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CSAH 30 and Braddock Trail – Intersection Assessment

Review by: Kevin Collins, Senior Traffic Technician, Dakota County and Kristi Sebastian, PE, PTOE ,

Dakota County Traffic Engineer

Evaluation Conducted Fall 2015 – March 2016

Improvement recommendations for the County CIP summary – July 2016

Reason for Study: The original concern at this intersection in the summer of 2015 was related to signing

and marking inconsistency on the northbound approach. Old pavement markings that were previously

covered over became visible again, creating an unintended lane assignment for the northbound

approach. This issue was resolved in August of 2015 with the removal of the through arrow in the right

most lanes and moving it to the left most lane to go northbound. The change addressed the left turn

type collisions occurring at the intersection.

In addition to addressing this issue, other concerns were raised regarding pedestrians and side road

traffic operation including the request for adding left turn arrows. Traffic staff assessed the intersection

regarding concerns for overall operation, pedestrian safety and operation for the traffic along Braddock

Trail turning onto or crossing CSAH 30.

Existing Traffic Control and Geometrics: The intersection of CSAH 30 and Braddock Trail is a signalized

intersection. The signal was installed in 1993. Eagan High School and Dakota Middle School are located

on the northwest side of the intersection with access to the schools from Braddock Trail. This creates

heavy turn movements and side road crossing movements in the morning when school is in session.

CSAH 30 is a four lane divided roadway with separate left turn lanes. The roadway narrows to one lane

in each direction with center left turn lanes east of Braddock Trail.

Braddock Trail was modified and signal revisions were made in 2012. This was done to align with

changes along Braddock Trail and to address the high eastbound left and southbound left turning

movements in the morning. The side road approaches have shared left/through lanes and separate

right turn lanes (See Appendix A -Existing Geometry). The approaches need to have the same lane

configuration to meet driver expectation and ensure safe operation. Therefore, to provide an exclusive

turn lane for southbound right turns to meet the high traffic volumes, the other lane must be a shared

left and through lane in both directions to provide a consistent message to drivers. If the northbound

lane were an exclusive left turn lane while the southbound lane remained a shared left/through lane,

northbound drivers would not expect through traffic to be approaching from the nearest lane.

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Traffic Volumes: A turning movement count was completed in May 2014; see Figure 1 below for AM

(7:00-8:00 a.m.) and PM (5:00-6:00 p.m.) peak hour volumes. While traffic is higher along CSAH 30 in

the afternoon, the turning movements from CSAH 30 to the north on Braddock Trail as well as the side

road traffic on Braddock Trail is highest in the morning when school is in session. The following graph

summarizes the morning turning movement volumes at the intersection:

Traffic Volume Figure 1: AM and PM peak hours – May 13, 2014

Crash Data: To evaluate safety at the intersection, a three year evaluation was conducted. This is the

typical evaluation period to assess trends and identify any potential issues as well as to provide standard

comparisons with other similar locations. The 2015 collision data was not available from the state. In

addition to evaluating recorded crash data, County staff discussed the intersection and safety concerns

with City engineering and law enforcement staff.

The crash rate at this intersection is 0.61crashes per million entering vehicles. This rate is lower than the

state crash rate of 0.69 for similar intersections. The severity rate for this intersection is 0.89. The

severity rate is also lower than the state severity rate of 0.96 for similar intersections. The majority of

collisions at this location were rear end and right angle crashes (77%). The majority of the rear end

crashes happened in the morning hours; right angle crashes occurred in the evening.

2011 to 2014 Crash Data (see attached collision diagram):

Year Right Angle Rear End Left Turn Sideswipe Total

2011 1 1 2

2012 2 2 4

2013 2 1 1 4

2014 1 1 1 3

Total 4 6 2 1 13

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Traffic Operations: Eagan High School and Dakota Hills Middle School are located just north of this

intersection. There is relatively low traffic along Braddock Trail from the neighborhood to the south,

except for the 6:30 a.m. to 8:00 a.m. time frame when school is in session. On school days, traffic

activity is higher for pedestrians, bicycles and motor vehicle in all directions during the morning

compared to other times of the year or other hours of the day. Likewise, traffic is also higher along

CSAH 30 at this time of day as motorists are traveling to work or to the school.

