Dern Spring Creek Preliminary Traffic Engineering Report Addendum · 2017-10-02 · Dern / Spring...

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Preliminary Traffic Engineering Report

ADDENDUM DERN / SPRING RECONSTRUCT

HSIP 1-2(192)118 UPN: 8626000

October 25, 2016

Prepared by:

ROBERT PECCIA & ASSOCIATES Helena, MT

Scott Randall, PE, PTOE

PRELIMINARY TRAFFIC ENGINEERING REPORT ADDENDUM DERN / SPRING RECONSTRUCT HSIP 1-2(192)118 UPN: 8626000

Prepared For:

MONTANA DEPARTMENT OF TRANSPORTATION Consultant Design Bureau Helena, Montana

Prepared By:

ROBERT PECCIA & ASSOCIATES 825 Custer Avenue Helena, Montana 59604 (406) 447-5000 www.rpa-hln.com

October 25, 2016

Dern / Spring Reconstruct HSIP 1-2(192)118 Preliminary Traffic Engineering Report (Addendum) UPN: 8626000

Robert Peccia & Associates October 24, 2016 i

TABLE OF CONTENTS Table of Contents ....................................................................................................... i

List of Figures ....................................................................................................................................... i List of Tables ........................................................................................................................................ i

1. Introduction ......................................................................................................... 1

2. Options Advanced ............................................................................................... 1

3. Additional Evaluation of Options ........................................................................ 4 3.1. Public Involvement ....................................................................................................................... 5

4. Additional Considerations ................................................................................... 8 4.1. Vehicle Speeds ............................................................................................................................ 8 4.2. Safety ........................................................................................................................................... 8

5. Conclusion and Recommendations .................................................................... 9

Appendix A: Informational Meeting Sign-in Sheets Appendix B: Public Comments

LIST OF FIGURES Figure 1: Option 7.B. Conceptual Design ............................................................................................... 2 Figure 2: Option 8.A. Conceptual Design ............................................................................................... 3 Figure 3: Traffic Signal Conceptual Renderings ..................................................................................... 6 Figure 4: Single-lane Roundabout Conceptual Renderings ................................................................... 7 Figure 5: Recommended Conceptual Configuration ............................................................................... 9

LIST OF TABLES Table 1: Revised Traffic Operational Analysis ........................................................................................ 4 Table 2: Preliminary Cost Estimates ....................................................................................................... 4


Robert Peccia & Associates October 24, 2016 1

1. INTRODUCTION This report serves as an addendum to the Preliminary Traffic Engineering Report1 (Traffic Report) dated December 18, 2015. The Traffic Report identified and evaluated 12 potential improvement options for the intersection of US Highway 2 (US 2) and Dern/W Springcreek Roads. The goal of the improvement options is to improve safety and operational concerns by providing appropriate traffic control and geometrics.

Of the 12 potential improvement options, 4 were found to best address traffic and safety issues and concerns identified in the report. Those options that met the identified safety and operational needs, and that were seen to be implementable, were advanced for further consideration. The four advanced options include the following:

Option 4.B. Close Dern Approach – With Left-turn Lane Option 7.B. Traffic Signal – With Left-turn Lanes Option 8.A. Single-lane Roundabout – Four-legged Roundabout Option 8.B. Single-lane Roundabout – Three-legged Roundabout

A meeting was held on January 14, 2016 with MDT staff to discuss the four advanced options and to determine if enough information was available to select one as the preferred option. At the meeting, it was decided that the traffic signal and four-legged roundabout options (Options 7.B. and 8.A.) should be presented to the public at an informational meeting. It was also decided that detailed traffic simulations and 3D renderings should be developed to aid in the public outreach effort. The following sections discusses the advanced options in more detail and outlines the steps conducted to determine the preferred option.

2. OPTIONS ADVANCED The options advanced in the Traffic Report all improve safety and operations to varying degrees. Each option also has implementation challenges related to constructability, impacts, right-of-way needs, and cost. The following provides a summary of each option and discusses the ultimate determination as decided at the January 14th meeting. More information for each option is contained in the Traffic Report.

