As a supplement to the crash-based (reactive) network screening analysis used to develop the High Injury Network (HIN), this Systemic Analysis uses a proactive approach to identify risk factors commonly associated with fatal and serious injury crashes and evaluates the road network based on site-specific risk levels. While the HIN targets locations with a high concentration of historical crashes, the systemic analysis focuses on locations with a significant risk of severe crashes, regardless of crash history. By focusing on where crashes are more likely to occur in the future, this proactive approach enables road owners to prioritize higher-risk locations for preventative safety improvements before a significant number of severe crashes occur.
The screening and prioritization process of systemic analysis, as described in the Systemic Safety User Guide by the Federal Highway Administration (FHWA), typically consists of six steps:
Identify focus crash types that represent the highest frequency of severe crashes or highest potential of a severe crash on the system.
Identify focus facility types where focus crashes most frequently occur.
Identify risk factors that are most correlated with an increased risk of a severe focus crash type on a focus facility type.
Identify system elements (i.e., roadway segments, intersections, curves) from the focus facility type that have features associated with each risk factor.
Calculate a risk score for each system element based on the presence and weight of applicable risk factors.
Prioritize system elements by ranking them from highest to lowest risk scores.
The results of systemic analysis can support the development of comprehensive safety plans and inform the installation of low-cost proven safety countermeasures to effectively reduce fatalities and serious injuries at scale.1
The Massachusetts Department of Transportation (MassDOT) first implemented the systemic approach for network screening with a grant received from the United States Department of Transportation (USDOT) in 2020 as part of the competitive Safety Data Initiative (SDI) process. Following FHWA’s systemic analysis process, MassDOT identified focus crash types, facility types, and risk factors for each emphasis area outlined in the 2018 Strategic Highway Safety Plan (SHSP). In 2023, the analysis was updated using crash data from 2017 to 2021. A Risk-Based Network Screening Tool was developed accordingly in the IMPACT portal, allowing users to visualize the systemic network screening results and filter top-ranked high-risk sites.
This memo draws on findings from the Risk-Based Network Screening Tool to summarize the systemic analysis results for each key emphasis area, as identified in the Existing Conditions Report, as shown below.
Intersections
Vulnerable Road Users (VRU)
Lane Departure
Older Drivers
Large Vehicles
Speeding
These summaries can support the MPO in strategically identifying and addressing locations with the greatest potential for future severe crashes across the region’s network.
The IMPACT Risk-Based Network Screening Tool is the primary data source for the systemic analysis result summaries. The tool provides outputs identifying high-risk towns, road segments, and intersections at the MPO level for most of the SHSP emphasis areas based on specific risk factors for each emphasis area. Each emphasis area targets specific focus facility types, so not all segments and intersections are included in the analysis.
In addition, roadway attribute data from MassDOT’s Road Inventory (2022) were used to analyze the distribution of roadway segments by risk level across different jurisdictions. Since the systemic analysis for large vehicle-involved crashes had not been updated by MassDOT using the most recent crash data and the speeding-related systemic analysis was completed only at the town level, fatal and serious injury crash data from 2018 to 2022 also were collected from the MassDOT Data Query and Visualization Tool. These crashes were combined with the road inventory data to determine focus facility types and risk factors and to identify high-risk sites for large vehicle-involved and speeding-related crashes.
This section of the report summarizes the key findings from the MassDOT IMPACT Risk-Based Network Screening Tool, as well as the additional analysis completed for emphasis areas not covered by the tool. For the risk-based network screening, MassDOT prioritized sites by ranking them based on risk scores derived from site-specific risk factors for each emphasis area. Sites ranked in the top 5th percentile were classified as “Primary Risk Sites,” indicating the highest risk for the emphasis area, while the next-highest 10th percentile were “Secondary Risk Sites,” representing a moderate risk. All remaining sites were considered “Not a Risk Site.”
The MassDOT IMPACT Risk-Based Network Screening Tool visualizes primary and secondary risk sites for each emphasis area at both the state and MPO levels. The tool provides the following outputs that correspond to the region’s key emphasis areas identified through the Existing Conditions report:
Intersections: Focus facility types for intersections, split into primary risk sites and secondary risk sites.
Vulnerable Road Users: Focus facility types for both segments and intersections for pedestrians and bicyclists separately, split into primary risk sites and secondary risk sites. For this analysis, the pedestrian and bicyclist risk sites were combined into one VRU layer.
Lane Departure: Focus facility types for segments, split into primary risk sites and secondary risk sites.
Older Drivers: Focus towns, split into primary risk towns and secondary risk towns. This analysis was not done at the segment or intersection level as older driver crashes are not as easily tied to specific roadway attributes. Older driver interventions are primarily more behavior based rather than infrastructure based.
Speeding: Focus towns, split into primary risk towns and secondary risk towns. However, this report goes deeper and manually analyzes speeding at the segment level.
Large Vehicle: There are no current outputs from the tool, so a manual systemic analysis was completed for this emphasis area as well.
Key takeaways from the systemic analysis performed for the Boston Region MPO include:
Key Takeaways
Traffic volumes, the number of approach lanes, and the type of intersection control are all key risk factors at intersections.
