20190397_R-2566B CP 4A Additional Information 5-17-17_20170522

Project R-2566B
Additional Information (May 17, 2017)
Discussion of Need for the Proposed Climbing Lane
WHAT: NCDOT proposes extending the southbound climbing lane south of Broadstone Road for a
distance of approximately 5,000 feet. The existing southbound climbing lane is from station 180+00 to
station 202+00 (2,200 feet). The proposed climbing lane is from station 178+00 to station 250+00 (7,200
feet).
WHY: The extended climbing lane is proposed to address operational and design concerns. Also, there is
a safety need for a climbing lane in this area. A secondary benefit is that a climbing lane brings the road
up to current design standards.
Need 1: Operational and Desi�n Concerns
A. The climbing lane is warranted based on AASHTO guidelines (three criteria are listed on page 3-127 of
the AASHTO Green Book):
1. Overall volume criteria:
o Threshold: Warranted if there are a total of 200 vehicles per hour (vph) up-grade.
o Project: The traffic forecast projects 740 vph in the 2040 Build scenario.
2. Truck volume criteria:
o Threshold: Warranted if there is an up-grade truck flow rate of 20 trucks per hour.
o Project: The traffic forecast projects 6% trucks (4% duals + 2% TTSTs), for a total of 45
trucks in the 2040 Build scenario (15 TTST + 30 duals). Major sources of trucks along the
corridor include the quarry, concrete plant, and asphalt plant.
Speed or level of service (LOS) reduction criteria:
o Threshold: Warranted if there is either (a) 10 mph reduction in speed for heavy trucks,
or (b) LOS E or F on the grade, or (c) reduction of LOS by two or more levels.
o Project: The average upgrade from Broadstone to Old Schull's is 4% for 5400 feet. Per
AASHTO (Figure 3-28) this shows an anticipated reduction in speed approaching 25 mph.
e. The climbing lane will aid in climbing sight distance for southbound traffic.
Stopping Sight Distance requirements have been met through the climbing lane section. The
minimum stopping sight distance for horizontal and vertical curves is 495' for posted speed of
55 mph and 570' for design speed of 60 mph.
o The horizontal alignment through this section meets a 60 mph design speed except from
station 185+17 to 191+77, where it meets the 55 mph posted speed requirements. This
radius was not flattened to minimize impacts and higher cost due to associated
extensive cut into the mountainside.
o The vertical alignment through this section meets a 60 mph design speed except from
station 185+20 to 194+25, where it meets the 55 mph posted speed requirements. The
grade was not changed the additional 1%z feet necessary to minimize impacts and
higher project costs due to associated fills and right of way impacts.
Project R-2566B 1 May 17, 2017

• Passing Sight Distance is not met. The passing lane will aide traffic safety in the southbound
direction.
• It is likely that the existing climbing lane may be underutilized because drivers of slow-moving
vehicles have difficulty merging back into faster traffic that has accumulated behind. Due to the
short length of the climbing lane, accumulated traffic may not have had sufficient distance to
pass the slow-moving vehicles when the climbing lane ends.
Need 2: Improved Safety
A. Safety benefits of climbing lanes:
The Highway Safety Manual (based on researched sponsored by FHWA) recommends a crash
modification factor of 0.75 (or a 25% reduction) for total crashes in both directions of travel throughout
the extent of the climbing lane where climbing lanes are warranted. Additional research sponsored by
Michigan DOT reports a crash reduction of 33%.
e. A relatively small gap between the 4-lane section and the climbing lane may be counter to driver
expectations, resulting in increased safety concerns.
• This gap would require slower moving vehicles to make additional lane shifts which creates
additional conflicts.
• Leaving a gap may create a new safety situation which currently does not exist.
• If the project is built to include a gap between the Broadstone Road intersection and the
climbing lane, and if this design creates safety problems as anticipated, it would be difficult to
retrofit a"fix" at a future time.
• Current congestion during peak periods constrains speeds and speed differentials between
vehicles. As congestion is reduced and speeds increase correspondingly, the differential of
vehicle speeds between slow-moving trucks and other traffic is likely to also increase.
