HSM Applications to Two-Lane Rural Highways

HSM Applications to Two-Lane Rural Highways
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Predicting Crash Frequency and Applying CMF’s for Two-Lane Rural Highway Intersections - Session #6 Session #06 HSM Applications to Two-Lane Rural Highway Intersections Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Predicting Crash Frequency for Two-Lane Rural Highway Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Predicting Crash Frequency for Two-Lane Rural Highway Intersections Outcomes: Describe the SPF Base Models for prediction of Intersection Crash Frequency Calculate Predicted Crash Frequency for Rural Two-lane Highway Intersections Describe CMF’s for Rural 2 Lane Intersections Apply CMF’s to Predicted Crash Frequency Learning Outcomes for Session #8 for intersections Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Why Intersection Safety?
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Why Intersection Safety? A small part of overall highway system, but - In 2008 – 7,772 fatalities related to intersections (21% of Total Highway Fatalities) Each year more than 3.17 million intersection crashes occur (over 55% of all reported crashes) Key Message: Statistics on intersection crashes in the US. Est. Presentation Time: 1 min. Explanation of Cues/Builds: Lines build to allow instructor to first ask the question then provide the supporting facts Suggested Comments: Suggested Questions: none Additional Information: Although there is no inventory, it is estimated that there are approximately 3 million intersections in the US. About 2.7 million are unsignalized. Possible Problems: none Session 2 – Part I Fundamentals – Chapter 2 – User Needs

2008 US Total Crash Characteristics
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 2008 US Total Crash Characteristics Crash Type Total Crashes Fatal/Injury Crashes Number % Non Intersection 2,638,000 45% 722,680 43% Stop/No control Intersection 984,000 17% 321,520 19% Signalized Intersection 1,182,000 20% 380,511 23% Unclassified 1,005,000 240,306 14% Total 5,801,228 100% 1,637,476 37% 42% Source: USDOT Traffic Safety Facts 2008 Early Edition, A Compilation of motor vehicle crash data from FARS and GES, Table 29, Page 52 Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Physical vs Functional Area of an Intersection
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Physical vs Functional Area of an Intersection August 2010 From Final HSM, Chapter 10 14.3. DEFINITION OF AN INTERSECTION An intersection is defined as “the general area where two or more roadways join or cross, including the roadway and roadside facilities for traffic movements within the area”.(1) This chapter deals with at-grade intersections including signalized, stop controlled, and roundabout intersections. The definition of an intersection accident tends to vary between agencies.(5) Some agencies define an intersection accident as one which occurs within the intersection crosswalk limits or physical intersection area. Other agencies consider all accidents within a specified distance, such as 250-ft, from the center of an intersection to be intersection accidents.(5) However, not all accidents occurring within 250-ft of an intersection can be considered intersection accidents, since some of these may have An at-grade intersection is defined “by both its physical and functional areas”, as illustrated in Exhibit 14-1.(1) The functional area “extends both upstream and downstream from the physical intersection area and includes any auxiliary lanes and their associated channelization.”(1) As illustrated in Exhibit 14-2, the functional area on each approach to an intersection consists of three basic elements:(See Next Slide1) Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Functional Area of an Intersection
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Functional Area of an Intersection From Final HSM, Chapter 10 14.3. DEFINITION OF AN INTERSECTION The functional area “extends both upstream and downstream from the physical intersection area and includes any auxiliary lanes and their associated channelization.”(1) As illustrated in Exhibit 14-2, the functional area on each approach to an intersection consists of three basic elements:(1) 􀂃 Decision distance; 􀂃 Maneuver distance; and, 􀂃 Queue-storage distance. Decision Distance Maneuver Distance Queue-Storage Distance Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop
August 2010 Process for Prediction of Crash Frequency and Application of Crash Modification Factors Three Steps: 1. Predict Crash Frequency - Safety Performance Functions (SPF) Equations 2. Apply Appropriate Crash Modification Factors (CMFs) - Adjust predicted safety performance from base conditions to existing/proposed conditions - Are greater or less than 1: < lower crash frequency > increased crash frequency Calibration, Cr or Ci - Accounts for local conditions/data Safety Performance Functions Safety Performance Functions (SPFs) are regression equations that estimate the average crash frequency for a specific site type (with specified base conditions) as a function of annual average daily traffic (AADT) and, 770 in the case of roadway segments, the segment length (L). Base conditions are specified for each SPF and may include conditions such as lane width, presence or absence of lighting, presence of turn lanes etc. Calibration of Safety Performance Functions to Local Conditions The predictive models in Chapters 10, 11, and 12 have three basic elements, Safety Performance Functions, Accident Modification Factors and a calibration factor. The SPFs were developed as part of HSM-related research from the most complete and consistent available data sets. However, the general level of crash frequencies may vary substantially from one jurisdiction to another for a variety of reasons including crash reporting thresholds, and crash reporting system procedures. These variations may result in some jurisdictions experiencing substantially more reported traffic accidents on a particular facility type than in other jurisdictions. In addition, some jurisdictions may have substantial variations in conditions between areas within the jurisdiction (e.g. snowy winter driving conditions in one part of the state and only wet winter driving conditions in another part of the state). Therefore, for the predictive method to provide results that are reliable for each jurisdiction that uses them, it is important that the SPFs in Part C be calibrated for application in each jurisdiction. Methods for calculating calibration factors for roadway segments Cr and intersections Ci are included in the Part C Appendix to allow highway agencies to adjust the SPF to match local conditions. The calibration factors will have values greater than 1.0 for roadways that, on average, experience more accidents than the roadways used in developing the SPFs. Roadways that, on average, experience fewer accidents than the roadways used in the development of the SPF, will have calibration factors less than 1.0. The calibration factors, Cr and Ci, are based on the ratio of the total observed accident frequencies for a selected set of sites to the total expected average crash frequency estimated for the same sites, during the same time period, using the applicable Part C predictive method. Thus, the nominal value of the calibration factor, when the observed and predicted crash frequencies happen to be equal, is When there are more accidents observed than are predicted by the Part C predictive method, the computed calibration factor will be greater than When there are fewer accidents observed than are predicted by the Part C predictive method, the computed calibration factor will be less than 1.00. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