Of the 314 centerline miles identified as primary risk sites for vulnerable road user-involved crashes, 78 percent are under municipal jurisdiction.
The majority of lane departure crashes occur on two-lane, two-way undivided highways. These roads are the highest-risk sites for lane departure fatalities and serious injuries.
Towns north of the inner core of the region, such as Revere, Saugus, Lynn, and Peabody, are most at-risk for older driver crashes.
Roads under MassDOT jurisdiction have the highest proportion of mileage considered as high-risk for large vehicle-involved crashes.
Narrow medians, wide traveled ways, and low traffic volumes are key risk factors of speeding-related crashes on urban uncontrolled roads.
Due to space constraints, for emphasis areas with multiple focus facility types, the associated risk factors were combined by category in the table. The full list of risk factors for each focus facility type within each emphasis area is provided in Appendix A, along with a summary of sites by jurisdiction and risk category. For the “Large Vehicle” and “Speeding” emphasis areas, the full systemic analysis methodology also is included in Appendix A.
Table 2.1 | Facility Types and Risk Factors Identified for Each Key Emphasis Area
Emphasis Area
Focus Facility Type
Risk Factor Category
Intersection Angle Crashes
All intersections (except roundabouts, other circular intersections, and non-conventional intersections)
Intersection major approach annual average daily traffic (AADT)
Intersection minor approach AADT
Respective town meets three Environmental Justice criteria1
Number of through lanes on major road
Intersection traffic control type
Number of intersection approaches
VRU Crashes—Segments
Principal Arterials
Minor Arterials
Major Collectors
Segment length
Segment AADT
Roadway attributes, including shoulder type, median type, curb presence, sidewalk width, number of lanes, etc.
Posted speed limit
Segment proximity to destinations, including liquor stores, bike trails, transit, colleges, etc.
Segment proximity to hazardous waste
Biking and walking potential2
Environmental Justice criteria
Block group socio-economic characteristics, including population density, median household income, employee density, etc.
Segment proximity to different land use types, including Commercial, Mixed use residential, etc.
Percentage of commuters walking, biking, and using transit
VRU Crashes—Intersections
All intersections (except roundabouts, other circular intersections, and non-conventional intersections)
Intersection major approach AADT
Intersection minor approach AADT
Presence of lighting
Respective town meets three environmental justice criteria
Number of intersection approaches
Number of through lanes on major road
Urban type
Biking and walking potential2
Intersection traffic control type
Land use mix
Intersection proximity to destinations, including liquor stores and transit stops
Lane Departure Crashes
Urban two-lane, two-way undivided highways
Rural two-lane, two-way undivided highways
Segment length
Segment AADT
Federal functional classification
Roadway attributes, including shoulder type and width, curb presence, surface width, etc.
Posted speed limit
Number of Alcoholic Beverage Control Commission (ABCC) Licenses within a quarter mile of the segment
Presence of horizontal curvatures
Terrain type
Older Driver-Involved Crashes
Analysis was performed at town level
Proportion of mileage that is Interstate, freeway, or expressway
Number of senior care providers and assisted living facilities in town
Number of traffic citations, including impaired driving citations and speeding citations per centerline mile in the town
Town-level demographic characteristics, including population aged over 64, percentage of population aged over 64 with self-reported cognitive issues, and proportion of licensed drivers aged over 64
Large Vehicle-Involved Crashes
Urban uncontrolled principal arterials (other)
Urban uncontrolled minor arterials
Segment AADT
Roadway attributes, including shoulder type, surface width, median width, etc.
Posted speed limit
Roadway jurisdiction
Speeding-Related Crashes
Urban uncontrolled principal arterials (other)
Urban uncontrolled minor arterials
Urban uncontrolled major collectors
Urban uncontrolled local roads
Segment AADT
Roadway attributes, including shoulder width, median width, surface width, curb presence, etc.
Posted speed limit
1 Environmental Justice criteria, determined by Massachusetts Executive Office of Energy and Environmental Affairs (EEA), include: 1. Income: the annual median household income is 65 percent or less of the statewide annual median household income; 2. Minority: minorities make up 40 percent or more of the population; 3. English Isolation: 25 percent or more of households identify as speaking English less than "very well"; 4. Minorities make up 25 percent or more of the population and the annual median household income of the municipality in which the neighborhood is located does not exceed 150 percent of the statewide annual median household income.
To better view the systemic network, an online application was created as seen in Figure 2.1. In addition to the ability to view the systemic network, this online application allows for comparison between the Systemic Network and the HIN to see where there are overlaps and similarities. Each network was developed through a different methodology so it is not expected that they identify identical locations. Locations that are identified as being on both the Systemic Network and HIN should be reviewed independently to determine if all fatal and serious injury crashes are tied to systemic issues or if there is a need for supplemental tailored treatments.
The HIN and systemic network will lead to reactive and proactive project types at the regional level, as well as provide information to the subregions and municipalities on where potential improvements should be considered. The HIN, systemic analysis, and existing conditions analysis will support decision making by key stakeholders and the Task Force to lead safety project prioritization in the Boston Region. The combination of these three pieces will inform the strategies and actions within the implementation action plan.
