HomeMy WebLinkAboutLane Configuration on College St. from Main St. to 19th and Lane Configuration at 23rd.pdf
Commission Memorandum
REPORT TO: Honorable Mayor and City Commission
FROM: Bob Murray, Project Engineer
Rick Hixson, City Engineer
Chuck Winn, Assistant City Manager
SUBJECT: College Street – Main Street to S. 19th Avenue – Lane Configuration and
23rd and College Intersection Control
MEETING DATE: August 22nd, 2011
AGENDA ITEM TYPE: Action
RECOMMENDATION: Motion and vote to approve Alternative 3 as presented in the document
“Technical Memorandum, College St-Main to 19th Roadway Configuration”.
BACKGROUND: The Montana Department of Transportation (MDT) has initiated the design
for the reconstruction of College Street from 19th to Main. They have hired the consulting firm
of Robert Peccia and Associates (RPA) to provide the design services for the project.
The 2007 Transportation Plan recommended that this section of College be improved to a 5-lane
section (4 through lanes with a raised median and turn bays at the intersections). A more
detailed analysis has shown that only 3 lanes (2 through lanes with a raised median and turn bays
at the intersections) is required to adequately handle the projected traffic demands from Main to
23rd Avenue. The portion of road from 23rd to 19th still needs the larger section. Both a signal
and a multi-lane roundabout would provide adequate level of service for the intersection of 23rd
and College but the roundabout has a higher initial cost, requires more right-of-way and would
require pedestrian signals making the conventional traffic signal a more attractive option.
MDT and RPA are working towards completing the EA and an application for a TIGER grant
which are due in October. In order to move forward with those tasks, the final lane configuration
and intersection control must be decided upon which is the purpose of this hearing.
UNRESOLVED ISSUES: Lane configuration and intersection control
ALTERNATIVES: As suggested by the City Commission.
FISCAL EFFECTS: The project is being funded through a combination of Urban Funds and
Impact Fees.
Attachments: Technical Memorandum
Report compiled on: 8/10/11
310
Prepared For:
MONTANA DEPARTMENT OF TRANSPORTATION
AND THE CITY OF BOZEMAN
Prepared By:
ROBERT PECCIA & ASSOCIATES
August 10, 2011
Technical Memorandum
College St – Main to S 19th
Roadway Configuration
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TABLE OF CONTENTS
TABLE OF CONTENTS ......................................................................... 2
EXECUTIVE SUMMARY ....................................................................... 3
INTRODUCTION AND PURPOSE ............................................................ 4
TRAFFIC ANALYSIS METHOD ............................................................... 5
ROADWAY CONFIGURATION ALTERNATIVES .......................................... 6
PREFERRED ALTERNATIVE ................................................................... 8
ROUNDABOUT VS. TRAFFIC SIGNAL COMPARISON .................................. 9
APPENDIX A: ROADWAY CONFIGURATION ALTERNATIVES ..................... 11
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EXECUTIVE SUMMARY
The purpose of the memorandum is to present the pre‐
ferred lane configuration for the portion of College
Street to be reconstructed with the Montana Depart‐
ment of Transportation (MDT) project College St. –
Main to S 19th – Bozeman.
Several alternatives were evaluated and are presented
briefly herein. The final recommended alternative is a
three‐lane roadway from the intersection of College
Street and W Main Street to the intersection of College
Street and S 23rd Avenue and a five‐lane roadway from
that intersection to the end of the project at the intersection of College Street and S 19th Avenue. This
memorandum will discuss the process of selecting the chosen alternative, the preliminary costs and a
description of each roadway configuration considered.
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INTRODUCTION AND PURPOSE
Robert Peccia and Associates (RPA) was selected by the MDT
and the City of Bozeman to prepare plans for the reconstruc‐
tion of College Street between W Main Street and S 19th
Avenue. The most critical decision to be made in the devel‐
opment of the project is the proposed lane configuration of
the roadway.