August 2010 Models to Predict Crash Frequency for Rural Two-Lane Highway Intersections Three-Approach Stop Control (Stop of Stem of Tee) Four-Approach Stop Control (2-way Stop) Four-Approach Signal Control This slide highlights the geometric features that have been studied and determined to influence the substantive safety of rural intersections. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

August 2010 SPF Models for RURAL Two-Lane Intersections with Stop Control on Minor-Road Three-Leg Stop Controlled Intersection (3ST): Nspf-3ST=exp[ ln(AADTmaj) ln(AADTmin)] Four-Leg 2-Way Stop Controlled Intersection (4ST): Nspf-4ST=exp[ ln(AADTmaj) ln(AADTmin)] From Final HSM, Chapter 10: Three-Leg Stop-Controlled Intersections The SPF for three-leg stop-controlled intersections is shown in Equation 10-8 and presented graphically in Exhibit 10-8: Nspf-3ST= exp[ ln(AADTmaj ) ln(AADTmin )] (Exhibit 10-8) Where, Nspf- 3ST = estimate of intersection-related predicted average crash frequency for base conditions for three-leg stop-controlled intersections; AADTmaj = AADT (vehicles per day) on the major road; AADTmin = AADT (vehicles per day) on the minor road. The overdispersion parameter (k) for this SPF is This SPF is applicable to an AADTmaj range from 0 to 19,500 vehicles per day and AADTmin range from 0 to 4,300 vehicles per day. Application to sites with AADTs substantially outside these ranges may not provide reliable results. Four-Leg Stop-Controlled Intersections The SPF for four-leg stop controlled intersections is shown in Equation 10-9 and presented graphically in Exhibit 10-9: Nspf-4ST = exp[ ln(AADTmaj)+0.61 ln(AADTmin )] (Exhibit 10-9) Nspf-4ST = estimate of intersection-related predicted average crash frequency for base conditions for four-leg STOP controlled intersections; The overdispersion parameter (k) for this SPF is This SPF is applicable to an AADTmaj range from 0 to 14,700 vehicles per day and AADTmin range from 0 to 3,500 vehicles per day. Application to sites with AADTs substantially outside these ranges may not provide accurate results. AADTmaj = Avg Annual Daily Volume on Major Road (veh/day) AADTmin = Avg Annual Daily Volume on Minor Road (veh/day) Predicting Highway Safety for Intersections on 2-Lane Rural Highways

SPF Models for RURAL Signalized Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 SPF Models for RURAL Signalized Intersections Four-Leg Signalized Intersection (4SG): Nspf-4SG = exp[ ln(AADTmaj) ln(AADTmin)] Nspf-4SG = estimate of intersection-related predicted average crash frequency for base conditions; From Final HSM Chapter 10: Four-Leg Signalized Intersections The SPF for four-leg signalized intersections is shown below and presented graphically in Exhibit 10-10: Nspf-4SG = exp[ ln(AADTmaj) ln(AADTmin )] (Exhibit 10-10) Where, Nspf-4SG = SPF estimate of intersection-related predicted average crash frequency for base conditions; AADTmaj = AADT (vehicles per day) on the major road; AADTmin = AADT (vehicles per day) on the minor road. The overdispersion parameter (k) for this SPF is This SPF is applicable to an AADTmaj range from 0 to 25,200 vehicles per day and AADTmin range from 0 to 12,500 vehicles per day. For instances when application is made to sites with AADT substantially outside these ranges, the reliability is unknown. AADTmaj = Avg Annual Daily Volume on Major Road (veh/day) AADTmin = Avg Annual Daily Volume on Minor Road (veh/day) Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Base Conditions for Rural Two-Lane Intersections:
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Base Conditions for Rural Two-Lane Intersections: Intersection Skew Angle: odegrees Presence of Left-Turn Lanes: none Presence of Right-Turn Lanes: none Lighting: none Key Message:These are the nominal geometry or base conditions represented by the base models. Additional Info: The reason for selecting these dimensions as the base conditions is statistical; it is not that these are the “safest.” The statistical reasons for these dimensions are: (1) they are (approximately) the mean values for these variables in the database used to fit the base model, and (2) regression model estimates have the least standard error near the mean values of the independent variables in the model. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

SPF Model for RURAL Stop Controlled Intersection– Example:
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 SPF Model for RURAL Stop Controlled Intersection– Example: 1-Way STOP on Minor Approach to a “T” Intersection (3-leg): For a 1-Way STOP with an AADT of 5000 across the top of the “T” on the main Road and 500 AADT on the minor road of the “T”, What is the predicted # of Crashes? Discussion Example Slide: Ask the workshop participants how they would go about making a prediction as to the intersection crashes for this T intersection with stop control of the stem of the T intersection. What “models” are available? How would apply this model? Predicting Highway Safety for Intersections on 2-Lane Rural Highways

SPF Model for RURAL Stop Controlled Intersection– Example:
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 SPF Model for RURAL Stop Controlled Intersection– Example: Three-Leg Stop Controlled Intersection (3ST): Nspf-3ST = exp[ ln(AADTmaj) ln(AADTmin)] For AADTmaj = 5,000 and AADTmin = 500: Nspf-3ST = exp[ ln(5,000) ln(500)] = exp[ ] Three-Leg Stop Controlled Intersection example = exp[-0.086] = crashes per year or 4.59 crashes in a 5 year period Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Safety Performance Function (SPF)
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Safety Performance Function (SPF) August 2010 Highway Safety Manual Approach: “one rate” Average Crash Rate Rather than “one” rate as with Crash Rate, the Highway Safety Manual SPF’s better conform to the observed Crash Frequency based upon exposure. Session 2 – Predicting Highway Safety for Multilane Rural Highway Segments

“Is this a Higher Crash Frequency Site?”
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop “Is this a Higher Crash Frequency Site?” August 2010 Highway Safety Manual Approach: “Substantive Crash Frequency” 6 crashes/yr “Difference” Instructor: discussion as the meaning of being “below” the predicted crash Frequency curve or being “above” the curve “Predicted Crash Frequency” 1.2 crashes/yr 0.5 crashes/yr Session 2 – Predicting Highway Safety for Multilane Rural Highway Segments

