safety assessment of the intersection of davidson st and linwood st shun cheung

CE 7600 HIGHWAY SAFETY & RISK MANAGEMENT

COURSE PROJECT: CRASH ANALYSIS OF THE INTERSECTION AT DAVIDSON ST. W. & LINWOOD ST. DETROIT, MICHIGAN

Name: Shun Cheung ID Number: eo3413 April 18, 2013

Crash Analysis of the Intersection at Davidson Street West & Linwood Street

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TABLE OF CONTENTS

EXECUTIVE SUMMARY 2 INTRODUCTION 4 SITE DESCRIPTION 5 DATA COLLECTION 6 SUGGESTED COUNTERMEASURES 10 CONCLUSIONS & RECOMMENDATIONS 11 REFERENCES 13 TECHNICAL APPENDIX

TABLE OF FIGURES

FIGURE 1 - Map of Study Location 4 FIGURE 2 - Plan View (Intersection of Davidson St. W. & Linwood St. 5 FIGURE 3 - Northbound of Linwood St. 6 FIGURE 4 - Southbound of Linwood St. 6 FIGURE 5 - Eastbound of Davidson St. W. 6 FIGURE 6 - Westbound of Davidson St. W. 6 FIGURE 7 - A.M. Peak Hour Traffic Volumes in 2013 7 FIGURE 8 - P.M. Peak Hour Traffic Volumes in 2013 7 FIGURE 9 - Bar Chart of Crash by Type (2009 to 2011) 9 FIGURE 10 - Bar Chart of Time of Crash (2009 to 2011) 10

TABLE OF TABLES

TABLE 1 - Peak Hour Traffic Volumes for 2009 & Estimated 2013 7 TABLE 2- Spot Speed Study Table 8 TABLE 3 - Traffic Signal Timing Database 8 TABLE 4 - Traffic Signal Database 8 TABLE 5 - Roadway Database 8 TABLE 6 - Accident Pattern Table 11

APPENDIX

EXISTING CONDITION A Condition Diagram – Davidson St. W & Linwood St. A1

Condition Diagram – Davidson St. W & Linwood St. (With Improvements) A2 TRAFFIC VOLUMES B A.M. Peak Hour Traffic Volume Diagram B1

P.M. Peak Hour Traffic Volume Diagram B2 SAFETY ANALYSIS C

Collision Database (2010) C1 – C2 Collision Database (2011) C3 – C5 Collision Diagram (2010) C6 Collision Diagram (2011) C7


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EXECUTIVE SUMMARY Crashes could arise in many forms and situations that give drivers unexpected outcomes when they happen. The study of crash analysis is to attempt to minimize the existing crashes from happening and also any future events which could produce serious injuries or fatalities. Safety also involves a significant role to offer drivers a comfortable setting to travel from a starting point to the ending point. The study for this crash analysis project is for an intersection. The intersection chosen is located at Davidson Street West and Linwood Street in Wayne County, Michigan. The project combines the process of data collection, field observation, data analysis and countermeasure recommendations. The data collection portion of the project involves gathering the data for past traffic volumes and crash reports of the study intersection. For the past traffic volumes, the data was converted with a growth rate of 0.5% for the geographical area to present estimated current traffic volumes. From the projection by the growth rate, the traffic volumes had a minor increase to the overall volumes. With such information, the analyst could develop turning movement diagrams for future analysis. And for the crash reports, the analyst reviewed the past three years of occurrence and use the data to create collision diagrams. For the field observation segment of the project, spot speed study was performed using a video recording camera to capture the traffic activities and then reviewed the footages. A sample of 100 vehicles were selected for the study without differentiating by vehicle types. The purpose of the study is to locate the mean speed and the operating speed during the observed period. Those two variables represent the 50th and 85th percentiles of the speed distribution to examine if the posted speed requires any adjustment. Through the study, the overall sample of vehicles did not exceed the 5 mph deviation of the current posted speed. It is acceptable to maintain the current speed limit with no adjustment required. In the data analysis section of the project, it was revealed that the annual average of 30 crashes was the same for the two year period and also the three year period. Also using the collision diagrams of the past two years, it was shown that a majority of those crashes were related to left-turn head-on, rear-ended and angle. The left-turn head-on collisions occurred when vehicles attempting to turn to driveways of the opposing side of the road to reach to restaurants or gas stations. The rear-end collisions were situated mostly stopping for red signal at the intersection and angle collisions were concentrated at the inside of the intersection when drivers violating the stopping for the red light. Once the concept of the causes of collisions were established, the construction of accident pattern table could be used to record the causes and countermeasures of the collisions to provide basic ideas to conclude on a more specific countermeasures designed for the intersection. One of the major causes of collision at the intersection was left-turn head-on. To reduce the left-turn head-on problem, installation of raised median islands on north, south, east and west legs of the intersection would prevent drivers to access to driveways from the opposing direction. With the decrease in width of roadway taken up by the median, a reduction on the lane width from 12 ft. to 11 ft. is necessary for the accommodation. The other two major problems at the intersection are rear-end and angle collisions. In order to diminish the quantity of these types of crashes, adjustment of the amber phase of the signal timing is needed to provide drivers with enough time to cross the intersection. Furthermore, additional speed limit signs