According to the Greater Bozeman Area Transportation Plan
(2007 Update) this portion of College Street is classified as an
urban arterial and is recommended to be upgraded to a five‐
lane roadway with two travel lanes in each direction, bike
lanes on each side, curb and gutter, boulevard, sidewalk and
a raised median. The traffic information used in determining
the project needs identified in the Transportation Plan was
based on 2005 traffic data and represents a time of substan‐
tial community growth, just prior to a significant economic
slowdown. Additionally, modifications to the major street network in Bozeman have provided attractive
alternative routes to College Street for traffic moving to and from the south side of Bozeman and Mon‐
tana State University. For these reasons, it was determined that the recommendations made in the
Transportation Plan for this roadway should be reevaluated, taking into consideration changes in traffic
conditions on College Street as discussed above.
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TRAFFIC ANALYSIS METHOD
In the spring of 2011, RPA collected traffic volume
data and turning movement counts for all of the ma‐
jor public and private intersections within the project
limits. Using this data, RPA estimated future traffic
usage for corridor, using the MDT projected yearly
growth rate of 3.2% for a design life of 25 years. This
yearly growth rate was applied throughout the pro‐
ject corridor and is based on historic traffic growth
characteristics for College Street.
It must be noted that using this growth rate and at‐
tributing it to this segment of roadway may not be an accurate portrayal of conditions that will occur in
the future. Development is unlikely to occur uniformly in the Bozeman area. Ultimately, future traffic
growth along College Street is likely to be limited by the conditions of the major intersections, i.e. S 19th
Avenue and W Main Street. These intersections have limited capacity based on their current configura‐
tions as vehicles are restricted by the queuing for the signals and the “green time” each signal provides
for those wishing to enter College Street.
New routes in and around Bozeman have been and will continue to be improved and will likely draw
some traffic from the surrounding area. The recent expansion of Garfield Street, for example, draws
traffic away from College Street and the busy College Street/S 19th Avenue intersection. As more road‐
ways are added or improved, motorists will alter their routes and distribute traffic away from busy
corridors.
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ROADWAY CONFIGURATION ALTERNATIVES
Utilizing the traffic modeling software Synchro and MDT design
standards, RPA used the afore‐mentioned traffic volume projec‐
tions to evaluate the ability of several travel and turn lane
configurations to accommodate the anticipated traffic.
The existing traffic conditions indicate that the intersection with
S 23rd Avenue experiences a LOS F during AM and PM peak
hours. The traffic turning movement data and the Synchro mod‐
eling revealed two major traffic movements at the intersection
with S 23rd Avenue. During the AM peak hour, there is a higher
volume of vehicles traveling southbound on S 23rd Avenue and
making a left turn onto College Street. Currently this intersection
is controlled only by a stop sign on S 23rd Avenue. Some of this
traffic is from development northwest of Bozeman that is col‐
lected on Babcock Street, and some results from motorists attempting to bypass the busy S 19th Avenue.
The second high‐volume movement of traffic is during the PM Peak hour when traffic returns from Col‐
lege Street to S 23rd Avenue. During this time period there are a high number of westbound right turns
from College Street onto S 23rd Avenue. Any suggested improvements to this intersection should con‐
sider these two high‐volume movements.
It should be noted that the installation of a traffic signal or roundabout at the intersection at S 23rd Ave‐
nue will likely increase the usage of the intersection due to the decreased peak hour delays.
The lane configurations modeled are shown in the table below.
Table 1: Roadway Configuration Alternatives
Alternative W Main to S 23rd S 23rd to S 19th College/S 23rd Intersection Traffic Control
1 3‐lane 3‐lane Signal
2 3‐lane 3‐lane Single‐Lane Roundabout
3 3‐lane 5‐lane Signal
4 3‐lane 5‐lane Multi‐Lane Roundabout
5 5‐lane 5‐lane Signal
6 5‐lane 5‐lane Multi‐Lane Roundabout
Aerial photos showing the conceptual lane delineations and preliminary raised median layouts for Alter‐
natives 1‐4 are included in Appendix A of this memorandum. As stated above, these delineations are
conceptual; turn bay lengths and locations and raised median breaks will be finalized as plans develop.
The intent of the displays is to depict the overall lane configuration concepts. Bike lanes in each direc‐
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tion, sidewalk on the north and a bike/pedestrian path to the south will be provided with all of the al‐
ternatives. A brief description of the roadway configurations follows:
Alternative 1: Two travel lanes would carry traffic on College Street, with intermittent left‐turn lanes
at major private and public approaches and right‐turn lanes at W Main, S 23rd Avenue and S 19th Av‐
enue. Alternatives 1 and 2 are the lowest capacity roadways presented. A traffic signal would be at
the S 23rd Avenue intersection. Right‐of‐way and construction costs for this Alternative would be
approximately $4.8 million.