SPF Base Model for RURAL Signalized Intersection - Exercise
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 SPF Base Model for RURAL Signalized Intersection - Exercise 4-Approach Signalized Intersection: For a 4-Approach signalized intersection with AADT = 9,000 on the major road and AADT = 4,500 on the minor road, What is the predicted # of Crashes? Discussion Exercise Slide: Ask the workshop participants how they would go about making a prediction as to the intersection crashes for a signalized intersection with 4 approaches. What “models” are available? How would apply this model? Predicting Highway Safety for Intersections on 2-Lane Rural Highways

SPF Base Model for RURAL Signalized Intersection – Example:
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 SPF Base Model for RURAL Signalized Intersection – Example: 4-Approach Signalized Intersection: Nspf-4SG = exp[ ln(AADTmaj) ln(AADTmin)] For range of AADTmaj from zero to 25,200 and AADTmin from zero to 12,500 For AADTmaj = 9,000 and AADTmin = 4,500: Exercise calculation for a four-leg signalized intersection. Calculated value is similar to stop-control for lower AADT, see previous example. However, for higher AADT’s the difference between expected crashes for signalized intersections will grow higher than stop-controlled intersections. This is near the value if a signal warrant, thus the closeness in expected crash frequency with the previous prediction for a 4-way stop-control intersection (i.e., 7.65 vs 7.5 crashes per year) Nspf-4SG = exp[ ln(9,000) ln(4,500)] = crashes per year Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Severity Index for all highways and streets
Safety and Operational Effects of Geometric Design Features for Two-Lane Rural Highways Workshop Severity Index for all highways and streets April 2009 Severity index (SI) is the ratio of crashes involving an injury or fatality to total crashes * From NCHRP 486 The Old way – Pre Highway Safety Manual Severity Index from this table from page 37 of NCHRP 486 is 32% SI for Roadway Segments and 40% for intersections ..however, Chapter 10 of the HSM provides “better” injury and fatal crash distribution by type of rural intersection control in Tables 10-5 and 10-6 Session 3 –Exercise I

Crash Severity for Rural 2-Lane Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Crash Severity for Rural 2-Lane Intersections Table 10-5 From Final HSM, Chapter 10: Tables 10-5 and 10-6 provide the default proportions for accident severity levels and collision types, respectively. These exhibits may be used to separate the accident frequencies from Equations 10-8 through into components by severity level and collision type. The default proportions for severity levels and collision types shown in these Tables may be updated based on local data for a particular jurisdiction as part of the calibration process described in the Appendix to Part C. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Default Distribution of Crash Types for Rural 2-Lane Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Table 10-6: Default Distribution for Collision Types and Manner of Collisions Default Distribution of Crash Types for Rural 2-Lane Intersections From Final HSM, Chapter 10 Highlighted/circled areas indicate default values for the highest percentage of collision types for 3-leg & 4-leg stop controlled intersections and 4-leg signalized intersections. Tables 10-5 and 10-6 provide the default proportions for accident severity levels and collision types, respectively. These exhibits may be used to separate the accident frequencies from Equations 10-8 through into components by severity level and collision type. The default proportions for severity levels and collision types shown in these Tables may be updated based on local data for a particular jurisdiction as part of the calibration process described in the Appendix to Part C. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Applying Severity Index to Rural Two-Lane Highway Intersections
Safety and Operational Effects of Geometric Design Features for Two-Lane Rural Highways Workshop April 2009 Applying Severity Index to Rural Two-Lane Highway Intersections Example: Two-way stop controlled 4-approach intersection with 9,000 AADT on Major and 4,500 AADT on minor; Fatal and Injury crashes are 5 of 9 total crashes a. Compute the actual Severity Index (SI) SI4st = Fatal + Injury Crashes = 5/9 = 0.55 Total Crashes Instructor: Compute the severity index for actual crash frequency performance of 5 inj and fatal crashes out of a total of 9 crashes = 0.55 Session 3 –Exercise I

Safety and Operational Effects of Geometric Design Features for Two-Lane Rural Highways Workshop May 2009 Applying Severity Index to Rural Two-Lane Highway Intersections Instructor: Using Table 10-5, the severity index for a 4-approach 2-2way stop controlled intersection is 43.1/100 or 0.43 b. Compute the Predicted Severity Index (SI) SI4st = Fatal + Injury Crashes = 43.1/100= 0.43 Total Crashes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Safety and Operational Effects of Geometric Design Features for Two-Lane Rural Highways Workshop April 2009 Applying Severity Index to Rural Two-Lane Highway Intersections Example: Two-way stop controlled 4-approach intersection with 9,000 AADT on Major and 4,500 AADT on minor; Fatal and Injury crashes are 5 of 9 total crashes a. Actual Severity Index (SI) = ? b. Predicted Severity Index (SI) = ? 0.55 0.43 Instructor: Now compare the actual crash serverity of 0.55 to the predicted (from Table 10-5) of The actual crash experience is more severe than the predicted value and there were 9 crashes in a year in comparison to predicted of 7.5. - Is the Actual Severity Index higher or lower than the Predicted Severity Index? Higher ? Session 3 –Exercise I

August 2010 Process for Prediction of Crash Frequency and Application of Crash Modification Factors Three Steps: 1. Predict Crash Frequency - Safety Performance Functions (SPF) Equations - Predict Crash Frequency for base conditions 2. Apply Appropriate Crash Modification Factors (CMFs) - Adjust predicted safety performance from base conditions to existing/proposed conditions - Are greater or less than 1: < lower crash frequency > increased crash frequency Calibration, Cr or Ci - Accounts for local conditions/data Safety Performance Functions Safety Performance Functions (SPFs) are regression equations that estimate the average crash frequency for a specific site type (with specified base conditions) as a function of annual average daily traffic (AADT) and, 770 in the case of roadway segments, the segment length (L). Base conditions are specified for each SPF and may include conditions such as lane width, presence or absence of lighting, presence of turn lanes etc. Calibration of Safety Performance Functions to Local Conditions The predictive models in Chapters 10, 11, and 12 have three basic elements, Safety Performance Functions, Accident Modification Factors and a calibration factor. The SPFs were developed as part of HSM-related research from the most complete and consistent available data sets. However, the general level of crash frequencies may vary substantially from one jurisdiction to another for a variety of reasons including crash reporting thresholds, and crash reporting system procedures. These variations may result in some jurisdictions experiencing substantially more reported traffic accidents on a particular facility type than in other jurisdictions. In addition, some jurisdictions may have substantial variations in conditions between areas within the jurisdiction (e.g. snowy winter driving conditions in one part of the state and only wet winter driving conditions in another part of the state). Therefore, for the predictive method to provide results that are reliable for each jurisdiction that uses them, it is important that the SPFs in Part C be calibrated for application in each jurisdiction. Methods for calculating calibration factors for roadway segments Cr and intersections Ci are included in the Part C Appendix to allow highway agencies to adjust the SPF to match local conditions. The calibration factors will have values greater than 1.0 for roadways that, on average, experience more accidents than the roadways used in developing the SPFs. Roadways that, on average, experience fewer accidents than the roadways used in the development of the SPF, will have calibration factors less than 1.0. The calibration factors, Cr and Ci, are based on the ratio of the total observed accident frequencies for a selected set of sites to the total expected average crash frequency estimated for the same sites, during the same time period, using the applicable Part C predictive method. Thus, the nominal value of the calibration factor, when the observed and predicted crash frequencies happen to be equal, is When there are more accidents observed than are predicted by the Part C predictive method, the computed calibration factor will be greater than When there are fewer accidents observed than are predicted by the Part C predictive method, the computed calibration factor will be less than 1.00. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