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would be added to any missing in northbound of Linwood Street and eastbound of Davidson Street West. The above recommendations are only for the intersection of Davidson Street West and Linwood Street. With the overall view of the intersection through dissecting the condition diagrams and collision diagrams, the analyst can determine tactical countermeasures to decrease the potential hazards on the roadway and increase the safety for the drivers.


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INTRODUCTION This report summarizes the results from the collision data analysis performed for the intersection of Davidson Street West and Linwood Street in Wayne County, Michigan. The drawings for condition diagrams for existing and with improvements, 2010 and 2011 collision diagrams are included in the Appendix of the report. The report is distributed into the following sections:

Introduction

Site Description

Data Collection

Data Analysis

Suggested Countermeasures

Conclusions and Recommendations

This project has been designed to determine the probable causes and countermeasures of collisions at a subject intersection in Michigan. The purpose of this study is to develop strategic planning from the analysis of the collision data and traffic information to reduce the amount of collisions happening at the site. The study intersection is situated at Davidson West Street & Linwood Street. The objective for such location due to the high collision volumes in the past few years. This intersection for the study, shown in the map below in Figure 1, is located near the John C Lodge Freeway and Davidson Freeway.

FIGURE 1 - Map of Study Location


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SITE DESCRIPTION For this intersection study, Davidson West Street is the eastbound/westbound primary roadway and Linwood Street is the northbound/southbound roadway. Both roadways are undivided and contained exclusive left-turn lanes. The photo of the study intersection in plan view is shown in the following Figure 2. As shown in the photo, Mobil gas station is located at northwest corner and McDonald’s restaurant is positioned at the northeast corner. On the south side, KFC restaurant is situated at southwest corner and Future Fuel Station is sited at southeast corner. These establishments and the surrounding businesses along Davidson Street West created many access points which attract a lot of traveling vehicles to those locations. Those inadequate locations of driveways cause some concerns for possible collisions.

FIGURE 2 - Plan View (Intersection of Davidson St. W. & Linwood St.

The streetview photos for both directions of Linwood Street and Davidson Street West are shown in the following Figures 3 to 6.


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FIGURE 3 - Northbound of Linwood St.

FIGURE 4 - Southbound of Linwood St.

FIGURE 5 - Eastbound of Davidson St. W.

FIGURE 6 - Westbound of Davidson St. W.

To provide a complete and visual view of the many traffic components contained at this intersection, a detailed condition diagram has been established and available in the Appendix. The diagram includes the general geometry and location of traffic signs and signals along the roadways. It should be noted that the existing P.M. peak hour signal timing plan is also included to provide easy access for the analyst for future modifications. DATA COLLECTION In order to conduct the safety improvement analysis at the subject intersection, a data collection process was performed. A detailed search of traffic volume data was conducted from the SEMCOG.org database. From the database, the most recent volumes that were available was from 2009. For the purpose of projecting to the current 2013 volumes, a 0.5% growth rate was used. This growth rate was assumed based on the consideration that the growth rate in this struggling area is likely negative and 0.5% represents a conservative assumption. With the adjusted volumes, the total movements only have a slight increase from 2009. The results of 2009 traffic volumes and the estimated volumes for 2013 are


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shown in the following Table 1. In addition to the table, a visual perspective of the turning movements at the intersection is presented in Figures 7 and 8 to display the results.

2009 Estimated 2013

Peak Hour

RT Thru LT RT Thru LT Total

Movements RT Thru LT RT Thru LT

Total Movements

Davidson St. W.

AM 120 1620 120 50 1175 95 3180 122 1653 122 51 1199 97 3244

PM 130 1580 115 90 1690 90 3695 133 1612 117 92 1724 92 3769

Linwood St.

