2. Utah Intersection Safety Overview

2.1 General Discussion

As discussed in Section 1, the CDDS provided motor vehicle crash data; 10-year (1994-2003) and three-year (2001-2003) study periods were used. National crash statistics reveal the seriousness of intersection safety concerns. In 2003, for example, there were an estimated 6,328,000 motor vehicle crashes in the United States. A total of 2,567,000 crashes (40.6 percent) were at intersections or were "intersection-related." Of the 2,567,000 intersection crashes, 64.8 percent resulted in property damage only, 34.8 percent resulted in injuries, and 0.4 percent were fatal (Traffic Safety Facts 2003). Similar summary statistics for Utah were not available, but a total of 53,370 motor vehicle crashes occurred statewide in 2002 (the latest year for which cumulative data were available). If 40 percent of the crashes occurred at or near intersections, then there were about 21,500 such incidents. Of that year's 276 fatal crashes, an estimated 85 occurred at or near intersections. From 1993 to 2002 (10-year period), a total of 555,176 crashes occurred in the state; an estimated 225,400 of these occurred at or near intersections. From 2000 to 2002 (3-year period), a total of 159,225 crashes occurred; about 64,600 of these occurred at or near intersections. Although these statistics are inexact, they suggest the magnitude of the intersection safety problem in Utah.

Intersection crash statistics were tabulated for the two aforementioned study periods for the seven geographical areas summarized in Table 2.1. Year 2003 vehicle-miles of travel (VMT) levels were roughly proportional to year 2003 populations in the UDOT regions, with additional variation related to economic, tourism and other activities. Intersection safety problems are expected to be related to travel amounts. For example, UDOT Region 2, with 25.8 million DVMT in 2003 (39.3 percent of the state's DVMT) should feature the greatest intersection safety concerns of all UDOT regions. Figure 2.1 shows the locations of the UDOT regions and districts.

Table 2.1  Utah Geographical Regions

2.2 Statewide Intersection Crash Statistics

The research team ranked intersections according to two measures of safety performance: the total number of crashes occurring during a given study period, and the total crash severity score for a given study period. A third measure, crash rate, was used to examine intersections between two state routes only. The crash severity score was determined based on the medical outcome of each crash, as stated in the corresponding police accident report (PAR) and as recorded in the CDDS. The scores were based on the cost associated with each outcome, as estimated in a 1994 technical advisory (FHWA 1994). In that advisory, the following figures were proposed as a combination of the costs of property damage: medical intervention, lost earnings, lost household production, emergency services, travel delay, vocational rehabilitation, workplace losses, administrative procedures, legal matters, pain, and lost quality of life.

Figure 2.1. Utah Department of Transportation Regions and Districts

The injury categories were based on the K-B-B-C scale. The analogous CDDS categories are provided in parentheses, along with the average cost associated with each:

• Fatality (fatality): $2,600,000
• Incapacitating (broken bones or bleeding wounds): $180,000
• Evident (bruises and abrasions): $36,000
• Possible (possible injury): $19,000
• Property damage only (no injury): $2,000

These costs were rounded to the nearest "tens" unit to simplify the scores. The following scores were produced. As indicated, one fatal crash is ten times as costly as a crash resulting in broken bones or bleeding wounds:

• No injury: 0.1
• Possible injury: 1
• Bruises and abrasions: 10
• Broken bones or bleeding wounds: 100
• Fatality: 1,000

Fifty-deep statewide rankings were produced for each of the following:

• 1994-2003 crashes, based on the total number of crashes (Table 2.2)
• 2001-2003 crashes, based on the total number of crashes (Table 2.3)
• 1994-2003 crashes, based on the total crash severity score (Table 2.4)
• 2001-2003 crashes, based on the total crash severity score (Table 2.5)

The intersections ranked based on the total number of crashes experienced are listed in Tables 2.2 (1994-2003) and 2.3 (2001-2003). The intersection having the most crashes during both the 10-year and three-year study periods was Bangerter Highway (SR 154) at 5400 South (SR 173) in Taylorsville. This intersection had 949 collisions between 1994 and 2003, and 296 between 2001 and 2003, or an average of about 95 per year. For both study periods, the three intersections having the most crash activity were all in Taylorsville. On the 10-year list, 17 of the intersections are in Region 1, 29 are in Region 2, 4 are in Region 3, and none are in Region 4. On the 3-year list, 20 of the intersections are in Region 1, 27 are in Region 2, 2 are in Region 3, and 1 is in Region 4 (Cedar City District). Of the 50 intersections on each list, 43 are traffic signal-controlled. A total of 27,421 collisions occurred at the 50 intersections listed in Table 2.2 between 1994 and 2003, representing approximately 12 percent of all intersection crashes in Utah. A total of 7,132 collisions occurred at the 50 intersections listed in Table 2.3 between 2001 and 2003, or about 11 percent of all intersection crashes. A total of 33 intersections appear on both the 10-year and 3-year study period lists. One supposition of these intersections' recurrence is that no safety improvements were made to these locations between 1994 and 2003.

