day Trends in 15-Minute Data Samples, By Day of Week
Total Number of 15-Minute Samples in 26 Months
Averaged across all corridors for each day of the week
100
Number of Speed Data Samples
90
80
70
60
50
40
30
20
10
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM 12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
Sunday
Monday
Tuesday
Wednesday
18
Thursday
Friday
Saturday
Figure 19. January 2006 Time-of-Day Trends in 60-Minute Data Samples, By Route
Total Number of 60-Minute Samples in January 2006
Averaged across all links (both directions) on each corridor
16
Number of Speed Data Samples
14
12
US 10/US 169
10
HWY 13
US 169
8
MN 65
I-494
HWY 14
6
HWY 55
MN 7
4
US 61
2
0
12 AM 2 AM 4 AM 6 AM 8 AM 10 AM 12 PM 2 PM 4 PM 6 PM 8 PM 10 PM
Time of Average Weekday
Figure 20. January 2008 Time-of-Day Trends in 60-Minute Data Samples, By Route
Total Number of 60-Minute Samples in January 2008
Averaged across all links (both directions) for each day of the week
16
Number of Speed Data Samples
14
12
US 10/US 169
HWY 13
10
I-494
US 10/US 61
8
MN 65
HWY 14
6
MN 7
HWY 55
4
US 169
US 61
2
0
12 AM 2 AM 4 AM 6 AM 8 AM 10 AM 12 PM 2 PM 4 PM 6 PM 8 PM 10 PM
Time of Average Weekday
19
Figure 21. January 2006 Time-of-Day Trends in 60-Minute Data Samples, By Day of Week
Total Number of 60-Minute Samples in January 2006
Averaged across all links (both directions) on each corridor
16
Number of Speed Data Samples
14
12
10
8
6
4
2
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM 12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Figure 22. January 2008 Time-of-Day Trends in 60-Minute Data Samples, By Day of Week
Total Number of 60-Minute Samples in January 2008
Averaged across all links (both directions) for each day of the week
7
Number of Speed Data Samples
6
5
4
3
2
1
0
12 AM
2 AM
4 AM
6 AM
8 AM
10 AM
12 PM
2 PM
4 PM
6 PM
8 PM
10 PM
Time of Average Weekday
Sunday
Monday
Tuesday
Wednesday
20
Thursday
Friday
Saturday
APPENDIX
The appendix contains time-of-day speed profiles for the following conditions:

15-minute average speeds – Average weekday speeds from January 2006 through
February 2008, all months combined.

60-minute average speeds – Average weekday speeds from January 2007 through
December 2007, each month shown as separate trend line.
21