C. Crash data for this corridor:
Traffic volumes from 2003-2008 were similar to projected 2040 traffic volumes. Traffic volumes
decreased in the 2008-2014 period.
➢ There were 43% more crashes and only 20% more vehicles during the 2003-2008 period
compared to the 2009-2014 period. If traffic volumes increase in future years, as
projected, it is reasonable to expect that crashes would increase by a similar rate as
experienced in the past. The relationship between traffic volumes and traffic crashes is
often not linear, particularly as a roadway approaches capacity.
➢ During the 2003-2008 period, the total crash rate, non-fatal injury crash rate, and wet
crash rate exceeded the critical crash rate.
• Several specific deficiencies on NC 105 contribute to crashes:
➢ The paved shoulder is narrow (1-2 feet). Improving the clear zones would give vehicles
who depart the road an opportunity to recover or stop without crashing, and may reduce
the number of rear end crashes by providing space to maneuver if drivers encounter a
stopped vehicle unexpectedly.
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➢ There are some horizontal and vertical curves that limit sight distance, both along NC 105
and at some intersections. This is particularly dangerous in areas with a high number of
rear end crashes that involve vehicles stopped in the through lanes waiting to turn left.
➢ Scattered development and driveway frequency contributes to the pattern of rear end
crashes. Along NC 105, many businesses have pull-in parking, multiple driveways, or
open frontage that allows vehicles to enter into the parking lot along the entire property
length.
The majority of crashes were in the southbound direction (updated data, 2/1/11— 1/31/16).
➢ 66% of the crashes from just south of the NC 105/Broadstone Road intersection to the
approximate end of the current climbing lane occurred in the southbound direction.
➢ Discounting animal crashes, the percentage is 75%.
Secondary Benefit: Current Desi�n Standards
The road has been brought up to current design standards in the following ways:
• Superelevation was upgraded to accommodate a 60mph design speed.
• Provided 6' paved shoulders (existing paved shoulders are 2' wide, minimum is 4' wide).
• Increased climbing lane from 2,600' to 7,400' to allow for improved climbing of slow moving
vehicles in southbound direction.
• Realignment of southern Old Schull's Road intersection to provide improved sight distance and
reduce the intersection skew.
• Closure of the northern Old Schull's Mill Road intersection due to the skew, limited sight
distance, and safety concerns.
Outstanding Questions Following the Merger Meeting
The following questions were raised during the March 2017 CP 3& CP 4A Merger meeting.
• Request for additional data supporting the need for the proposed climbing lane
➢ Provided on pages 1-2 of this document
• Explanation of how the climbing lane was proposed to meet design criteria
➢ Provided on pages 1-2 of this document
• Consideration of design exceptions
➢ The proposed design improves the design criteria of the existing road to address safety
concerns, and has not requested any design exceptions
• Additional minimization measures
➢ Minimization measures were summarized in the CP 3& CP 4A Merger packet. Additional
minimization measures will be considered during final design and will be discussed with
the Merger Team as part of CP 4B & 4C.
• Consideration to shift the alignment further west (away from the river) in the section just south
of Broadstone Road
➢ The current design is a Best Fit alignment, as agreed to in CP 2, that stays out of the 100
year floodplain. Further shifting away from the river is not recommended due to the
higher relocation impacts and anticipated cost of a cut into the mountain
• Detail on stormwater design and potential consideration and commitments for specific
treatments
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➢ NCDOT will discuss specific designs and commitments with the Merger Team as part of
CP 4B & 4C
• Information on how Section BA ties with Section B
➢ NCDOT will determine the detailed interaction between the two sections during final
design
• Detailed geotechnical report
➢ NCDOT has provided a preliminary recommendation, which is subject to change during
final design as further investigation is performed. Based on the current design and
considering geotechnical conditions through the corridor, retaining walls are more likely
to be used to minimize fills rather than to minimize cuts.
• Potential treatments for wall cuts
➢ This has not been determined to be needed based on the current proposed design
Project R-2566B 4 May 17, 2017