Intersections ranked based on crash severity scores are listed in Tables 2.4 (1994-2003) and 2.5 (2001-2003). The highest-scoring intersection on the 10-year list is 700 East (SR 71) and 3300 South (SR 171) in South Salt Lake, with 9,524.8 points. This intersection experienced five fatal crashes during the study period, the highest of all intersections in the state, and one of only two intersections to see more than three fatal crashes. The highest-scoring intersection on the 3-year list is 31st Street (SR 79) and Wall Avenue (SR 204) in Ogden, with 3,394.5 points. This intersection was one of just three in Utah to witness more than one fatal crash between 2001 and 2003. On the 10-year list, 16 of the intersections are in Region 1, 30 are in Region 2, and four are in Region 3. On the three-year list, 18 of the intersections are in Region 1, 19 are in Region 2, and 13 are in Region 3. The apparent jump in the number of intersections in Region 3 from 1994-2003 to 2001-2003 may be indicative of growth in Utah County. A total of 15 intersections "made" both the 10-year and 3-year lists. It is likely that there were no safety improvements at these locations during the study period. Four of the intersections on the 10-year list are not signal-controlled, while 13 of those on the 3-year list are not signalized. These intersections may be candidates for traffic signals, although several other factors would need to be considered as part of a signal warrant study. Non-signalized intersections are discussed in greater detail in Section 4.

Looking at all four intersection lists (Tables 2.2-2.5), all of the Region 1 locations are in Cache, Davis, or Weber County. All of the Region 2 locations are in Salt Lake County, and all of the Region 3 intersections are in Utah County. Only one intersection in Region 4 appeared on any of the lists, and it is located in St. George (St. George Boulevard and 1000 East). The statistics suggest that recurrent crash sites are predominantly an urban problem, as all of the intersections on the four top 50 lists are located within Utah's five urbanized areas (as designated by the U.S. Census). The following six intersections appear on all four statewide top 50 lists:

• Redwood Road + 5400 South (SR 68 + SR 173 - Taylorsville)
• 700 East + 3300 South (SR 71 + SR 171 - South Salt Lake)
• 12th Street + Washington Boulevard (SR 39 + US 89 - Ogden)
• 3500 South + 3600 West (SR 171 + 350600 - West Valley City)
• 3500 South + 5600 West (SR 171 + SR 172 - West Valley City)
• 5600 South + 1900 West (SR 97 + SR 126 - Roy)

Five of the intersections are in Region 2 (Salt Lake County) and two are in Region 1 (Weber County). These intersections are examined in greater detail in Section 5 of this report.

2.3 Fatal Crashes

There were 2,918 fatal crashes in Utah between 1994 and 2003, and 783 between 2001 and 2003. Not all of the crashes occurred at intersections. Some took place on freeways, while others were not intersection-related. Still others occurred off of the State Route system. The research team did not tabulate all of the intersections experiencing a fatal crash during the study period, but the following statistics were observed.

Between 1994 and 2003:

• One intersection (700 East and 3300 South in South Salt Lake) witnessed five fatal crashes.
• One intersection (8400 West and 2400 South in Magna) experienced four fatal crashes.
• Nine intersections witnessed three fatal crashes.
• Numerous intersections (probably over 100) experienced two fatal crashes.

Between 2001 and 2003:

• Three intersections (21st Street and Pennsylvania Avenue in Ogden, University Avenue and 200 North in Provo, and 2400 South and 8000 West in Magna) had two fatal crashes.
• Numerous intersections witnessed one fatal crash.

If statewide "top 50" lists of intersections experiencing fatal crashes were prepared for the 10- and 3-year study periods, then all intersections with two or more fatal crashes between 1994 and 2003, and all intersections having at least one fatal crash between 2001 and 2003 would be included (well over 50 on each list!). A total of 32 intersections would appear on both lists. These are shown in Table 2.6. One perspective on these intersections is that fatal crashes recur at these locations. This hypothesis cannot be proven statistically because the number of fatal crashes at any single location is very small. Nonetheless, this subset of 32 intersections may warrant further investigation. The following eleven intersections appear in Table 2.6 and on both the 10- and 3-year statewide lists (Tables 2.4 and 2.5 or Tables 4.2 and 4.3 for non-signalized intersections. These are discussed in Section 4):