August 2010 HSM Crash Modification Factors for Rural Two-Lane Highway Intersections Configuration - Number of Legs Intersection Designs - Roundabouts Angle of Intersection (Skew) Left Turn Lanes Right Turn Lanes Lighting This slide highlights the geometric features that have been studied and determined to influence the substantive safety of rural intersections. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Potential Conflict Points
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Comparison of 4-leg/3-leg Intersections August 2010 Cross intersection has 32 conflict points, Offset T has 22 points Potential Conflict Points As illustrated, the number of conflict locations is reduced by 10 for the 2x2-lanes or the 2x4-lanes crossings from 40 to 30 locations. It is generally recognized that 4-leg intersections produce a more efficient roadway network. We generally strive for a system comprised of a grid in which most intersections are 4-leg. This minimizes travel time and reduces the number of intersections in the system. One should note, though, that in terms of conflicts, 4-leg intersections present a significantly greater risk than 3-leg intersections. (The instructor may need to briefly explain through use of a whiteboard, overhead or pad the types of conflicts -- crossing, diverging, merging). Kuciemba and Cirillo (1991) reviewed the safety implications of T and Y-intersections in rural municipalities in the U.S. Of 500 intersections analyzed, it was found that the collision rate for T-intersections was 34 percent lower than for Y-intersections (1.22 collisions per million entering vehicles for Y-intersections versus 0.80 for T-intersections). Session 5 – Intersection Geometrics & Countermeasures