Outside of the formal data analysis, a key next step in the Vision Zero Action Plan will be the development of subregion safety profiles that describe the common infrastructure, behavioral, operational, and modal safety problems in each subregion. These profiles will combine results from the Existing Conditions Report, the HIN, outreach activities, and more aspects of the plan to provide a holistic view of safety specific to each subregion.
This appendix outlines the development of focus facility types and associated risk factors for the region’s key emphasis areas. A complete list of focus facility types and risk factors identified for each emphasis area is provided. This appendix also discusses the methodology used for the manual systemic analysis of large vehicle crashes and speeding-related crashes.
The systemic analysis of intersection crashes was performed by MassDOT and focused on multi-vehicle angle crashes, defined as those where the first harmful event was a “collision with a motor vehicle in traffic” and the manner of collision was “angle.” All angle crashes that occurred at four-way intersections, T-intersections, Y-intersections, traffic circles, or intersections with five or more legs were considered.
To determine the focus facility types where fatal and serious injury intersection angle crashes most commonly occur, MassDOT developed a crash tree to analyze crash distribution by intersection geometry and traffic control type. All intersections except circular intersections and non-conventional intersections were included as focus facility types. For these selected intersections, risk factors that potentially contribute to an increased risk of severe intersection angle crashes were assessed using various datasets, including intersection inventory data, land use data, and environmental justice data. Eight risk factors were identified:
Major approach Annual Average Daily Traffic (AADT)
Minor approach AADT 1,500 and above
Respective town meets three Environmental Justice criteria2
Three or more through lanes on major approach
Two-way stop-control
All-way stop-control
Signalized control
Four or more intersection legs
MassDOT assigned an equal weight to each risk factor, except for “All-way stop-control,” which was given a weight of 0.75, and “Major Approach AADT,” which received a variable weight ranging from 0 to 1 based on the major approach AADT value. A normalized risk score was then calculated for each intersection, and a percentile rank was generated at the MPO level. Further details on the risk factor identification and facility scoring process can be found in the Risk Factors for SHSP Emphasis Areas report published by MassDOT. An example application of the scoring process also is provided in Appendix B using a randomly selected intersection in the region to illustrate how MassDOT evaluated site-specific risk levels after identifying focus facility types and risk factors.
Within the region, intersections ranked in the top 5 percent were categorized as “Primary Risk Intersection,” and intersections ranked in the next 10 percent were categorized as “Secondary Risk Intersection.” Figure A.1 summarizes the number of intersections by risk category and jurisdiction.
Table A.1 | Intersections by Risk Category and Jurisdiction (Intersection Angle Crashes)
Note: Data provided by the tool only specify intersection jurisdiction as MassDOT or non-MassDOT; The table includes all intersections (except roundabouts, other circular intersections, and non-conventional intersections).
Since VRUs are susceptible to serious injuries and fatalities in crashes involving motor vehicles, a systemic analysis was performed by MassDOT for pedestrian crashes and bicyclist crashes at both segment and intersection levels.
For pedestrian and bicyclist fatal and serious injury crashes on roadway segments, the crash distribution by functional classification identified principal arterials, minor arterials, and major collectors as focus facility types. Separate sets of segment-level risk factors were identified for each focus facility type, using a combined dataset of roadway attributes, biking-walking infrastructure, land use types, and socioeconomic considerations at the block group level. Full lists of the identified risk factors for each focus facility type are provided in Table A.2 through Table A.4.
Table A.2 | Segment-level Risk Factors for VRU-Involved Crashes on Principal Arterials (Other)
Focus Facility Type
Risk Factor (Pedestrian)
Risk Factor (Bicycle)
Principal Arterials
Natural Log of segment length
AADT over 8,000
Curbs on both sides
3 or more total lanes on the segment
“Medium” or “High” Walking potential
Bike trails present within a half mile
Colleges present within a half mile
Transit stops present within a quarter mile
Segment within 100 feet of area zoned as “Commercial”
Segment within 100 feet of area zoned as “Mixed Use Commercial”
Segment within 100 feet of area zoned as “Mixed Use Residential”
Segment within 100 feet of area zoned as “Residential Multifamily”
Total population of the respective block group over 3,000
Respective block group meets at least one Environmental Justice criterion1
Percentile of low life expectancy in the respective census tract
Natural Log of segment length
AADT over 9,000
Curbs on both sides
No shoulder present
No median present
Two-way traffic operation
Posted Speed Limit over 30 miles per hour (mph)
“High” Biking Potential
Bike trails present within a half mile
Alcohol sold within a quarter mile
Respective census tract classified as 'Environmentally Disadvantaged' by USDOT
Population density of the respective block group over 8,000 per square mile
Hazardous waste present within a quarter mile
Segment within 100 feet of area zoned as “Commercial”
Segment within 100 feet of area zoned as “Mixed Use Other”
Segment within 100 feet of area zoned as “Open Land”
Percentage of the population aged over 64 in the respective block group
1 Environmental Justice criteria, determined by Massachusetts Executive Office of Energy and Environmental Affairs (EEA), include: 1. Income: the annual median household income is 65 percent or less of the statewide annual median household income; 2. Minority: minorities make up 40 percent or more of the population; 3. English Isolation: 25 percent or more of households identify as speaking English less than “very well;” 4. Minorities make up 25 percent or more of the population and the annual median household income of the municipality in which the neighborhood is located does not exceed 150 percent of the statewide annual median household income.
