Memorandum

Date:    January 9, 2013

To:         Boston Region Metropolitan Planning Organization

From:   Seth Asante, MPO Staff

Re:         Traffic Signal-Retiming Study for Route 2 in Concord and Lincoln

1         executive summary

This study provided sufficient information to assess the signal-timing issues in the Route 2 corridor caused by reconstruction of the Route 2, Route 2A, and Cambridge Street intersection. The analysis presented herein—along with the existing construction and permit jobs—will become part of a coordinated effort to improve traffic flow throughout the corridor. The traffic signal-retiming strategy would improve traffic flow over the short term, and would function only during the construction stage. After construction is complete, traffic flows would readjust to reflect changes in the highway network; and the MPO staff believes that post-construction traffic signal retiming should be conducted to reflect these changes.

MassDOT and the Boston Region Metropolitan Planning Organization (MPO) collected or provided operational, geometric, and safety data to evaluate existing and retimed conditions. The six signalized intersections were retimed in the corridor. Staff developed two new timing plans for this study: Option 1 consists of retiming and coordinating the existing traffic signal system; while Option 2 involves installing geometric improvements in addition to the retiming and coordinating.

This memorandum is organized into six sections:

• Section 1—Executive Summary
• Section 2—Background and Scope of Work
• Section 3—Data Collection
• Section 4—Evaluation of Existing Conditions
• Section 5—Development of New Timing Plans
• Section 6—Recommendations

1.1      Findings of Analysis

• Existing conditions indicate that the signalized intersections in the study area operate at or above capacity during peak periods because of high traffic demand.


• The following side streets experience long traffic delays and queues during peak periods:
  
  
  • Sudbury Road – northbound traffic
  • Walden Street – southbound traffic
  • Bedford Road – southbound traffic
  
  
• The left-turn traffic queue on Route 2 at the Main Street intersection frequently extends to the main travel lanes, disrupting traffic flow.


• Traffic signal retiming alone cannot offer significant benefits, as there is severe congestion and queuing throughout the Route 2 corridor and on some side streets.


• In addition to signal retiming, the following geometric improvements are necessary to improve traffic conditions:
  
  
  • Construction of a southbound left-turn lane on Bedford Road at Route 2
  • Construction of a northbound right-turn lane and a southbound left-turn lane on Sudbury Road
  • Construction of a westbound double left-turn lane on Route 2 at Main Street
  
  
• MPO staff recommends Option 1, retiming and coordinating existing traffic signal system, as a short-term solution to alleviate congestion. (See Appendix F for Option 1 retiming plans.)


• MPO staff recommends that MassDOT Highway Division District 4 consider Option 2, geometric improvements and signal retiming, as a medium-term solution.

2         background and scope of work

The arterial segment of Route 2 in Concord and Lincoln was selected for study because the Boston Region MPO’s LRTP identified Route 2 as one of the priority arterial segments in need of maintenance, safety, and mobility improvements. This segment was a high priority for improvement for MassDOT Highway Division District 4 because of serious congestion and safety issues. To help identify solutions for addressing problems in priority arterial segments, an arterial segment study was included in the federal fiscal year (FFY) 2013 Unified Planning Work Program (UPWP).¹

2.1      Study Area and Purpose

The approximately 5.5-mile study area is comprised of Route 2 from the Baker Avenue Extension in Concord to Bedford Road in Lincoln (Figure 1). The purpose of this study was to retime six traffic signals in the study area in order to improve traffic operations on Route 2 during reconstruction of the intersection of Route 2, Route 2A, and the Cambridge Turnpike at Crosby Corner (Figure 1). Construction, which began in spring 2012 and should end in spring 2016, is expected to affect traffic flow on Route 2 in Concord and Lincoln. At the time of this writing, mitigation work, such as erosion control, relocation of utility lines and poles, excavation, and pothole repair is underway. The study also examined the effects of the retiming on traffic flow in the arterial segment. MPO staff conducted this study, working closely with the MassDOT Highway Division District 4.

We excluded the Route 2, Route 2A, and Cambridge Turnpike intersection from this study based on discussions with MassDOT Highway Division, as this intersection is currently under construction. This is only one section in the entire study area. In addition, the Concord Rotary, located on the western end of the study area (Figure 1), was excluded from the study because a proposed project would replace the existing Concord Rotary with a highway interchange. Presently, Concord Rotary traffic queues affect traffic on Route 2, particularly in the vicinity of the Route 2 and Baker Avenue Extension intersection.