Number of Intersection Legs
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Number of Intersection Legs Crash Frequency for intersections with only 3 approaches is lower Crash Frequency for intersections with 4 approaches are greater than for those intersections with only 3 approaches Collision rates for intersections with more than 4 approaches are 2 to 8 times greater than for 4 approach Intersections Collision rates for intersections with more than 4 approaches are 2 to 8 times greater than for 4 approach Intersections Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Rural Intersection Skew Angle
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Rural Intersection Skew Angle Some studies (McCoy, for example) show adverse effect of skew Skews increase exposure time to crashes; increase difficulty of driver view at stopped approach @ 90 degrees Skew Angle Intersection Angle = 350 Instructor should point out that research on older drivers shows they tend to have difficulty in moving their head to look to the side; hence skewed intersections represent particular difficulties to them. Intersection angles that are close to 90o are considered safer than severely acute and obtuse angles. Modern design guidelines tend to limit intersection angles to 70o (110o) or better. The findings of the literature review on this topic are summarized as follows: · Staplin et al. (2001), in the Highway Design Handbook for Older Drivers and Pedestrians state that “decreasing the angle on the intersection makes detection of and judgments about potential conflicting vehicles on crossing roadways much more difficult”. They indicate that skewed intersections pose particular problems for older drivers due to the decline in head and neck mobility which usually accompanies advancing age. ITE (1999) states that “crossing roadways should intersect at 90 degrees if possible, and not less than 75 degrees." It further states that: "Intersections with severe skew angles (e.g., 60 degrees or less) often experience operational or safety problems. Reconstruction of such locations or institution of more positive traffic control such as signalization is often necessary.“ Regarding intersection design issues on two-lane rural highways, ITE (1999) states that: "Skew angles in excess of 75 degrees often create special problems at stop-controlled rural intersections. The angle complicates the vision triangle for the stopped vehicle; increases the time to cross the through road; and results in a larger, more potentially confusing intersection." Skew = 900 – 350 = 550 SKEW = Intersection Skew Angle (degrees) as the absolute value of the difference between 90 degrees and the actual intersection angle Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Intersection Skew Angle (CMF1i)
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Intersection Skew Angle (CMF1i) For 3- legged Stop Controlled Intersections: CMF1i = exp ( SKEW) For 4- legged Stop Controlled Intersections: CMF1i = exp ( SKEW) SKEW = Intersection Skew Angle (degrees) as the absolute value of the difference between 90 degrees and the actual intersection angle For signalized intersections, the CMF for skew is always 1.00 per Final Draft of the HSM: Four-leg Signalized Intersections -- Since the traffic signal separates most movements from conflicting approaches, the risk of collisions related to the skew angle between the intersecting approaches is limited at a signalized intersection. Therefore, the CMF for skew angle at four-leg signalized intersections is 1.00 for all cases. CMF1i - Intersection Skew Angle The base condition for intersection skew angle is 0 degrees of skew (i.e., an intersection angle of 90 degrees). The skew angle for an intersection was defined as the absolute value of the deviation from an intersection angle of 90 degrees. The absolute value is used in the definition of skew angle because positive and negative skew angles are considered to have similar detrimental effect(4). This is illustrated in Chapter 14 Section Older Driver Handbook, 2001, Intersections, Recommendation A. (2). “In the design of new facilities or redesign of existing facilities where right-of-way is restricted, intersecting roadways should meet at an angle of not less than 75 degrees.” (3).“At skewed intersections where the approach leg to the left intersects the driver’s approach leg at an angle of less than 75 degrees, the prohibition of right turn on Red (RTOR) is recommended”. – not in current MUTCD nor in Rev#2. *NCHRP 500, Strategy 17.1 B16 – Realign Intersection Approaches Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Intersection Skew Angle (CMF1i) Intersection Skew from 90 degree side road for 4-leg Approaches Skew= CMF = *Max skew of 15 degrees - Older Driver Handbook and ITE Max skew of 30 degrees – 2004 Green Book A panel of experts recently reviewed the literature and established these crash modification factors for improving intersection skew, from FHWA-RD (page 43) and TTI Report, Roadway Safety Design Synthesis, November 2005, page 6-29. Older Driver Handbook, 2001, Intersections, Recommendation A. (2). “In the design of new facilities or redesign of existing facilities where right-of-way is restricted, intersecting roadways should meet at an angle of not less than 75 degrees.” (3).“At skewed intersections where the approach leg to the left intersects the driver’s approach leg at an angle of less than 75 degrees, the prohibition of right turn on Red (RTOR) is recommended”. – not in current MUTCD nor in Rev#2. ITE states that “Skewed intersections should be avoided, and in no case should the angle be less than 75 degrees,” and further states “Intersections with severe skew angles (e.g., 60 degrees or less) often experience operational or safety problems.” Intersection Design (2004 AASHTO GreenBook, page 388) - ……The driver of a vehicle approaching an intersection should have an unobstructed view of the entire intersection and sufficient lengths of the intersecting roadways to permit the driver to anticipate and avoid potential collisions. Sight distances at intersections with six different types of traffic control are presented in Chapter 9. Intersections should be designed with a corner radius of the pavement or surfacing that is adequate for a selected design vehicle, representing a larger vehicle that is anticipated to use the intersection with some frequency. For minimum edge radius, see Chapter 9. Where turning volumes are significant, consideration should be given to speed change lanes and channelization. Intersection legs that operate under stop control should intersect at right angles wherever practical, and should not intersect at an angle less than 60 degrees. For further details, see Chapter 9. *NCHRP 500, Strategy 17.1 B16 – Realign Intersection Approaches Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Intersection Skew Angle (CMF1i) Example: #1 –90 deg Skew = 15 CMF1i = e0.0040(15) =1.062 #2 –45 deg #3 –80 deg #4 –75 deg Skew = 0 CMF1i = 1.000 Skew = 45 CMF1i = e0.0054(45) =1.275 Skew = 10 CMF1i = e0.0040(10) =1.041 Exercise for participants to use their knowledge of safety effect of skew angle Intersection #1 at 90 degrees (Skew angle = 90-90=0) has CMF of 1.0 Intersection #2 (4-legged) at 45 degrees(skew angle = 90-45=45) has CMF of 1.275 Intersection #3 (3-legged) at 80 degrees (skew angle =90-80=10) has CMF of Intersection #4 (3-legged) at 75 degrees (skew angle = 90-75=15) has CMF of For each of the four (4) intersections, calculate the safety effect of skew angle Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Solutions to Skewed Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 New Alignment Old Alignment *NCHRP 500, Strategy 17.1 B16 – Realign Intersection Approaches Design improvements to skewed geometry may involve realignment of the approaches, or separating the single intersection into two T-type intersections. Photo lower left from Washington State; upper left from northeast Illinois DOTs purchases strip parcels to reconstruct the intersection at no, or greatly reduced, skew angle. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Solutions to Skewed Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Locate Intersection at Mid-Point of Curve Location of intersection at the mid-point of a curve Reduces Skew and maximizes sight distance of approaching traffic Upper left photo from northeast Illinois; lower right from Mn near St. Paul *NCHRP 500, Strategy 17.1 B16 – Realign Intersection Approaches Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Left Turn Lanes in the Rural Highway Environment