AM 75 255 100 75 330 145 980 77 260 102 77 337 148 1000 PM 65 295 120 135 275 80 970 66 301 122 138 281 82 990

TABLE 1 - Peak Hour Traffic Volumes for 2009 & Estimated 2013

Traffic crash data was gathered from SEMCOG.org for the three years (2009 to 2011) for analysis. Each crash report was reviewed and verified with the police officer’s original assumption to determine if any difference in the crash type. Once this step was completed, the crash reports would be used to build a collision database with the appropriate headings that would be useful for traffic analysts to perform searches of crash details. A summary of the collision database can be found in the Appendix of the report. With the construction of the collision database, the analyst could use the data to produce a graphical representation, such as a collision diagram of the crash locations at the intersection each year. The collision diagrams for the study intersection in 2010 and 2011 are available in the Appendix of this report.

A spot speed study on Davidson Street West was performed during A.M. off peak period to observe the speed distribution. The street has a speed limit of 35 mph and a sample of 100 vehicles were counted for the study. The two concerns of speed distribution in a spot speedy study is the 50th and 85th percentiles. The 50th percentile represents the mean speed of the study and the 85th percentile represents the 85% of vehicles are traveling during the observed period. Due to the high volume of traffic, a video camera was used to record the observed period and then analyze the results on the computer. A measure of each vehicle traveling from point A to point B for certain amount of time was calculated to conclude on the speed. From the results of the study, it was determined that 50th

FIGURE 7 - A.M. Peak Hour Traffic Volumes in 2013

FIGURE 8 - P.M. Peak Hour Traffic Volumes in 2013


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percentile of distribution falls at 35 mph and 85th percentile between 37 and 39 mph. Using a 5 mph limit as a deviation from the posted speed limit, the 85th percentile of speed did not exceed the limit. Therefore, the posted speed limit would not need adjustment. Table 2 below is the summary of the spot speed study.

Speed (mph)

Frequency of Vehicles

Cumulative Frequency

Cumulative Percentage (%)

Speed Percentile

25 3 3 3

27 4 7 7

30 4 11 11 32 19 30 30

35 20 50 50 50th

37 23 73 73 85th

39 15 88 88

41 10 98 98

44 2 100 100

TABLE 2- Spot Speed Study Table

Traffic signal timing information for the intersection was obtained through the MDOT website. The characteristics of the signal timing in each phase and interval time are displayed in the following Table 3.

From the condition diagram, the analyst can generate databases to provide geometry, signs and traffic signals of the intersection. Tables 4 and 5 are the databases for the traffic signal and geometry of the study intersection.

Main Street

From To Class Dir./Lanes Lane

Width (ft)

Pavement Type

Shoulder

Terrain Alignment Road

Condition Type Width

(in.)

Davidson St. W.

Dexter Ave.

14th St.

Arterial EB/3, WB/3

12 Asphalt Paved Curb

6 Level Straight Fair

TABLE 5 - Roadway Database

Signal Timing

Cycle Length

(s)

No. of Phases

Lead/ Lag

Phase/Interval Length

NB SB EB WB

Thru Left Thru Left Thru Left Thru Left G A G A G A G A G A G A G A G A

90 4 Lead 28 5 9 5 28 5 9 5 43 5 9 5 43 5 9 5

TABLE 3 - Traffic Signal Timing Database

TABLE 3 - Traffic Signal Timing Database

Main Street

Cross Street

Type of Support

No. of Signal Heads

Controller Ped.

Signal Ped. Signal

Std/Non-Std Main Street

Cross Street

Type Std/Non-Std

Davidson St. W.

Linwood St.

Span Wire

3 3 Fixed Std Yes Std

TABLE 4 - Traffic Signal Database

TABLE 4 - Traffic Signal Database


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DATA ANALYSIS

With the available data collected for this collision study, the analyst can now create tables and charts to

describe the findings through the collision analysis. This intersection experienced a total of 90 crashes

in a three year study period with an annual average of 30 crashes. For a two year study period, the total

crashes was 61 with annual average still remained at 30 crashes. From reviewing the collision diagrams,

which were prepared and are available for the intersection in the Appendix of this report, several trends

were noticed in the collision history of this intersection.