Alternative 2: Same configuration as Alternative 1 but with a single‐lane roundabout at 23rd Avenue.
A right slip lane from College Street to S 23rd Avenue would increase capacity of the roundabout in
the evening peak traffic hours. The cost would be approximately $5.3 Million.
Alternative 3: Two travel lanes would be constructed between W Main Street and S 23rd Avenue,
with an additional eastbound lane beginning just prior to the S 23rd Avenue intersection to provide
two eastbound lanes through the intersection. Five lanes would continue to the intersection with S
19th Avenue. The westbound second lane would be a dedicated right‐turn onto S 23rd Avenue and
would end at the intersection. This Alternative would accommodate dual left turn lanes from S 19th
Avenue onto westbound College Street. The additional left lane helps alleviate traffic backing up on
S 19thAvenue. The cost of this alternative is $5.0 Million.
Alternative 4: Same configuration as Alternative 3 but with a multi‐lane roundabout at S 23rd Ave‐
nue. The roundabout would require pedestrians to cross more than one lane of traffic, so
pedestrian‐actuated signals would be required as discussed in the Roundabout versus Traffic Signal
Comparison section of this memo below. The pedestrian signals increase safety and pedestrian func‐
tionality of the intersection, but do negatively affect traffic flows. The multi‐lane roundabout
provides a free right movement for the heavy afternoon volume of traffic moving from westbound
College Street northbound on to S 23rdAvenue. Also, the dual lanes increase capacity for the morn‐
ing eastbound traffic along College Street. The cost would be approximately $5.8 Million.
Alternative 5: A full five‐lane configuration between W Main Street and S 19th Avenue would in‐
clude two travel lanes in each direction, a median with intermittent left‐turn bays, and a bike lane in
each direction. Alternatives 5 and 6 are the highest capacity roadways presented. A signal would be
at the S 23rd Avenue intersection. This alternative again allows for dual left‐turn lanes from S 19th
Avenue onto westbound College Street. As mentioned previously, the traffic volumes anticipated
on this roadway in the future do not warrant a five‐lane section.
Alternative 6: Same configuration as Alternative 5 but with a multi‐lane roundabout at 23rd Avenue.
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PREFERRED ALTERNATIVE
It is recommended that a three‐lane section be implemented between Main Street and S 23rd Avenue
and a five‐lane section between S 23rd Avenue and S 19th Avenue. In addition, dual northbound left‐turn
lanes should be incorporated in the intersection with S 19th Avenue to accommodate traffic turning left
onto College Street.
Traffic volumes recorded in 2011 and projected out to the year 2036 revealed that a five‐lane roadway
between N Main Street and S 23rd Avenue as recommended by the Transportation Plan may not be nec‐
essary. Future projected ADT for College Street is approximately 15,000 vpd west of S 23rd Avenue and
20,000 vpd east of S 23rd Avenue. According to the Transportation Plan, theoretical capacity for a 3‐lane
facility is between 18,000 and 22,500 vpd. However, the capacity of College Street will ultimately be
affected by the performance of the major intersections.
During the morning peak hours there is a high volume of traffic traveling eastbound on College Street
and southbound on S 23rd Avenue due to motorists traveling to the MSU campus. Adding an additional
through lane just west of S 23rd Avenue allows for a shorter green phase for that leg of the intersection,
allowing a higher volume of traffic to enter the roadway from S 23rd Avenue; thereby reducing queuing
length along College Street.
Conversely, during the peak afternoon hours, heavy traffic returns westbound on College Street with
high right‐turn movements on to S 23rd Avenue. The College Street/S 19th Avenue intersection currently
is projected to carry a high volume of turn‐left vehicles onto College Street which results in long queue
lengths along S 19th Avenue. Personnel from the City of Bozeman indicated that the latest construction
project upgrading S 19th Avenue provided enough width to stripe in dual left‐turn lanes along the south
leg of S 19th Avenue at this intersection. The additional westbound travel lane along College Street
would create an additional receiving lane that would allow for the dual left‐turn lanes. Synchro model‐
ing indicated a decrease of left‐turn queuing and an overall increase in intersection performance on S
19th Avenue significant enough to warrant adding the lane, especially if the changes to S 19th Avenue can
be implemented with striping only.