The existing traffic signal has timing plans in place to best address the traffic conditions during this time

of day. Traffic on Braddock Trail operates with permissive phasing; this means that left turn traffic must

yield to through traffic before proceeding. A signal revision in 2012 added a southbound right turn

green arrow that is concurrent with the eastbound left turn movement in order to reduce delay for this

heavy southbound right turn movement. The eastbound left turn is also a heavy move and requires a

large portion of the green time. Even with the large amount of time allocated, on occasion during the

morning peak hour while school is in session, eastbound left turning traffic can extend past the turn

lane into the through lane for eastbound CSAH 30.

Pedestrians are accommodated through cross walks throughout the intersection with pedestrian push

buttons to activate the pedestrian signal indications. With the 2012 signal revisions described above,

count down timers were added to provide pedestrians with information regarding when the time to

cross would be ending. This provides clarity for the pedestrians and bicyclists, including students

crossing in this area.

Left turn signal phasing, including left turn arrows to allow left turns to turn on an exclusive phase and

flashing yellow arrows to allow left turns after yielding to opposing traffic during lighter traffic times,

requires designated left turn lanes. The current configuration along Braddock Trail would need to be

modified to accommodate separate left turn lanes (See Appendix B – Proposed Geometry).

Field Observations: The primary focus of the citizen’s concern at the intersection related to the

northbound approach. The traffic observations reviewed these northbound operations.

Traffic observations were conducted by reviewing the video. They are summarized as follows:

• 6:30 a.m. to 8:00 a.m., October 28, 2015

o Weather Conditions were rainy.

o Volume was high.

o At several different times the left turn lane would have a long queue; however, most

times it cleared.

o There were several cars that would use the right turn lane as a thru lane when two or

more cars would queue up to make a left turn. It was noticed that once one car made

the maneuver several more cars would follow.

o There were a high number of left turns observed.

• 6:30 a.m. to 8:00 a.m., October 29, 2015

o Weather Conditions were rainy.

o Volume was high.

o There were long queues but all cleared.

o No motorists used the right turn lane as a through lane.

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o Northbound left turns were minimal during this time frame; this allowed the majority of

cars to make the through movement (to cross CSAH 30) with minimal delay or difficulty.

• 4:30 p.m. to 5:30 p.m., October 29, 2015

o Weather Conditions were overcast.

o Volumes were low.

o All cars used proper lanes to turn from Braddock Trail .

• 6:30 a.m. to 8:00 a.m., October 20, 2015

o Weather Conditions were overcast.

o Volume was high.

o There were long queues but all cleared.

o No motorists used the right turn lane as a thru lane.

o Northbound left turns were minimal during this time frame; this allowed the majority of

cars to make the through movement (cross CSAH 30) with minimal delay or difficulty.

o One motorist attempted to use the right turn lane as a through lane. At the same time,

two left turning cars cleared allowing the traffic waiting to cross CSAH 30 to proceed.

This resulted in the motorists which crossed improperly in the right lane needing to yield

to the traffic on his left before he could continue in the thru lane past the intersection.

Overall Field Review Summary: The operation worked very well throughout the day with no delay

except for the morning rush hour conditions for school days. During the morning rush hour, when traffic

volumes were high, northbound and southbound traffic would form longer queues which would

typically clear in the same cycle. The northbound traffic would typically navigate properly in conjunction

with left turners in order to proceed through the intersection. There were some occurrences observed

where traffic would use the right turn lane to pass left turning traffic, but this was not typical.

Capacity Evaluation: A signal analysis was conducted to determine traffic flow operation with existing

side road configuration on Braddock Trail and a proposed configuration of separate left, through and

right turn lanes southbound and a separate left plus a shared through/right turn lane northbound. With

the proposed configuration, left turn arrows to allow protected or permissive turns were assessed.