2.2      Scope of Work

The project’s work included data collection, assessment of existing conditions, and development of new timing plans and improvements. MassDOT and MPO staff collected the data; MPO staff conducted the assessment of existing conditions and developed new timings. The six intersections whose traffic signals were retimed are, from east to west (Figure 2):

• Route 2 and Bedford Road
• Route 2 and Route 126 (Walden Street)
• Route 2 and Sudbury Road
• Route 2 and Old-Road-to-Nine-Acre-Corner
• Route 2 and Main Street
• Route 2 and Baker Avenue Extension

3         data collection

Data used to evaluate existing conditions and develop new timing plans was either collected in the field or obtained from other sources such as MassDOT traffic signal and crash databases. The data collected included:

• Turning-movement counts (TMC) for the study intersection were conducted during the AM peak travel period (7:00 AM to 9:00 AM) and the PM peak travel period (4:00 PM to 6:00 PM) on weekdays during November 2012. Heavy vehicles (vehicles with six or more tires), including school buses, transit buses, and trucks, were counted separately. Automatic traffic recorder (ATR) counts conducted in 2012 were obtained from MassDOT’s Highway Division for three locations in the study area. The ATR counts were obtained through recorders over a period of 48 or more hours. (See Appendix A for complete ATR and TMC data.)


• Pedestrian counts for the study intersections were conducted simultaneously with the TMCs. MPO staff also took an inventory of pedestrian and bicycle amenities—such as curb cuts for wheelchairs, crosswalks, sidewalks, pedestrian signals, and user-activated push buttons—provided at study intersections.


• The MassDOT Highway Division provided traffic signal-timing plans and phase sequences of the study intersections. The Highway Division also provided as-built traffic signal plans or file drawings of each study intersection. (See Appendix B for signal-timing plans and as-built traffic signal plans.)


• MPO staff performed field reconnaissance to observe queue lengths.


• Crash data for the Route 2 intersections were obtained from MassDOT.

4         Evaluation of Existing Conditions

It was important to understand existing traffic characteristics within the study area—including number and rates of crashes, delays, and queues—prior to developing new timing plans.

4.1      Roadway

Route 2 is under the jurisdiction of MassDOT and generally runs in an east-west direction (Figure 1). It is functionally classified as a principal arterial roadway. Route 2 is part of the national highway system (NHS), and as such is a federal-aid-eligible roadway. In the study area, Route 2 has two travel lanes in each direction—and exclusive turn lanes—which are wider at the signalized intersections. The posted speed limit on Route 2 is 45 miles per hour (mph), from the Bedford Road intersection in Lincoln to the Baker Avenue Extension intersection in Concord. Route 2 has 6- to 8-foot shoulders on both sides of the roadway, and for the most part, a median barrier; however, the section between Sandy Pond Road and Oak Knoll Road has no shoulder or median. There are no sidewalks or bicycle lanes on Route 2.

4.2      Intersections

The major intersections on Route 2 are controlled by traffic signals. Figure 2 shows the configuration of the six signalized intersections that were studied. Here, crosswalks and pushbutton pedestrian signals have been installed and are functioning well. The minor intersections in the study area are controlled by stop signs on side streets, where only right-turning movements are permitted. Pedestrians are prohibited from crossing Route 2 at unsignalized intersections that contain a median barrier.

4.3      Traffic, Pedestrian, and Bicycle Volumes

The three locations of the ATR counts on Route 2 are cited below and displayed in Figure 3.

• Route 2 east of Concord Rotary in Concord
• Route 2 west of Walden Street in Concord
• Route 2 east of Bypass Road

Based on the ATR counts, the average weekday daily traffic volumes range between 41,000 and 51,000 vehicles. The TMCs also are summarized in Figure 3. The TMCs do not reflect the traffic queues or traffic demand at the intersections because only vehicles that pass through the intersections were counted—vehicles already in queue at the end of counting period were not counted. This situation occurs because congestion and queues on Route 2 last significantly longer than the periods during which the TMCs were conducted. Estimates of the average number queued vehicles were determined during field visits. See Table 1 for the percentage of heavy vehicles at study intersections during peak periods when the TMCs were conducted. The table indicates that this percentage ranges between 2.0 and 3.0 percent, which is not particularly high for peak-period traffic conditions. Also, staff did not detect any roadway geometry—such as turning radii—that would inhibit truck traffic flow.

The percentage of heavy vehicles was higher on Main Street and Old Road to Nine Acre Corner compared to the other cross streets. This study did not investigate the reasons for the high percentage of heavy vehicles here because it was not study’s focus.

There were few pedestrians crossing Route 2 at the study intersections during peak periods (Table 2).