• Hinckley Drive and Pennsylvania Avenue (SR 79 at milepoint 1.11 - Ogden)
• Main Street and Airport Drive (2500 North) (US 91 + 050370 - North Logan)
• State Street and Wood Avenue (1580 South) (US 89 at milepoint 323.58 - Salt Lake City)
• University Avenue and 3700 North (US 189 + 490740 - Provo)
• 700 East and 3300 South (SR 71 + SR 171 - South Salt Lake)
• 1900 West and 4400 South (SR 126 + 570090 - Roy)
• 2400 South and 8000 West (SR 111 at milepoint 7.71 - Magna CDP)
• 3500 South and Stanton Street (4640 West) (SR 171 at milepoint 4.73 - West Valley City)
• 3500 South and 4200 West (SR 171 at milepoint 5.28 - West Valley City)
• 5400 South and 4460 West (SR 173 at milepoint 4.07 - West Valley City)
• 5400 South and 5030 West (SR 173 at milepoint 3.35 - West Valley City)

As noted earlier, 700 East and 3300 South also appears on all four statewide lists (Tables 2.2-2.5), while University Avenue and 3700 North also appears on all four lists for Region 3 (Tables 3.8-3.11). All of the intersections listed above are discussed in greater detail in Section 5.

2.4 Intersection Crash Rates

The research team used the updated version of the CDDS to find high crash rates among intersections between Utah's state routes. The crash rates represented an added feature in the new version of the CDDS that was not available in the version used by the research team for the bulk of the study. Crash rates for "full" intersections (i.e., all approaches) were tabulated in the CDDS for state route intersections only (i.e., intersections between two state routes). Crash rates for intersections between state and non-state routes considered the traffic volume (and crashes) on the state route only. Intersections with crash rates greater than or equal to two per million entering vehicles, based on year 2001-2003 crashes and volumes, are listed in Table 2.7. The research team was unable to access crash rate data from Region 4, Cedar City District (specifically: SR 9 and SR 14).

The highest crash rate was 4.54 per million entering vehicles, at the intersection of state routes 101 and 165 (Main Street and 800 East) in Hyrum. This is a comparatively low-volume intersection, but the 30 crashes that occurred there between 2001 and 2003 were associated with a high crash rate. Thirteen of the 29 intersections are in Region 1, 13 are in Region 2, and 3 are in Region 3. Seven intersections had a crash rate of 3 or more per million entering vehicles, while one, mentioned above, had a crash rate greater than 4. To evaluate these intersections, it would be appropriate to compare the actual crash rate with the expected crash rate. It is interesting to note that the geographical distribution of the intersections in Table 2.7 (and Table 2.6) is less heavily "influenced" by Region 2 than the distributions in Tables 2.2-2.5. One interpretation is that fatal crashes and high crash rates are dependent on factors other than the high traffic volumes that one would expect in Region 2. Some additional considerations on these other factors are offered in Section 5.

Table 2.2  50 Utah Intersections with a Large Number of Crashes: 1994-2003

Table 2.3  50 Utah Intersections with a Large Number of Crashes: 2001-2003

Table 2.4  50 Utah Intersections with High Crash Severity Scores: 1994-2003

Table 2.5  50 Utah Intersections with High Crash Severity Scores: 2001-2003

Notes:

1. CDDS = Crash Data Delivery System. Data for intersections between two state highways were obtained from the "SR Intersections" tool. Data for intersections between a state highway and a federal-aid road were obtained from the "Intersections" tool. Crash totals by severity were obtained using the "Advanced Search" tool.
2. Each score was computed by assigning the following "weights" by crash severity: 1,000 - fatal; 100 - broken bones & bleeding wounds; 10 - bruises & abrasions; 1 - possible injury; 0.1 - no injury. The weights are based, approximately, on the societal cost of each crash outcome.
3. Two- and three-digit routes are state highways. Six-digit routes are federal-aid roads.
4. The number disagrees with that provided by the "SR Intersections" tool. The value shown was obtained from the "Advanced Search" tool. In most cases, the values obtained from the two tools were the same.

Other Notes:
Italicized locations are not signalized. Italicized scores correspond to locations at which crash data were available only for the state route (and not for the cross-street). NA = not applicable or not available. WVC = West Valley City.

Table 2.6  32 Utah Intersections with ≥ 2 Fetal Crashes 1994-2003 and ≥ 1 Fetal Crash 2001-2003

Notes: A bold number in the "Fatal" column means that the intersection had two fatal crashes between 2001 and 2003. All other intersections experienced one fatal crash between 2001 and 2003. Italicized locations are not signalized. Italicized scores indicate that crash data were not available for the cross-street. The intersections are not ranked.

Table 2.7  29 Utah State Route Intersections with Crash Rates ≥ 2: 2001-2003 Data

Note: Crash rate = total number of crashes per million entering vehicles (2001-2003). The total number of entering vehicles at each intersection is actually the year 2003 entering vehicles multiplied by 3. Italicized intersections are not signalized.