Considering the quality of available data and the potential impact of each risk factor on pedestrian and bicyclist crashes, a weighted sum of the identified risk factors was calculated for each segment within its respective focus facility type and normalized at the MPO level. A corresponding percentile rank was then computed. Similar to the analysis performed for intersection multi-vehicle angle crashes, segments were categorized into three risk levels based on their percentile ranks. The systemic analysis process for the pedestrian crashes and bicyclist crashes is documented in detail in the Risk Factors for SHSP Emphasis Areas: Pedestrian Crashes and Risk Factors for SHSP Emphasis Areas: Bicycle Crashes reports.
To determine the overall segment risk categories for VRU crashes, segment risk levels derived from pedestrian and bicyclist systemic analyses were combined by selecting the higher of the two. Within the region, 10 percent of selected focus facilities (measured by centerline miles) were identified as primary risk sites, with 78 percent of those miles (246 out of 314 miles) under municipal jurisdiction. Table A.5 summarizes the number of VRU crash sites by risk category and jurisdiction.
Table A.5 | Centerline Miles by Risk Category and Jurisdiction (VRU Crashes)
Jurisdiction
Primary Risk Site
Secondary Risk Site
Not a Risk Site
Total
Number
Percentage
Number
Percentage
Number
Percentage
Municipality
245.6
10%
371.5
15%
1,827.2
75%
2,444.3
MassDOT
54.3
8%
64.4
9%
575.9
83%
694.6
DCR
14.1
11%
36.0
27%
84.1
63%
134.2
Other1
0.0
0%
1.9
33%
3.8
67%
5.7
Total
314.3
10%
473.8
14%
2,491.0
76%
3,278.8
1 Jurisdiction category “Other” includes Massachusetts Port Authority, State Park or Forest, State Institutional, Federal Park or Forest, County Institutional, U.S. Air Force, U.S. Army Corps of Engineers, Federal Institutional, Private, U.S. Army.
Note: This table only includes the identified focus facility types (principal arterials, minor arterials, and major collectors).
For intersection-related pedestrian and bicyclist crashes, all intersections (except roundabouts, other circular intersections, and non-conventional intersections) were considered as focus facility types. Risk factors were identified based on intersection-level attributes and community-based characteristics, with a complete list provided in Table A.6.
Table A.6 | Intersection-level Risk Factors for VRU-Involved Crashes
Focus Facility Type
Risk Factor (Pedestrian)
Risk Factor (Bicycle)
All intersections (except roundabouts, other circular intersections, and non-conventional intersections)
Major approach AADT between 3,000 and 5,999
Major approach AADT between 6,000 and 11,999
Major approach AADT 12,000 and above
Minor approach AADT 1,000 and above
Three or more through lanes on major approach
Respective town meets three Environmental Justice criteria1
Alcohol sold within a quarter mile
Transit stops present within a quarter mile
Four-leg intersection
Signalized control
Intersection located in urban areas
Proportion of impervious land
Land use mix
Proportion of institutional land use
Major approach AADT between 5,000 and 9,999
Major approach AADT between 10,000 and 14,999
Major approach AADT above 15,000
Minor approach AADT above 1,500
Three or more lanes on minor approach
Lighting present
Respective town meets three Environmental Justice criteria
Transit stops present within a quarter mile
Number of liquor stores within a quarter mile
Four-leg intersection
Signalized control
Yield control
Biking Potential
Intersection located in urban areas
Land use mix
1 Environmental Justice criteria, determined by Massachusetts Executive Office of Energy and Environmental Affairs (EEA), include: 1. Income: the annual median household income is 65 percent or less of the statewide annual median household income; 2. Minority: minorities make up 40 percent or more of the population; 3. English Isolation: 25 percent or more of households identify as speaking English less than “very well;” 4. Minorities make up 25 percent or more of the population and the annual median household income of the municipality in which the neighborhood is located does not exceed 150 percent of the statewide annual median household income.
Based on the weighted sum of these risk factors for each intersection and the corresponding percentile ranks within the Boston Region MPO, Table A.7 shows that 7 percent of intersections were classified as “Primary Risk Sites”. Notably, intersections under MassDOT jurisdiction have a higher proportion of primary and secondary risk sites (31 percent) compared to those under non-MassDOT jurisdiction (18 percent).
Table A.7 | Intersections by Risk Category and Jurisdiction (VRU Crashes)
Note: Data provided by the tool only specify intersection jurisdiction as MassDOT or non-MassDOT;
The table includes all intersections (except roundabouts, other circular intersections, and non-conventional intersections).
For a more complete understanding of pedestrian and cyclist safety issues and which areas to focus VRU safety improvements, the high-risk locations identified through systemic analysis can be layered with historically high-crash frequency locations from the MassDOT Crash-based Network Screening Analysis, as discussed in the 2023 Massachusetts Vulnerable Road User Safety Assessment. Using this combined approach, MassDOT identified the top 5 percent of towns considered high risk based on each town’s pedestrian and bicyclist crash history and coverage of top-risk sites. Notably, 13 of the 17 identified high-risk towns fall within the Boston Region, including:
Cambridge
Boston
Somerville
Brookline
Waltham
Chelsea
Lynn
Everett
Medford
Quincy
Malden
Revere
Newton
As one of the five MPOs that cover the identified high-risk towns, the Boston Region MPO should prioritize those within the region for targeted systemic safety improvements to proactively reduce the risk of future severe crashes.