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Left Turn Lanes in the Rural Highway Environment Left turn lanes remove stopped traffic from through lanes mitigate rear-end conflict enable selection of safe gap The advantages of left turn lanes in the rural environment are primarily safety versus capacity. The design of left turn lanes in the rural environment should be based on the deceleration requirements. This differs from the higher volume urban environment in which queuing and storage generally drive design of left turn lanes. Location of illustrative photo is Illinois route 125 east of Beardstown for left turn lanes at a new intersection in the middle of a curve alignment improvement project. Add in warrants of turn lanes in the rural environment from NCHRP 457 Bonneson warrants for turn lanes in the rural environment see NCHRP 457 “Capacity” is generally not the issue *NCHRP 500, Strategy 17.1 B1 – Provide Left-Turn Lanes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Left Turn Lanes (CMF2i)
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Left Turn Lanes (CMF2i) ____ From Final SM: CMF2i - Intersection Left-Turn Lanes The base condition for intersection left-turn lanes is the absence of left-turn lanes on the intersection approaches. The CMFs for the presence of left-turn lanes are presented in Exhibit These CMFs apply to installation of left-turn lanes on any approach to a signalized intersection, but only on uncontrolled major road approaches to a stop-controlled intersection. The CMFs for installation of left-turn lanes on multiple approaches to an intersection are equal to the corresponding CMF for the installation of a left-turn lane on one approach raised to a power equal to the number of approaches with left-turn lanes. There is no indication of any safety effect of providing a left-turn lane on an approach controlled by a stop sign, so the presence of a left-turn lane on a stop-controlled approach is not considered in applying Exhibit The CMFs for installation of left-turn lanes are based on research by Harwood et al.(4) and are consistent with the CMFs presented in Chapter 14. An CMF of 1.00 is always be used when no left-turn lanes are present. From TechBrief FHWA-RD , November 2002 and NCHRP 500, Objective 17.1 B Reduce the Frequency and Severity of Intersection Conflicts through Geometric Design Improvements additional research to assess the safety effectiveness of left-turn lanes at unsignalized intersections has been conducted for FHWA by Midwest Research Institute (MRI) (Harwood et al., 2002). MRI performed an extensive before-after evaluation of added turn lanes at intersections and found that added left-turn lanes are effective in improving safety at unsignalized intersections in both rural and urban areas. Installation of a single left-turn lane on a major-road approach would be expected to reduce total intersection accidents at rural unsignalized intersections by 28 percent for four-legged intersections and by 44 percent for three-legged intersections. At urban unsignalized intersections, installation of a left-turn lane on one approach would be expected to reduce total accidents by 27 percent for four-legged intersections and by 33 percent for three legged intersections. Installation of left-turn lanes on both major-road approaches to a four-legged intersection would be expected to increase, but not quite double, the resulting effectiveness measures for total intersection accidents. NCHRP 500, Strategy 17.1 B1 – Provide Left-Turn Lanes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Rural Left Turn By-Pass Lanes
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Rural Left Turn By-Pass Lanes Less cost than conventional left turn lane At low volume intersections, may be just as effective Minnesota study unable to conclude bypass lanes just as safe as left turn lanes Left turn bypass lanes have negative offset for the left turn lane and there is motorist confusion as will the driver in the left lane turn or go through. Information from slide is direct quote from Howard Preston safety report to MnDot Strategy 17.1 B4—Provide Bypass Lanes on Shoulders at T-Intersections (T) General Description At three-legged intersections on two-lane highways, shoulder bypass lanes can provide an effective substitute for a left-turn lane on the major road where provision of a left-turn lane is economically infeasible. Instead of providing a left-turn lane for drivers turning left from the major road, part of the shoulder may be marked as a travel lane to encourage following through drivers to use this shoulder lane to bypass vehicles waiting to turn left. This treatment involves substantially less cost than providing a conventional left-turn lane and, at low-volume intersections, it may be just as effective. Minnesota evaluated the operational and safety effects of using bypass lanes at rural intersections by comparing the operational and safety characteristics of rural intersections without turning lanes, with bypass lanes, and with left-turn lanes (Preston and Schoenecker, 1999a). Based upon a comparative crash analysis and a before-after evaluation, Minnesota was unable to conclude that the use of a bypass lane provides a greater degree of safety when compared with intersections without a bypass lane or a left-turn lane. However, Nebraska has reported a marked decrease in rear-end collisions at shoulder bypass lanes, and other states have reported relatively few accidents occurring at shoulder bypass lane installations (Sebastian and Pusey, 1982). Additional evaluations are necessary to sufficiently quantify the safety effectiveness of bypass lanes on shoulders. A key to success is providing a shoulder area for the bypass lane that has sufficient structural strength to withstand repeated usage, even by trucks. There may be an upper limit of traffic volumes above which shoulder bypass lanes should not be used. No such limit has been quantified, but highway agencies should still consider carefully the appropriateness of shoulder bypass lanes on high-volume two-lane roads. Shoulder bypass lanes should not be viewed as a substitute for conventional left-turn lanes as part of a reconstruction or major redesign project where right-of-way is available and construction feasible. *NCHRP 500, Strategy 17.1 B4 – Provide By-Pass Lanes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