TABLE 1
Percentage of Heavy Vehicles at Intersections during AM and PM Peak Periods

TABLE 2
Pedestrian and Bicycle Counts at the Study Intersections

4.4      Crash Data

MPO staff used crash data obtained from the MassDOT Registry of Motor Vehicles (RMV) to evaluate safety at the study intersections. The RMV crash data cover the period from January 2006 through December 2010. For details of crashes—severity, manner of collision, and ambient light conditions—at each of the study intersections, see Table 3. The average crash rates were calculated per MassDOT’s methodology. The District 4 Highway Division’s average crash rate (published by MassDOT based on crash information queried on January 23, 2013) is 0.77 crashes per million entering vehicles at signalized intersections. Four of the study intersections have crash rates greater than or equal to the District 4 average for signalized intersections:

• Route 2 and Bedford Road
• Route 2 and Walden Street (Route 126)
• Route 2 and Main Street
• Route 2 and Baker Avenue Extension

At each of these four intersections, the most prevalent crash type was rear-end collisions. The majority of crashes occurred on Route 2 rather than on the cross streets. The high number of rear-end collisions on Route 2 appears to result from unexpected stops because of traffic queues at the signalized intersections and high travel speeds. (See Appendix C for collision diagrams and crash-rate worksheets.)

TABLE 3
Crash Summaries and Rates for Study Intersections (2006–2010)

4.5      Traffic Operations

Using the data collected, plus observed conditions in the field, MPO staff built a network for the AM and PM peak periods using Synchro Studio 8 traffic software. The TMC data, existing phases and sequences, network offsets, and phase intervals and splits were input to a model determined to the arterial levels of service (LOS), delays, and queues at the signalized intersections. LOS and capacity analyses were conducted on the 2012 existing conditions and calibrated to the observed operating conditions to provide a baseline scenario.

Two time settings were evaluated for existing conditions—AM and PM peak periods. No consideration was given for special events or weekend timing because there are no shopping malls or major sports facilities in the Route 2 corridor—the primary cause of congestion was high traffic volume resulting from commuter work trips.

Analyses were conducted in a manner consistent with the Highway Capacity Manual (HCM) 2010 methodology, which expresses the quality of driving conditions at signalized intersections it in terms of LOS ratings A through F:

• LOS A represents the best operating conditions, or little to no delay.
• LOS F represents the worst operating conditions, or very long delay.
• LOS E represents an intersection operating at capacity, or at the limit of acceptable delay.

Based on the Highway Division’s existing signal-timing plan, traffic signals at the following intersections operate with coordination during peak periods:

• Route 2 at Baker Avenue Extension
• Route 2 at Main Street
• Route 2 at Old Road to Nine Acre Corner
• Route 2 at Sudbury Road

Traffic signal coordination occurs when a group of two or more traffic signals are working together so that cars moving through the group will make the least number of stops possible. In order for this to happen, each traffic signal in the group must allow a green light for all directions of travel during a fixed time period. Coordination operations are in effect during the morning peak period from 6:30 AM to 9:30 AM and during the evening peak period from 3:00 PM to 7:00 PM. The coordinated cycle lengths are 110 seconds for the AM peak period and 120 seconds for the PM peak period. The coordinated traffic signal system uses a global positioning system (GPS) timer to keep the traffic signals perfectly synchronized.

Traffic signals at the intersections of Route 2 and Walden Street and Bedford Road operate alone; they are not coordinated because of the long distances between them and the other signals.

4.5.1   Operating Problems

MPO staff observed the following operating conditions in the field:

• During the AM peak period, long traffic queues develop on the Route 2 eastbound approaches at the signalized intersections.


• At the Baker Avenue Extension intersection, the Route 2 eastbound queue extends westerly into the Concord Rotary.


• At the Main Street intersection, the Route 2 eastbound queue sometimes extends westerly into the Baker Avenue Extension intersection.


• At the Sudbury Road and Walden Street intersections, the Route 2 eastbound queue extends westerly to Fairhaven Road and the bridge over the Sudbury River.


• At the Bedford Road intersection, the Route 2 eastbound queue extends westerly to Orchard Lane.


• Similarly, during the PM peak period, long traffic queues develop on the Route 2 westbound approaches at the signalized intersections.
  
  
  • The queue at the Concord Rotary extends easterly into the Baker Avenue intersection. Westbound traffic merging onto Route 2 from Elm Street contributes to this queue. 
  
  
• At the Baker Avenue Extension intersection, the Route 2 westbound queue extends easterly into the Main Street and Old Road to Nine Acres Corner intersections.


• At the Sudbury Road and Walden Street intersections, the Route 2 westbound queue extends easterly to the Fitchburg commuter rail bridge and Sandy Pond Road.


• At the Bedford Road intersection, the queue on Route 2 westbound extends easterly for about one-half mile.