OPTION 4.B. CLOSE DERN APPROACH – WITH LEFT-TURN LANE This option would result in the closure of the Dern Road approach south of US 2 and the construction of an eastbound left-turn lane. Closing the Dern Road approach would address the right-angle crash trend associated with vehicles crossing US 2 from Dern Road. In addition, the closure of the Dern Road approach would allow for improved geometric reconstruction of the US 2 mainline and W Springcreek Road. The addition of an eastbound left-turn lane would help address the rear-end crash trend resulting from eastbound vehicles turning left onto W Springcreek Road. The existing traffic control (stop control on W Springcreek Road) would remain under this option. This option does not fully address operational concerns at the intersection and results in failing LOS during the peak hours.

Discussion of this option at the meeting focused on acceptance from the local land owners and Flathead County Commission. In the past, the Commission indicated reluctance to close Dern Road due to anticipated public pushback and liability. In order for the approach to be closed, property owners served by the approach would have to initiate the request to close the approach. Closing the approach may also

1 Preliminary Traffic Engineering Report, Dern / Spring Reconstruct, Robert Peccia and Associates, December 18, 2015



hinder emergency vehicle response. Ultimately, it was decided to drop this option from further consideration due to lack of local support.

OPTION 7.B. TRAFFIC SIGNAL – WITH LEFT-TURN LANES Option 7.B includes installation of a traffic signal and construction of eastbound and westbound left-turn lanes. Multiple traffic signal warrants are currently met at this location. Reevaluation of the warrants would be necessary after the full US 93 bypass is constructed to determine if they are still met. The traffic signal would help improve traffic operations and reduce vehicle delay. The configuration is shown to accommodate existing and projected traffic demands. Through discussion of this option at the meeting, it was decided that the option should be further refined and presented to the public. There are some safety concerns with the installation of a traffic signal, particularly on a high-speed highway. Some safety benefits may be realized through improved sight distances, geometrics, and the inclusion of dedicated turn lanes. However, new crash trends may be introduced with a traffic signal.

Following the meeting, the configuration of this option was modified to further improve geometrics. The modified layout is shown in Figure 1. To aid in the public outreach effort, traffic simulations and 3D renderings were developed for this option using the modified configuration and updated traffic analysis. More information about this option and the public outreach effort is contained in Section 3.

FIGURE 1: OPTION 7.B. CONCEPTUAL DESIGN



OPTION 8.A. SINGLE-LANE ROUNDABOUT – FOUR-LEGGED ROUNDABOUT This option includes construction of a single-lane roundabout near the existing intersection. This option would address safety issues identified at this intersection and would improve traffic operations. A roundabout would reduce the number of vehicle conflict points and would reduce vehicle speeds through forced deflection. Operationally, a single-lane roundabout is shown to accommodate existing and projected peak hour demands. Figure 2 shows the conceptual design configuration.

During the meeting, this option was identified as the likely preferred configuration for the intersection. The option provides the greatest benefits to safety and addresses operational concerns. This configuration would require the most right-of-way and results in substantial construction impacts, however. It was decided that this option would be further refined and presented to the public. Section 3 discusses this option in more detail.

FIGURE 2: OPTION 8.A. CONCEPTUAL DESIGN

OPTION 8.B. SINGLE-LANE ROUNDABOUT – THREE-LEGGED ROUNDABOUT This option includes the construction of a three-legged roundabout west of the existing intersection. The roundabout would include realignment of the W Springcreek Road approach. The Dern Road approach would remain as a stop-controlled intersection just east of the roundabout. The intent of this option was to shift the roundabout further to the west to try to improve geometrics and grades on the W Springcreek Road and Dern Road approaches. Preliminary designs showed that this option would not improve geometrics or



grades compared to Option 8.A. Concern was also expressed during the meeting about introducing operational and safety issues associated with vehicles turning left from Dern Road. It was decided to drop this option from further consideration due to poor alignment and operational concerns.

3. ADDITIONAL EVALUATION OF OPTIONS Options 7.B and 8.A were identified as the most reasonable options to address the concerns with the intersection. Further refinement to the preliminary design, estimated costs, and traffic operational analysis from the Traffic Report were made following the meeting. The updated traffic operational analysis is shown in Table 1.