The high volume of traffic on CSAH 30 and heavy eastbound left turn movement in the morning rush

hour do not provide flexibility in giving any additional traffic signal time for Braddock Trail. Providing

exclusive left turns along Braddock Trail requires lane changes including a new southbound right turn

lane to provide a left turn only lane southbound. The northbound traffic could then be configured with

a left turn lane and shared through/right lane. While this configuration provides a better lane balance

based on traffic volumes, the left turn and through traffic would still be using the green time provided

for Braddock Trail today (no additional time can be used due to the heavy CSAH 30 volumes). The

following chart summarizes the level of service and delay. Level of service ranges from A (no delay) to F

(severe delay).

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Capacity Operation Summary:

Condition West

Approach

(EB)

East

Approach

(WB)

South

Approach

(NB)

North

Approach

(SB)

Overall

Existing Configuration - AM C (26.9 sec) C (32.4 sec) C (30.6) B (14.0) C (24.5)

Proposed Geometry – AM C (29.2 sec) C (34.9 sec) D (42.6) B (13.7) C (26.8)

Existing Configuration - PM B (12.8) C (21.6) C (21.0) B (12.6) B (15.8)

Proposed Geometry – PM B (13.6) C (21.8) C (22.3) B (10.5) B (15.9)

Level of Service (average delay per vehicle in seconds)

The simulation showed that adding the southbound right turn lane and exclusive left turns would result

in similar level of service compared to the existing condition. The higher level of service for the

southbound traffic reflects that the heavy right turn movement is receiving a green arrow concurrent

with eastbound traffic. While the south approach shows a slight increase in delay, in actual operation,

the efficiency of separating the left turns will provide an overall benefit. While the level of service or

delay would not improve, the new lane alignment would provide for better lane balance and a better

alignment of traffic northbound across CSAH 30. As traffic increases, it is expected that during the

largest peak in the AM, traffic may not clear the side road in one signal cycle.

Intersection Improvement Considerations:

Based on assessment of safety and operation, extending the eastbound left turn lane to reduce the

potential for high speed read end collisions due to traffic extending past the turn lane is a strong

consideration.

Changes to the intersection to provide northbound and southbound exclusive left turn lanes and the

appropriate left turn phasing is the best long term configuration. This change would require left turn

lanes on Braddock Trail in each direction. Due to the high volume of right turns from the high school, a

new right turn lane for southbound traffic would need to be constructed to create a separate

southbound through lane. While such improvements would provide clear times for left turning traffic

and would allow shared northbound through/right turn traffic to use the right most lane, overall the

intersection operation would only marginally improve during the morning peak time. The safety and

operation review does not indicate an immediate need for change. Provided the traffic volumes stay

consistent along Braddock Trail and no safety issues arise, planning for this modification as a long-term

change when the signal is replaced in approximately the next five to ten years would be applicable.

Recommendation Summary: The following is recommended for improvements.

1. Short Term (2017 CIP) – extend the eastbound left turn lane to provide additional storage for

traffic. Currently, this high volume movement during the morning, when school is in session,

can extend into the through lane. This project to create additional storage will reduce the

potential of rear-end collisions along this high speed roadway.

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2. Longer Term – Side road modifications to create a southbound exclusive lane and new left turn

operation for Braddock Trail. While the change will not specifically improve delay, it will create

a more standard approach for side road turning and crossing movements which could be

helpful, particularly in the morning when school is in session. The signal was installed in 1993.

Based on review of the signal system and extent of this project work, completing these

modifications with the signal replacement would be the most efficient and cost effective

approach. Timing of a potential project also needs to be considered along with other safety and

operational needs of the city and county for resources.

Project would include:

• Add an exclusive southbound right turn lane.

• Reconfigure Braddock Trail to have a separate southbound right, through and left turn

lanes.

• Change pavement markings and signing for the northbound approach to have a separate

left turn and shared through/ right turn lane.

• The improvement would require the City to work with ISD 196 regarding right of way.

• The project would entail the geometric changes to the right turn lane and relocation of the

northwest pole to accommodate the new lane.

• Signal revision to include protective or permissive left turns on Braddock Trail would also be

part of the project scope to provide for flexibility with timing, consistent lane designations

for the side road to best meet driver expectation long term and provide for a better lane

balance based on traffic turns.

• Upgrade signal to ADA standards for pedestrian safety and mobility.