August 2010 CMF for Right Turn Lanes (CMF3i) Right turn lanes remove slowing traffic from through lanes which are not stop controlled “Capacity” is generally not the issue *NCHRP 500, Strategy 17.1 B6 – Provide Right-Turn Lanes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

August 2010 CMF for Right Turn Lanes (CMF3i) ____ From Final HSM, Chapter 10:The base condition for intersection right-turn lanes is the absence of right-turn lanes on the intersection approaches. The CMF for the presence of right-turn lanes is based on research by Harwood et al.(4) and is consistent with the CMFs in Chapter 14. These CMFs apply to installation of right-turn lanes on any approach to a signalized intersection, but only on uncontrolled major road approaches to stop-controlled intersections. The CMFs for installation of right-turn lanes on multiple approaches to an intersection are equal to the corresponding CMF for installation of a right-turn lane on one approach raised to a power equal to the number of approaches with right-turn lanes. There is no indication of any safety effect for providing a right-turn lane on an approach controlled by a stop sign, so the presence of a right-turn lane on a stop-controlled approach is not considered in applying Exhibit The CMFs in the exhibit apply to total intersection accidents. An CMF value of 1.00 is always be used when no right-turn lanes are present. This CMF applies only to right-turn lanes that are identified by marking or signing. The CMF is not applicable to long tapers, flares, or paved shoulders that may be used informally by right-turn traffic. From TechBrief FHWA-RD , November 2002 and NCHRP 500, Strategy 17.1 B6 – Provide Right turn Lanes at Intersections General Description Many collisions at unsignalized intersections are related to right-turn maneuvers. A key strategy for minimizing such collisions is to provide exclusive right-turn lanes, particularly on high-volume and high-speed major-road approaches (Exhibit V-10). Right-turn lanes remove slow vehicles that are decelerating to turn right from the through-traffic stream, thus reducing the potential for rear-end collisions. Additional research to assess the safety effectiveness of right-turn lanes at unsignalized intersections has been conducted for FHWA by Midwest Research Institute (MRI) (Harwood et al., 2002). MRI performed an extensive before-after evaluation of adding turn lanes at intersections and found that added right-turn lanes are effective in improving safety at rural unsignalized intersections. Installation of a single right-turn lane on a major-road approach would be expected to reduce total intersection accidents at rural unsignalized intersections by 14 percent. Installation of right-turn lanes on both major-road approaches to a four-legged intersection would be expected to increase, but not quite double, the resulting effectiveness measures for total intersection accidents. MRI also found that right-turn lane installation reduced accidents on individual approaches to four-legged intersections by 27 percent at rural unsignalized intersections. NCHRP 500, Strategy 17.1 B6 – Provide Right Turn Lanes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Lighting of Rural 2-Lane Intersections (CMF4i)
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Lighting of Rural 2-Lane Intersections (CMF4i) CMF4i = pni From Final HSM: CMF4i - Lighting The base condition for lighting is the absence of intersection lighting. The CMF for lighted intersections is adapted from the work of Elvik and Vaa (1), as: CMF4i = × pni (Exhibit 10-24) Where, CMF4i = Accident Modification Factor for the effect of lighting on total accidents; pni = proportion of total accidents for unlighted intersections that occur at night. This CMF applies to total intersection accidents. Exhibit presents default values for the nighttime accident proportion pni. HSM users are encouraged to replace the estimates in Exhibit with locally derived values. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Lighting of Rural 2-Lane Intersections (CMF4i) – Example:
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Lighting of Rural 2-Lane Intersections (CMF4i) – Example: For 4 approach Two-Way Stop Controlled rural intersection: CMF4i = pni = (0.244) Example for calculating CMF for lighting. = 0.907 NCHRP 500, Strategy 17.1 E2-Improve Visibility of Intersection by Providing Lighting (P) Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Additional CMF’s from Part D and Research
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Additional CMF’s from Part D and Research Beyond the SPF’s and CMF’s detailed in Part C Chapter 10: CMF’s for Roundabouts from Chapter 14 CMF for 4-Way Stop CMF for STOP AHEAD Pavement marking CMF for STOP Beacons CMF for driveways within 250 feet from TTI Research Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Roundabouts are Alternatives to conventional intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Roundabouts are Alternatives to conventional intersections Number of conflicts is reduced Severe conflicts (angle) are eliminated Speed differentials are reduced or eliminated Roundabouts have been recently highlighted through research sponsored by FHWA as important improvements to conventional intersections. The instructor may wish to point out that FHWA has a course that teaches the Roundabout informational Guide. *NCHRP 500, Strategy 17.2 B5 – Construct Special Solutions – Roundabout Design Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF’s for Conversion of 2-Way Stop Intersection to Roundabout
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF’s for Conversion of 2-Way Stop Intersection to Roundabout Convert Signalized Intersection to a Modern Roundabout Roundabouts reduce traffic speeds as a result of their small diameters, deflection angle on entry, and circular configuration. Roundabouts also change conflict points from crossing conflicts to merging conflicts. Their circular configuration requires vehicles to circulate in a counterclockwise direction. The reduced speeds and conflict points contribute to the crash reductions experienced compared to signalized intersections. The reduced vehicle speeds and motor vehicle conflicts are the reason roundabouts are also considered as a traffic calming treatment for locations experiencing characteristics such as higher than desired speeds and/or cut through traffic. The base condition for the CMFs shown in Exhibit 14-4 (i.e., the condition in which the CMF = 1.00) is a stop-controlled intersection. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Roundabouts in the rural environment
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Roundabouts in the rural environment *NCHRP 500, Strategy 17.1 F3 – Provide Roundabouts Before After Roundabouts provide an important alternative to signalized and all-way stop-controlled intersections. Modern roundabouts differ from traditional traffic circles in that they operate in such a manner that traffic entering the roundabout must yield the right-of-way to traffic already in it. Roundabouts can serve moderate traffic volumes with less delay than signalized or all-way stop-controlled intersections because traffic can normally traverse the roundabout without stopping. Suggested Questions: ASK the class who has had experience installing roundabouts. If none, how about driving through roundabouts? Additional Information: This is located in University Place, Washington Possible Problems: none CMF (single lane) = 0.29 CMF (multi-lane) = 0.56 Converting Stop-Control to Roundabout Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Roundabouts in the rural environment
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Roundabouts in the rural environment Single Lane Rural Roundabout: Approach speed limits 45 mph, 60 foot right of way Before Crash Info – 2 yrs: - 12 crashes with 4 F/Inj Roundabouts provide an important alternative to signalized and all-way stop-controlled intersections. Modern roundabouts differ from traditional traffic circles in that they operate in such a manner that traffic entering the roundabout must yield the right-of-way to traffic already in it. Roundabouts can serve moderate traffic volumes with less delay than signalized or all-way stop-controlled intersections because traffic can normally traverse the roundabout without stopping. Suggested Questions: ASK the class who has had experience installing roundabouts. If none, how about driving through roundabouts? Additional Information: This is located in University Place, Washington Possible Problems: none After Crash Info – 2 yrs: - 4 crashes with 0 F/Inj Summit County Ohio Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF’s for Conversion of 2-Way Stop to All-Way Stop Control
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF’s for Conversion of 2-Way Stop to All-Way Stop Control From Final HSM: Convert Minor-Road Stop Control to All-way Stop Control The Manual on Uniform Traffic Control Devices (MUTCD) contains warrants to determine when it is appropriate to convert an intersection with minor-road stop control intersection to an all-way stop control intersection. The effects on crash frequency described below assume that MUTCD warrants for converting a minor road stop-controlled intersection to an all-way stop-control intersection are met. Urban and rural minor-road stop-controlled intersections Exhibit 14-9 provides specific information regarding the crash effects of converting urban intersections with minor-road stop control to all-way stop control when established MUTCD warrants are met. The effect on pedestrian crashes is also shown in Exhibit 14-9. The base condition for the CMFs below (i.e., the condition in which the CMF = 1.00) is an intersection with minor-road stop control that meets MUTCD warrants to become an all-way stop controlled intersection. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF’s for STOP AHEAD Supplementary Pavement Marking
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF’s for STOP AHEAD Supplementary Pavement Marking Predicting Highway Safety for Intersections on 2-Lane Rural Highways

August 2010 CMF’s for Beacons Table 14-42 Four approach, STOP control, Two lane roads Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Driveway near Rural Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Driveway near Rural Intersections Access points within 250 feet upstream and downstream of an intersection are undesirable Unsignalized - 20% more crashes for 3 driveways within 250 feet Signalized - 13% more crashes for 3 driveways within 250 feet Consolidate multiple access points Relocate access to the adjacent side road if possible Driveway density in the close proximity of intersections is not addressed (quantified) in the first edition of the HSM. However due to the known relationship of crash frequency (higher) in the vicinity of intersections with high access density this is TTI Roadway Safety Design Synthesis (TTI P1) 2005 NCHRP 500, 2003 Objective 17.1A FHWA Access Management in the Vicinity of Intersections FWHA-SA February 2010 Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Access Control for Rural Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Access Control for Rural Intersections *From TTI Roadway Safety Design Synthesis, 2005) Unsignalized Intersections: CMFnd = e0.056 * (dn-3) Signalized Intersections: CMFnd = e0.046 * (dn- 3) Where: dn = Number of driveways on both the major and minor road approaches within 250 feet of the intersection From Chapter 6 (pg 6-20) of TTI Roadway Safety Design Synthesis (TTI P1) 2005 Predicting Highway Safety for Intersections on 2-Lane Rural Highways

CMF for Access Control for Rural Intersections: Example Calculation
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 CMF for Access Control for Rural Intersections: Example Calculation *From TTI Roadway Safety Design Synthesis, 2005) Unsignalized Intersections: For 4 driveways on US route and 3 driveways on County Route CMFnd = e0.056 (dn - 3) = e0.056 (7 - 3) = e0.056 (4) Example calculation for Access Control = 1.25 Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Additional Low Cost Safety Measures beyond the published 2010 HSM
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Additional Low Cost Safety Measures beyond the published 2010 HSM Beyond the Highway Safety Manual are many proven low cost safety measures Additional low cost safety measures in addition to those published in the 2010 HSM. htpp:// Predicting Highway Safety for Intersections on 2-Lane Rural Highways