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ROUNDABOUT VS. TRAFFIC SIGNAL COMPARISON
Well‐designed and appropriately placed roundabouts can
provide several benefits over a traffic signal. In general, the
safety of an intersection is improved as conflict points and
speeds are reduced. Roundabouts allow for continuous traf‐
fic flow, reducing traffic disruption and vehicle emissions.
Alternatives 2,4 and 6 include a roundabout at the intersec‐
tion of College Street and S 23rd Avenue. ADA mandates
require that pedestrian signals be provided at roundabouts
where pedestrians are crossing more than one lane of traffic. Although this is an important safety fea‐
ture that greatly improves navigation through a roundabout for pedestrians, it must be noted that some
of the traffic and environmental advantages of the roundabout are reduced in areas of high pedestrian
traffic.
Both the traffic signal and the roundabout will accommodate the AASHTO WB‐67 tractor‐trailer for
through movements on College Street. A smaller design vehicle can be used to determine turning
movements within the roundabout and for the radii in a signalized intersection to minimize the size of
the intersection and reduce right‐of‐way needs.
The table on the following page compares some elements of an unsignalized roundabout versus a traffic
signal.
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Table 2: Roundabout vs. Traffic Signal Comparison
Traffic Signal Roundabout Safety Crash Frequency Greater potential for high‐angle crashes. Historically tend to decrease crash rates.
Crash Severity Higher due to higher speeds and higher speed
differential.
Lower due to lower speeds and lower speed
differential. Elimination of high‐speed T‐bone
(angle) crashes.
Driver Expectancy Conventional traffic control – drivers are familiar
with operation.
Local drivers are less familiar with operation.
Number of conflict
points
Vehicle to vehicle ‐ 32
Vehicle to pedestrian ‐24
Vehicle to vehicle – 8
Vehicle to pedestrian ‐ 8
Number of driver
decisions
Higher than roundabout since drivers need to be
aware of vehicles to the left, right and straight
ahead.
Reduced as drivers only need to be aware of
vehicles to their left at entry.
Traffic Calming Traffic speeds depend upon signal phase. Geometrics ensure lower speeds. Can provide
“gateway” that indicates a change in condi‐
tions.
Pedestrian Safety Presents more vehicle/bicycle conflict points. Pe‐
destrians cross with protected phase.
Vision impaired pedestrians disadvantaged
due to continuous traffic flow. Traffic Operations Trucks Accommodates trucks if curb radii designed to
truck turning movements.
Requires the use of a truck apron to allow
trucks to navigate.
Traffic Signing Typical intersection signing. More complex intersection signing, particular‐
ly for multi‐lane roundabouts.
Traffic Speed Not limited by geometrics. Speed on side roads
previously controlled by stop signs may increase.
Geometric features slow entering and circu‐
lating speeds.
Vehicle control Timing operations can control traffic flows, pla‐
tooning of vehicles.
Uncontrolled flow.
Access Control Restricted u‐turn capability. Allows for u‐turns to access limited‐access
approaches.
Pedestrian Operation Pedestrians familiar with use. May increase dis‐
tance pedestrians required to cross.
Splitter islands reduce crossing distance be‐
tween refuge points, pedestrians may be
unfamiliar with usage. R/W Right‐of‐Way Impacts Typically requires minimal R/W on each leg of in‐
tersection.
Requires more R/W than a signal. Cost Construction Relatively simple to install, contractors familiar
with installation.
More complicated construction.
Construction Cost Lower installation cost than roundabout. Higher initial construction cost.
Maintenance Cost Higher operational and maintenance costs (power,
LEDs, lighting, electrical equipment, pavement
markings, etc.)
Minimal operational and maintenance costs
(lighting, pavement markings, etc.) Community Impacts Community En‐
hancements
Community enhancements can be installed on the
perimeter of the intersection. Generally less aes‐
thetically appealing.
In addition to the perimeter the central island
may be developed as a “gateway” to a com‐
munity.
Environmental Bene‐
fits
Increase in fuel consumption and emissions due to
stopped and running vehicles during red light
phases.
Overall reduction in fuel consumption and
vehicle emissions since delay at the intersec‐
tion is reduced.
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APPENDIX A: ROADWAY CONFIGURATION ALTERNATIVES
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