First, there have been many left-turn head-on collisions occurred turning into driveways from opposing direction. Many of these collisions happened due to drivers distracted by the establishments at the intersection and carelessly violating traffic rules. It could be asserted that after the improvements around this intersection that perhaps these collisions may decrease. Further, the majority of collisions at this intersection were of the rear-end related. While these crashes are relatively minor in nature, they do need to be addressed in the new design of this parcel. One way in which this will be addressed is through the improvement of the clearance intervals for this signal, with proper clearance intervals tending to reduce this inordinate number of rear-end crashes. Another issue that was prominent at this intersection was the angle collisons that were seen during this three year period. The majority of these were due to violating the signal timing. It is recommended to adjust the signal timings on Davidson Street West to allievate this safety issue. It is worth noting that despite the high number of angle crashes no fatalities or A-level angle crashes occurred in the analysis period as this intersection. Figure 9 is the summary of crash types in the three years of analysis and Figure 10 is the summary of the collision by time periods.

FIGURE 9 - Bar Chart of Crash by Type (2009 to 2011)


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FIGURE 10 - Bar Chart of Time of Crash (2009 to 2011)

SUGGESTED COUNTERMEASURES From the precise analysis of the data using condition diagram and collision diagrams, the analyst can predict some probable causes of the collisions. For an easier description for a better understanding, an accident pattern table, as shown in Table 6 was developed. Throughout the table, there are lists of the collision types, causes and countermeasures that occur at this intersection.

Accident Pattern Probable Cause General Countermeasure

Right-angle collision at signalized intersection

Inadequate signal timing Adjust amber phase

Provide all-red clearance phases

Add multi-dial controller

Retime signals

Rear-end collision at signalized intersection

Inadequate signal timing Adjust amber phase

Provide progression through a set of signalized intersections

Pedestrian crossings Install/improve signing or marking of pedestrian crosswalk

Slippery surface Overlay pavement

Provide adequate drainage

Reduce speed limit on approaches

Collisions between vehicles traveling in same direction

Roadway design inadequate for traffic conditions

Remove parking

Reduce speed limit.


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Accident Pattern Probable Cause General Countermeasure Collisions at driveways Left-turning vehicles Install median divider

Improperly located driveways Regulate minimum spacing of driveways

Regulate minimum corner clearance

Move driveway to side streets

Install curbing to define driveway location

Consolidate adjacent driveways

TABLE 6 - Accident Pattern Table

From the general countermeasure suggested, the analyst could decide on the more precise solutions for the study intersection. A modified collision diagram for the improvements of the intersection can be found in the Appendix. With the modifications of the intersection, the results from the countermeasures could be effective. By providing additional speed limit signs, the drivers would be cautious about speeding along the roadway. Moreover, additions of raises median islands on all four legs would prevent any access by vehicles to attempt making left-turn movements into driveways of opposing stores. Also, adjusting the signal timings of Davidson Street West would provide drivers additional time to react to the intersection and reduce the number of rear-end collisions. The reduction of lane width from the original 12’ to 11’ could alert drivers to be aware of the surrounding vehicles. Finally with the new pavement markings, the drivers would be able to maintain at the appropriate lane without confusion. CONCLUSIONS & RECOMMENDATIONS As a result of this analysis, it is shown the importance of collecting and analysing of collision data to determine causes and solutions to reduce collisions on the roadways and intersections. Crash data in the period of 2009 to 2011 were used to identify vehicle, enivronmental and driver related factors that were significant in the causes of the crashes. The focus on establishing the origins of the causes of the major collision types was a key component in the study. With the major collision affecting the intersection is identified, a list of countermeasures could be developed. The list below is the summary of the countermeasures:

Install speed limit signs on northbound of Linwood and eastbound of Davidson West

Install raised median islands on north, south, east and west legs of the intersection

Optimize signal timings for both eastbound and westbound of Davidson West to adjust amber

phase

Modify pavement markings as shown in collision diagram

Reduce lane width from 12 ft. to 11 ft. for all four directions to adjust with the median additions


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The analysis suggested that there are no tremendous increase in any type of crashes in the three year period. However, it does not mean the crashes of any type has decreased. The recommended countermeasures to enhance the existing intersection should lessen the probability of continued trend of the crashes. Even with the proposed improvements to the roadways, drivers should be always driven with utmost care while traveling on the roads, as well as changing lanes and making directional turns.


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REFERENCES SEMCOG. Detroit Southeast Michigan Council of Government. http://www.semcog.org MDOT. Michigan Department of Transportation. http://www.michigan.gov/mdot/

safety assessment of the intersection of davidson st and linwood st shun cheung

Documents

past traffic volumes

peak hour traffic volumes

table of tables table

study of crash analysis

data analysis

crash analysis project

traffic activities

traffic signal database