2009 MUTCD Figure 2A-4 Intersection Typical Signing
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 2009 MUTCD Figure 2A-4 Intersection Typical Signing Regulatory Right-of-Way Guide Warning First is warning, then guide signing, then regulation (regulatory) at the intersection. Spreading the information and getting drivers in the appropriate lanes is essential. Applying the two guiding principles of: - Clarify and Simplify Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Applying Simplify and Clarify
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Applying Simplify and Clarify Warning Guide Regulatory Right-of-Way First is warning, then guide signing, then regulation (regulatory) at the intersection Applying the two guiding principles of: Clarify and Simplify Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Low Cost Intersection Safety Measures – Signing Countermeasures
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 1.Warning First is warning, then guide signing, then regulation (regulatory) at the intersection. All-Way Stop of 2 rural State Highways CMF = 0.60 Rural CMF = 0.70 Urban Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Low Cost Intersection Safety Measures – Signing Countermeasures August 2010 2. Enhanced Warning First is warning, then guide signing, then regulation at the intersection All-Way Stop of 2 rural State Highways “Double-Up” CMF = 0.69 Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Low Cost Intersection Safety Measures – Signing Countermeasures August 2010 3. Enhanced Warning First is warning, then guide signing, then regulation at the intersection All-Way Stop of 2 rural State Highways Warning Beacons CMF = 0.75 Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 4. Advance Guide Signs First is warning, then guide signing, then regulation (regulatory) at the intersection. All-Way Stop of 2 rural State Highways Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Low Cost Intersection Safety Measures – Signing Countermeasures August 2010 5. Regulatory Right-of-Way Stop Sign on outside of large right turn radius is too far out of center attention window of driver First is warning, then guide signing, then regulation (regulatory) at the intersection All-Way Stop of 2 rural State Highways Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Low Cost Intersection Safety Measures – Signing Countermeasures August 2010 5. Regulatory Right-of-Way Add Stop Sign on Island to Enhance Visibility CRF = 11% + Right Hand Supplementary Stop Sign First is warning, then guide signing, then regulation at the intersection All-Way Stop of 2 rural State Highways Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Low Cost Intersection Safety Measures – Signing Countermeasures August 2010 6. Regulatory Right-of-Way “Double Up” Stop Signs CMF = 0.89 First is warning, then guide signing, then regulation (regulatory) at the intersection. CRF = 11% total crashes CRF = 55% Rt Angle Crashes Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop Low Cost Intersection Safety Measures – Signing Countermeasures August 2010 7. STOP Beacon Add Stop Beacon CMF = 0.42 angle crashes First is warning, then guide signing, then regulation (regulatory) at the intersection. All-Way Stop of 2 rural State Highways Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Install Splitter Islands on the Minor Road Approach to an Intersection 9. Splitter Island “Call Attention” to the presence of the Intersection *NCHRP 500, Strategy 17.1 E3 – Install Splitter Islands on Minor Road Approaches Location is the intersection of two rural state routes, IL 104 with US 67 in central Illinois. T-Intersection in rural area; 2003 ADT's on north approach = 2550, South approach = 3950, and west approach = 3200; continuing problem of traffic from the stem of T pulling out into path of turning traffic and through traffic across the head of the T;Crashes for 5-year period of are 4 crashes, all PD, all daytime Strategy 17.1 E3—Install Splitter Islands on the Minor-Road Approach to an Intersection (T) General Description Many unsignalized intersections are not visible to approaching drivers. Thus, intersection crashes may occur because one or more drivers may be unaware of the intersection. “Splitter” islands can be installed on minor-road approaches to call attention to the presence of the intersection and to guide traffic through the intersection. A splitter island refers to a channelizing island that separates traffic in opposing directions of travel, as opposed to islands that separate merging or diverging traffic in the same direction of travel. Splitter islands are particularly appropriate on approaches to skewed intersections. Effectiveness: Splitter islands are generally perceived to be effective in defining the presence of an intersection. When properly applied, they may reduce traffic speeds and intersection crashes, but there is no consensus on their effectiveness. CRF = 45% 3-Approach CRF = 40% 4-Approach Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Low Cost Intersection Safety Measures – Rumble Treatment
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Concept 1 – Narrow travel lanes by striping on Main highway Need speaker notes on the next few slides on “Concept 1 & 2” – get from Fred Narrow down lane width from 12 ft on the approach to 9 ft at the intersection. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Concept 1 – Narrow travel lanes by striping on Main highway Example from PA with the necked-down lanes (12’ on approaches to 9’ at the intersection). Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Concept 1 – Narrow travel lanes by striping on Main highway Effects of reducing the lane width of travel lanes from approaches to the intersections. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

after 2 years, total crash reduction = 32%
Safety and Operational Effects of Geometric Design Features for Two-Lane Rural Highways Workshop May 2009 after 2 years, total crash reduction = 32% Injury/Fatal crash reduction = 34% Effects of reducing the lane width of travel lanes from approaches to the intersections. Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Concept 2 – Add splitter Island on side road approaches Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Low Cost Intersection Safety Measures – Add Splitter Island with Stop on Centerline HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Concept 2 – Add splitter Island on side road approaches Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Predicting Crash Frequency for Two-Lane Rural Highway Intersections
HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Predicting Crash Frequency for Two-Lane Rural Highway Intersections Outcomes: Described the SPF Base Models for prediction of Intersection Crash Frequency Calculated Predicted Crash Frequency for Rural Two-lane Highway Intersections Described CMF’s for Rural 2 Lane Intersections Applied CMF’s to Predicted Crash Frequency Learning Outcomes for Session #8 for intersections Predicting Highway Safety for Intersections on 2-Lane Rural Highways

Questions and Discussion
Predicting Crash Frequency for Two-Lane Rural Highway Intersections HSM Practitioner's Guide for Two-Lane Rural Highways Workshop August 2010 Questions and Discussion Predicting Highway Safety for Intersections on 2-Lane Rural Highways

HSM Applications to Two-Lane Rural Highways

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