TABLE 1: REVISED TRAFFIC OPERATIONAL ANALYSIS

Leg

Existing Conditions (2015) Projected Conditions (2037)

AM Peak PM Peak AM Peak PM Peak

Delay (s) LOS Delay (s) LOS Delay (s) LOS Delay (S) LOS

Option 7.B (Traffic Signal) 15.7 B 14.7 B 18.1 B 17.2 B

Northbound 18.2 B 20.2 C 21.5 C 24.4 C

Southbound 20.2 C 22.1 C 25.9 C 28.7 C

Eastbound 16.3 B 11.2 B 19.6 B 10.6 B

Westbound 11.8 B 15.1 B 10.8 B 18.5 B

Option 8.A (Roundabout) 8.3 A 8.1 A 16.4 C 14.4 B

Northbound 5.6 A 4.1 A 7.7 A 4.8 A

Southbound 4.8 A 6.0 A 6.0 A 8.4 A

Eastbound 10.3 B 6.2 A 22.9 C 8.2 A

Westbound 5.9 A 9.6 A 7.6 A 18.8 C

Revised estimated construction costs were also developed for the two options. The costs include construction, right-of-way, and utility relocation estimates. Table 2 shows the preliminary cost estimates for two improvement options.

TABLE 2: PRELIMINARY COST ESTIMATES

Preliminary Cost Estimates

Improvement Option

7.B (Traffic Signal) 8.A (Roundabout)

Construction(i) $2,807,000 $4,331,000

Right-of-way(ii) $349,000 $464,000

Utility Relocation(iii) $334,000 $334,000

TOTAL $3,490,000 $5,139,000

(i) Construction estimates do not include IDC or inflation. Contingency 30%, Mobilization 10%, CE 10%.

(ii) R/W estimates based on discussions with local realtors and listings for undeveloped subdivided tracts of similar size in the project area.

(iii) Utility relocation estimates includes 30% contingency. Unit cost estimates per preliminary discussion with MDT Utilities section.



3.1. PUBLIC INVOLVEMENT The traffic signal and four-legged roundabout options were presented to the public at an informational meeting on September 13, 2016. The meeting was conducted as an open house from 5:00 PM to 6:30 PM followed by a presentation. There were 22 people who signed the attendance sheet at the meeting (see Appendix A). In advance of the meeting, an informational flyer was developed and distributed to adjacent landowners. The meeting was also advertised in the local newspaper and press releases were distributed to area media outlets. Traffic simulations and 3D renderings were developed to aid in presenting the options to the public. Samples of the renderings are shown in Figures 3 and 4.

Written and verbal comments were received at the meeting and during the public comment period. During the meeting, there was general support for either the traffic signal or roundabout configurations. Some were more in favor of a roundabout, while others felt the traffic signal was a better alternative. In general, there was consensus that improvements to the intersection were needed. Comments were also made regarding non-motorized use and connectivity.

A discussion was held during the meeting regarding the speed limit of the highway. Some comments were made expressing a desire to reduce the speed limit to 45 mph. MDT noted that simply changing the speed limit alone will likely not reduce vehicle speeds. Reduction in speed limits should be combined with additional efforts to change driver behavior.

A total of 22 written comments were submitted regarding the intersection project (see Appendix B). As with the verbal comments made during the informational meeting, there were comments both supporting and against the roundabout and traffic signal configurations. There was also a desire for a reduced speed limit along the highway expressed in some written comments.



FIGURE 3: TRAFFIC SIGNAL CONCEPTUAL RENDERINGS

Northbound

Southbound

Eastbound

Westbound



FIGURE 4: SINGLE-LANE ROUNDABOUT CONCEPTUAL RENDERINGS

Northbound

Southbound

Eastbound

Westbound



4. ADDITIONAL CONSIDERATIONS

4.1. VEHICLE SPEEDS The speed limit of the highway is currently posted at 60 mph. A desire was expressed by the public during the informational meeting and through written comments to reduce the speed limit to 45 mph. It was discussed during the informational meeting that changing the speed limit alone will likely not result in reduced speeds. Additional measures are needed to effectively reduce vehicle speeds.