Lane departure crashes have been a leading cause of fatal and serious injury crashes both statewide and within the region. The systemic analysis performed by MassDOT for lane departure crashes included all crashes in which the first harmful event involved a collision with a fixed object, running off the road, or crossing the centerline/median.
MassDOT identified urban and rural two-lane, two-way undivided highways as focus facility types for lane departure crashes. Due to limited AADT data for many local roads, these two facility types were further divided into four categories based on the availability of AADT information. Separate sets of risk factors were then identified for each facility category using roadway attribute data and operational data at the segment level, along with town-level data on Alcoholic Beverage Control Commission (ABCC) licenses. Table A.8 and Table A.9 present the complete sets of risk factors for urban and rural two-lane undivided roadway segments.
Table A.8 | Risk Factors for Lane Departure Crashes on Urban, Two-Lane, Undivided Roads
Focus Facility Type
Risk Factor
(Roads with Known AADT)
Risk Factor
(Roads with Unknown AADT)
Urban, Two-Lane, Undivided Roads
Natural Log of AADT
Federal functional class is principal arterial (other) or minor arterial
Federal functional class is major collector or minor collector
Average shoulder width 4 feet or less
Surface width 23 feet or more
1 or fewer ABCC Licenses within a quarter mile of the segment
MPO is Middlesex or Pioneer
MPO is Old Colony or Southeast
MPO is Cape Cod or Montachusett
Horizontal curvature present ranging from 3.5 degrees to 13.9 degrees
No curb present
Curb present on one side of roadway
At least one ABCC license within a quarter mile of the segment
Surface width 22 feet or less
MPO is not Cape Cod
MPO is Southeast
Horizontal curvature present ranging from 3.5 degrees to 13.9 degrees
Based on the identified risk factors, normalized risk scores and percentile ranks were calculated for each segment within the region. Table A.10 summarizes the distribution of roadway segments by risk site category and jurisdiction.
Table A.10 | Centerline Miles by Risk Category and Jurisdiction (Lane Departure Crashes)
Jurisdiction
Primary Risk Site
Secondary Risk Site
Not a Risk Site
Total
Number
Percentage
Number
Percentage
Number
Percentage
Municipality
492.7
6%
922.5
12%
6,469.4
82%
7,884.7
MassDOT
36.6
14%
77.5
30%
142.9
56%
257.0
DCR
13.6
21%
16.7
25%
35.3
54%
65.6
Other1
1.1
0%
38.4
6%
558.6
93%
598.1
Total
544.0
6%
1,055.1
12%
7,206.3
82%
8,805.4
1 Jurisdiction category “Other” includes Massachusetts Port Authority, State Park or Forest, State Institutional, Federal Park or Forest, County Institutional, U.S. Air Force, U.S. Army Corps of Engineers, Federal Institutional, Private, U.S. Army.
Note: This table only includes the identified focus facility types (urban two-lane, two-way undivided highways and rural two-lane, two-way undivided highways).
Due to the prevalence of older driver-involved fatal and serious injury crashes among various facility types, MassDOT performed the systemic analysis at the town-level to prioritize
communities for education campaigns and safety initiatives focused on older road users. The analysis identified eight town-level risk factors applicable to the region, including:
Proportion of mileage that is Interstate, freeway, or expressway
Absence of senior care providers in town
More than 0.5 annual impaired driving citations per centerline mile in the town
More than 3 annual speeding citations per mile in the town
Natural log of persons aged 65 or older in the town
Less than 3 assisted living facilities in the town
Percentage of persons aged 65 or older with self-reported cognitive issues
Proportion of licensed drivers aged 65 or older
MassDOT assigned a risk score between 0 and 1 to each risk factor, and ranked towns at the MPO level using the normalized combined risk scores and percentile ranks.
In the Boston Region MPO, the systemic analysis identified five primary risk towns, representing 10 percent of the region’s population and 6 percent of its roadway mileage. Additionally, 10 secondary risk towns were identified, accounting for an additional 12 percent of the population and 11 percent of roadway mileage. Detailed information on these towns is provided in Table A.11 (Primary Risk Towns) and Table A.12 (Secondary Risk Towns), with towns listed in descending order based on their percentile ranks within the region.
1 As identified in the Existing Conditions Report, the City of Waltham likely has inaccurately coded fatal and serious injury crash data. Despite this leading to potentially misleading analysis, Waltham was kept in this table to ensure consistency with the results of MassDOT’s approach to older driver systemic screening.
Note: This table includes Interstates and other fully access-controlled roadways.
The five primary risk towns in Table A.11 were identified mainly due to a combination of a greater older population (more than 5,600) and a significant proportion (over 6 percent) of older adults with self-reported cognitive issues. To address the elevated crash risk in these areas, potential countermeasures, including improved roadway signage and overall visibility, and targeted education programs on safe driving practices for older adults, should be considered.
In the MassDOT risk-based network screening, large vehicle-involved crashes are defined as crashes involving a single-unit or larger truck or a bus. While relatively infrequent, crashes involving large vehicles tend to result in more severe outcomes compared to those involving passenger vehicles, and were therefore identified as a focus crash type in the systemic analysis performed by MassDOT in 2017. However, this analysis has not been updated to incorporate more recent crash data, and its results have not been integrated into the IMPACT Risk-Based Network Screening Tool. Given that large vehicle-involved crashes are still considered an emphasis area for the Boston Region MPO, the previous systemic analysis was updated using a similar approach based on crash data from 2018 to 2022.
Between 2018 and 2022, 312 of 4,770 (6.5 percent) fatal and serious injury crashes in the region involved large vehicles. Since most of these large vehicle-involved crashes occurred on roadway segments (60 percent), the analysis focused on segment-level crashes to identify focus facility types, and a crash tree was developed accordingly.
Figure A.1 shows the distribution of large vehicle-involved fatal and serious injury crashes on segments by access control type and functional classification. Although segments with full access control, such as Interstates and other expressways or freeways, account for a significant share of large vehicle crashes (39 percent), they will not be included as potential focus facility types, as this analysis focuses on local roads to more effectively address the areas where interventions are most needed and can have the greatest impact on reducing fatal and serious injury crashes.
After the exclusion of Interstates and other expressways and freeways, urban uncontrolled principal arterials (other) and urban uncontrolled minor arterials were identified as focus facility types, as they accounted for the highest proportion of large vehicle-involved crashes among the remaining facility types (underscoredin Figure A.1).
Figure A.1 | Crash Tree for Large Vehicle-Involved Segment Crashes
Source: MassDOT IMPACT Crash Tree Builder.
Note: This chart includes fatal and serious injury crashes along Interstates and other fully access-controlled roadways.
Following the selection of focus facility types, the overrepresentation approach was used to determine potential risk factors. Using 2018 to 2022 crash data obtained from the MassDOT IMPACT tool and 2022 road inventory data, factors related to crash characteristics, roadway attributes, and involved vehicles and persons recorded in the crash dataset were examined.
For each focus segment type, an attribute was considered a risk factor if the proportion of large vehicle-involved fatal and serious injury crashes with that attribute was statistically higher than the proportion of centerline miles with the same attribute within that facility type. Statistical significance was determined by constructing 90 percent confidence intervals around the proportion.
For urban uncontrolled principal arterials, no statistically significant risk factor was identified relevant to large vehicle-involved crashes. However, a slight overrepresentation of crashes was observed on segments with the following characteristics: AADT above 20,000, left side curb only, MassDOT jurisdiction, four travel lanes, right shoulder width between 4 and 12 ft, right sidewalk width between 9 and 12 ft, speed limits of 40 mph or above, and traveled way width less than 25 ft. While these factors did not reach statistical significance in this analysis, the observed overrepresentation suggests that there are potential correlations with large vehicle-involved crashes. Thus, these factors should still be considered in future screening efforts.
For urban uncontrolled minor arterials, Table A.13 presents the risk factors identified for large vehicle-involved crashes, along with the percentages of crashes and roadway mileages to help prioritize higher-risk facility elements for safety improvements.
Table A.13 | Risk Factors for Large Vehicle Crashes on Urban Uncontrolled Minor Arterials
Risk Factor
Risk Factor Criteria
Large Vehicle Fatal and Serious Injury Crashes
Urban Uncontrolled Minor Arterials
Crash
Number
Crash Percentage
Centerline Miles
Mileage Percentage
AADT
20,000–30,000
5
17%
43.2
3%
Curb
Right side only
6
20%
91.8
7%
Jurisdiction
MassDOT
7
23%
119.6
9%
Road Surface Width
> 30 ft
15
50%
437.7
34%
Right Shoulder Type
No Shoulder
23
77%
750.5
58%
Right Sidewalk Width
4–9 ft
17
57%
481.6
37%
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes fatal and serious injury crashes along Urban Uncontrolled Minor Arterials.
Road segments that have the characteristics noted above are considered to be at higher-risk for large vehicle-involved crashes. Roads that meet multiple risk factors would be considered to be most at-risk for large vehicle-involved crashes.
For each focus segment type, risk factors were combined and weighted equally. A risk score was calculated for each segment based on the total number of applicable risk factors present. This risk score was then normalized by the maximum possible risk score for that facility type to allow for consistent prioritization across different facility types. Using the normalized risk scores, percentile ranks also were computed for each segment at the MPO level. Segments ranked in the top 5 percent were identified as a “Primary Risk Site,” and those in the next 10 percent were identified as a “Secondary Risk Site.”
Table A.14 summarizes the centerline miles of urban uncontrolled minor arterials by risk site category and jurisdiction for large vehicle crashes. Although only 120 miles of the facility type within the region are managed by MassDOT, these roads have the highest proportion (24 percent) of mileage considered as high risk for large vehicle-involved fatal and serious injury crashes, compared to 8 percent for DCR-owned roads and 14 percent for municipally owned roads. Location and risk assessment information of each individual segment within the identified focus facility types is available through an online application.