Vehicle speed data was collected as part of the data collection effort for the Traffic Report. The speed data showed that 85th percentile speeds at the intersection are slightly below the posted speed limit of 60 mph (59.1 mph eastbound, 57.4 mph westbound).

MDT conducted a speed study dated October 27, 2015 for US 2 between Hartt Hill Drive and West Valley Drive. The speed study was conducted in response to a request from the Flathead County Board of Commissioners. The request was made to specifically evaluate if the existing 45 mph speed zone should be extended west to West Valley Drive. The speed limit transitions from 45 mph to 60 mph in the westbound direction at Hart Hill Drive.

In the study, vehicle travel speeds were sampled in both directions at nine locations. The results of the study showed that the majority of the traffic stream was traveling at speeds in excess of 45 mph throughout the study area. The speed study concluded that, “invoking a restrictive 45 mph speed limit would not provide the desired speed reduction as it is too far below the desired travel speeds for realistic operation”. The recommendation of the speed study was to make no changes to the existing posted speed limits. The County Commission verbally concurred with the results of the speed study at the January 14, 2016 meeting.

4.2. SAFETY A detailed discussion about safety is included in Section 4.0 of the Traffic Report. The crash data shows trends of right angle and rear-end crashes. The identified crash trends may be addressed to varying degrees through the identified improvement options. Roundabouts in particular have shown to result in significant reductions in injury and fatal crashes over stop-controlled or signalized intersections. Roundabouts have the safety benefit of reduced conflict points which decreases opportunities for crashes. In addition, roundabouts result in reduced vehicle speeds through physical deflection measures. Studies of intersections converted from traffic signals or stop-control to roundabouts within the United States have shown a reduction in injury crashes of 72 to 80 percent and a reduction in all crashes of 35 to 47 percent.

Construction of a roundabout is likely to result in the greatest speed reduction through the intersection. Roundabouts force vehicle deflection which results in lower speeds. The lower vehicle speeds created by roundabouts is a significant contributor to the reduction in severe crashes. Installation of a traffic signal may address some existing crash trends at the intersection. However, new crash trends may develop as a result of the traffic signal. In addition, a traffic signal is unlikely to have the same benefit of lowering vehicle speeds as a roundabout.



5. CONCLUSION AND RECOMMENDATIONS The Traffic Report identified 12 improvement options for the intersection of US 2 and Dern/W Springcreek Roads. The improvement options were evaluated to assess how issues and concerns related to safety, operations, and construction feasibility would be addressed. Geometric improvements to the intersection and to the US 2 mainline are needed to address identified crash trends. A higher form of traffic control, such as a traffic signal or roundabout, is also needed to address capacity issues and other identified crash trends.

Two of the twelve improvement options were identified to best address operational and safety concerns while likely being implementable and feasible to construct. The two options (Option 7.B. Traffic Signal with Left-turn Lanes and Option 8.A Single-lane Four-legged Roundabout) were further refined from the Traffic Report and were presented to the public at an informational meeting on September 13, 2016. Comments from the public at the meeting and during the public comment period expressed a desire for improvements to the intersection. Some comments were in support of a roundabout, while others preferred a traffic signal. There was not an overwhelming preference for either option.

Based on the evaluation in the Traffic Report, subsequent refinement of options, and comments from the public, it is recommended that a single-lane, four-legged roundabout (Option 8.A) be constructed at the intersection of US 2 and Dern/W Springcreek Roads. The recommendation is made due to the operational and safety benefits of the configuration. A roundabout provides the greatest benefit to safety and provides ample capacity for a 20-year design life. Due to the existing site and topological constraints, however, implementation and construction of the roundabout may be difficult. The roundabout option also requires a significant amount of new right-of-way. Figure 5 shows a conceptual rendering of the recommended intersection configuration. Actual design may vary from that shown in the figure.

FIGURE 5: RECOMMENDED CONCEPTUAL CONFIGURATION

Dern Spring Creek Preliminary Traffic Engineering Report Addendum · 2017-10-02 · Dern / Spring...

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