Table A.14 | Centerline Miles by Risk Site Categories and Jurisdictions (Large Vehicle Crashes)
Jurisdiction
Centerline Miles by Large Vehicle Crash Risk Site Categories (miles/percentages)
Primary Risk Site
Secondary Risk Site
Not a Risk Site
Total
Municipality
45.8
4%
115.2
10%
960.0
86%
1,121.0
MassDOT
17.6
15%
10.9
9%
91.1
76%
119.6
DCR
1.3
2%
3.4
6%
50.4
92%
55.0
Other1
0.2
4%
0.7
13%
4.5
83%
5.5
Total
64.9
5%
130.2
10%
1,106.0
85%
1,301.1
1 Jurisdiction category “Other” includes Massachusetts Port Authority, State Park or Forest, State Institutional, Federal Park or Forest, County Institutional, U.S. Air Force, U.S. Army Corps of Engineers, Federal Institutional, Private, U.S. Army.
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes the identified focus facility types (urban uncontrolled minor arterials).
Given the substantial increase in speeding-related fatal and serious injury crashes across both the Commonwealth and the Boston Region over the past five years, addressing speeding-related issues remains a critical priority. While MassDOT updated its systemic analysis for speeding crashes with recent crash data, the analysis was limited to the town-level due to the lack of reliable operational speed data at individual sites.
Recognizing that even in the absence of operational speed data, the site-level systemic analysis still offers the advantage of identifying location-specific risk factors and enabling a more efficient prioritization of safety improvements based on detailed risk assessment, a separate site-level systemic analysis was performed for speeding crashes within the Boston Region. Crash data from 2018 to 2022 were obtained from the MassDOT IMPACT tool; and consistent with MassDOT’s definition, any crash in which the “Driver Contributing Circumstances” field indicated “Exceeded authorized speed limit” was considered as a speeding-related crash.
Within the region, a total of 270 speeding-related fatal and serious injury crashes occurred between 2018 and 2022. Similar to the pattern observed in large vehicle-involved crashes, 66 percent of speeding-related crashes occurred on roadway segments versus intersections. Given this high concentration of crashes on urban segments, a crash tree was developed accordingly to help identify the focus facility types for speeding-related crashes at the segment level.
As indicated in Figure 2.1, roadways with no access control accounted for the highest share of speeding-related fatal and serious injury crashes (67 percent), followed by roadways with full access control (25 percent). To prioritize segments where municipal-level safety interventions can be most effective, Interstates and other expressways or freeways were excluded from the analysis. Based on crash frequency, urban uncontrolled principal arterials (other), minor arterials, major collectors, and local roads were identified as focus facility types, each representing a significant portion of speeding-related fatal and serious injury crashes.
Figure A.2 | Crash Tree for Speeding-Related Segment Crashes
Source: MassDOT IMPACT Crash Tree Builder.
Note: This chart includes fatal and serious injury crashes along Interstates and other fully access-controlled roadways.
To identify risk factors associated with a higher risk of severe speeding-related crashes on the selected focus facilities, factors related to crash circumstances, roadway attributes, and details of involved vehicles and persons were analyzed separately for each facility type using the overrepresentation method described in the Large Vehicle-Involved Crashes section. Table A.15 through Table A.18 summarize the identified risk factors for speeding-related crashes on urban uncontrolled principal arterials (other), minor arterials, major collectors, and local roads.
Results suggest that speeding-related crashes were significantly more prevalent on segments with narrow medians (less than 5 feet wide) and wide traveled ways (more than 30 feet wide). Since wider travel lanes can create a false sense of safety at higher speeds, and narrow medians often provide insufficient separation between opposing traffic, this combination can increase both the chance of speeding and the severity of resulting crashes. Additionally, for urban uncontrolled principal arterials and minor arterials, low traffic volumes (below 5,000 AADT) also were found to be associated with an elevated risk of speeding-related crashes, even though such low volumes occur on only a small portion of these roadways. This may be due to a lack of congestion allowing drivers to travel at higher speeds with fewer interruptions.
Table A.15 | Risk Factors for Speeding Crashes on Urban Uncontrolled Principal Arterials (Other)
Risk Factor
Risk Factor Criteria
Speeding-Related Fatal and Serious Injury Crashes
Urban Uncontrolled Principal Arterials (Other)
Crash
Number
Crash Percentage
Centerline Miles
Mileage Percentage
AADT
0–5,000
116
89%
10.2
1%
Median Width
1–5 ft or > 100 ft
29
22%
52.9
8%
Road Surface Width
> 30 ft
44
34%
175.5
25%
Number of Opposing Lanes
2
23
18%
81.0
11%
Speed Limit
30–35 mph
87
67%
410.8
58%
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes fatal and serious injury crashes along Urban Uncontrolled Principal Arterials (Other).
Table A.16 | Risk Factors for Speeding Crashes on Urban Uncontrolled Minor Arterials
Risk Factor
Risk Factor Criteria
Speeding-Related Fatal and Serious Injury Crashes
Urban Uncontrolled Minor Arterials
Crash
Number
Crash Percentage
Centerline Miles
Mileage Percentage
AADT
0–5,000 or
> 30,000
150
94%
158.4
12%
Curb
Right side only
20
13%
91.8
7%
Median Width
1–5 ft
6
4%
13.9
1%
Right Shoulder Width
4–9 ft
11
7%
33.4
3%
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes fatal and serious injury crashes along Urban Uncontrolled Minor Arterials.
Table A.17 | Risk Factors for Speeding Crashes on Urban Uncontrolled Major Collectors
Risk Factor
Risk Factor Criteria
Speeding-Related Fatal and Serious Injury Crashes
Urban Uncontrolled Major Collectors
Crash
Number
Crash Percentage
Centerline Miles
Mileage Percentage
AADT
> 30,000
21
19%
2.8
0.2%
Curb
Left side only
12
11%
56.6
5%
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes fatal and serious injury crashes along Urban Uncontrolled Major Collectors.
Table A.18 | Risk Factors for Speeding Crashes on Urban Uncontrolled Local Roads
Risk Factor
Risk Factor Criteria
Speeding-Related Fatal and Serious Injury Crashes
Urban Uncontrolled Local Roads
Crash
Number
Crash Percentage
Centerline Miles
Mileage Percentage
Road Surface Width
> 30 ft
23
18%
750.3
10%
Terrain
Level terrain
106
83%
5,736.4
78%
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes fatal and serious injury crashes along Urban Uncontrolled Local Roads.
Using the selected risk factors, each segment within the identified focus facility types was assigned a normalized risk score, and a corresponding percentile rank at the regional level. Based on these rankings, segments were categorized as primary risk sites, secondary risk sites, or sites with no identified risk.
Table A.19 provides a detailed distribution of centerline miles by risk site categories across jurisdictions. Among all focus facilities, roadways under the local jurisdiction had the highest proportion of segments classified as “Primary Risk Sites” (5 percent) compared to other jurisdictions. Location and risk assessment information of each individual segment within the identified focus facility types is available through an online application.
Table A.19 | Centerline Miles by Risk Site Categories and Jurisdictions (Speeding Crashes)
Jurisdiction
Centerline Miles by Speeding Crash Risk Site Categories (miles/percentages)
Primary Risk Site
Secondary Risk Site
Not a Risk Site
Total
Municipality
484.7
5%
930.9
10%
7,765.8
85%
9,181.4
MassDOT
1.7
0.5%
14.7
4%
346.5
95%
362.9
DCR
1.8
2%
6.9
6%
103.9
92%
112.5
Other1
41.9
4%
107.8
11%
796.3
84%
946.0
Total
530.1
5%
1,060.1
10%
9,012.6
85%
10,602.9
1 Jurisdiction category “Other” includes Massachusetts Port Authority, State Park or Forest, State Institutional, Federal Park or Forest, County Institutional, U.S. Air Force, U.S. Army Corps of Engineers, Federal Institutional, Private, U.S. Army.
Source: MassDOT IMPACT Data Query and Visualization Tool and MassDOT Road Inventory 2022.
Note: This table only includes the identified focus facility types (urban uncontrolled principal arterials, minor arterials, major collectors, and local roads).
This appendix provides an example of the scoring process on a randomly selected intersection in the region to explain the scoring methodology used by MassDOT for the “Intersections” emphasis area. The example site is a two-way stop-controlled cross-intersection located at Everett Avenue (major approach) and Arlington Street (minor approach) in the Town of Chelsea.
For the “Intersections” emphasis area, all intersections (except roundabouts, other circular intersections, and non-conventional intersections) were considered focus facilities. The associated risk factors and their assigned weights are listed in Table B.1. A risk score is calculated for each risk factor based on whether the intersection meets the risk factor criteria and the according weight.
For the selected intersection, the relevant attributes corresponding to each risk factors are detailed in Table B.1, along with the calculated individual risk scores. By summing these individual risk scores, a total risk score of 4.9 is computed for the intersection site. To allow for comparison across different types of focus facilities, the total risk score is further normalized by the maximum possible risk score a site can achieve within each focus facility type. For this emphasis area, the maximum possible total risk score is 6. Thus, the normalized risk score for the selected intersection site is 0.82.
Table B.1 | Calculation Example of Normalized Risk Score
Risk Factor
Weight
Intersection Attribute
Risk Score
Major Approach AADT
Variable from 0 to 1 based on the range of major approach AADT
20,326
0.9
Minor approach AADT 1,500 and above
1
3,437
1
Respective town meets three environmental justice criteria
1
Respective town meets the “Minority”, “Income”, and “English Isolation” criteria
1
Three or more through lanes on major approach
1
Maximum number of through lanes on major approach is 2
0
Two-way stop-control
1
Two-way stop-control
1
All-way stop-control
0.75
Not all-way stop-control
0
Signalized control
1
Not signalized-control
0
Four or more intersection legs
1
Four intersection legs
1
Total Risk Score
4.9
Normalized Risk Score = Total Risk Score / Maximum Possible Risk Score
2 Environmental Justice criteria, determined by Massachusetts Executive Office of Energy and Environmental Affairs (EEA), include: 1. Income: the annual median household income is 65 percent or less of the statewide annual median household income; 2. Minority: minorities make up 40 percent or more of the population; 3. English Isolation: 25 percent or more of households identify as speaking English less than "very well"; 4. Minorities make up 25 percent or more of the population and the annual median household income of the municipality in which the neighborhood is located does not exceed 150 percent of the statewide annual median household income.