• Some of the side streets experience long queues, and it appears that not enough green times are allocated to the side streets, especially at:
  
  
  • Main Street northbound
  • Sudbury Road northbound
  • Walden Street southbound
  • Bedford Road southbound
  
  
• During peak periods, left-turn queues on Route 2 at the Main Street and Baker Avenue Extension intersection extend into the main travel lanes, interrupting traffic flow.

Tables 4 and 5 below present results of the intersection-capacity analysis for the existing conditions in terms of LOS, delays, and queues. The analysis shows that the signalized intersections are operating at or above capacity during peak periods. The analysis also indicates long queues on Route 2 and some of the side streets during peak periods. (See Appendix D for LOS analysis worksheets.)

5         Development OF New Timing Plans

MPO staff developed two timing plans and compared them with the existing timing plans put in place by MassDOT Highway Division District 4.

TABLE 4
AM Peak-Hour Level of Service

*Geometric improvement.

¹ Delay in seconds per vehicle.

² 95th percentile queue length in feet.

# means that the 95th percentile volume exceeds capacity. m means upstream metering is in effect.

Source: Central Transportation Planning Staff.

TABLE 5

PM Peak-Hour Level of Service

* Geometric improvement

¹ Delay in seconds per vehicle.

² 95th percentile queue length in feet.

# means that the 95th percentile volume exceeds capacity. m means upstream metering is in effect.

Source: Central Transportation Planning Staff.

5.1      Option1: Retiming and Coordinating of Existing Traffic Signal System

Option 1 consists of retiming and coordinating the existing traffic signal system using the methodology discussed earlier. For safety, enough time was allocated for pedestrians to cross Route 2 or a side street from curb to curb. Known as the “pedestrian clearance interval,” this is represented by the flashing DON'T WALK or upraised-hand signal. As with pedestrian crossings, adequate time was allocated for cross-street and left-turning traffic.

5.2      Option 2: Geometric Improvements and Retiming and Coordination

Option 2 consists of geometric improvements in addition to the signal retiming and coordination described in Option 1. Proposed new construction entails:

• Southbound left-turn lane on Bedford Road
• Northbound right-turn lane on Sudbury Road
• Southbound left-turn lane on Sudbury Road
• Second westbound left-turn lane on Route 2 at Main Street

Tables 4 and 5 below present results of the intersection-capacity analysis for the two options in terms of LOS, delays, and queues. (See Appendix D for the LOS analysis worksheets for the two options.)

There appears to be enough space in the right-of-way for constructing these geometric improvements. For each of these, a 200-foot turn lane would be sufficient to improve traffic operations. In addition, they each would require new traffic signal heads to control the turn lane. These improvements would cost between $500,000 and $750,000, except for the second westbound left-turn lane on Route 2 at Main Street, which would cost between $750,000 and $1.0 million.

5.3      Time-of-Day Signal Settings

The final component to the new timing plan is the time-of-day signal settings. These settings determine the optimal timing plan for each hour of a typical weekday. The time-of-day signal settings were obtained by evaluating the 24-hour ATR count data from three locations on Route 2. (See Appendix E for signal settings for the peak- and off-peak periods.) The peak-period operations are:

• AM peak period: 6:30 AM to 9:30 AM
• PM peak period: 3:30 PM to 7:00 PM

5.4      Measures of Effectiveness

To measure the effectiveness of the timing plans, Synchro 8 was used to evaluate arterial LOS—in terms of delay, travel time, and speed—for the two options described above. (See Table 6 below.)

• During the AM peak period, signal optimization yields about 8 percent improvement in travel time eastbound; the improvement increases to 10 percent with the addition of geometric improvements. Similarly, travel speed increases by 5 percent with signal optimization and by 11 percent with the addition of geometric improvements.


• During the PM peak period, signal optimization yields about 4 percent improvement in travel time westbound; the improvement increases to 9 percent with the addition of geometric improvements. Similarly, travel speed increases by 5 percent with signal optimization and by 11 percent with geometric improvements.


• Overall, the study shows that signal retiming would offer benefits in the Route 2 corridor, but it is not sufficient to stem the severe congestion and queuing throughout the corridor. For this, geometric improvements also are necessary.


• Geometric improvements would benefit traffic on the side streets where they were recommended. At the intersection of Sudbury Road, levels of service would improve from LOS E or F to LOS D for both the northbound and southbound approaches. At the Bedford Street intersection, levels of service would improve from LOS F to LOS E or D.

TABLE 6

Route 2 Signal-Retiming Results: Arterial Levels of Service

6.        Recommendations

Short-Term Solution:

1. MPO staff recommends Option 1, retiming and coordination of the existing traffic signal system, to alleviate congestion in the Route 2 corridor for the near term. (See Appendix F for Option 1 Timing plans.)

Medium-Term Solution:

1. MPO staff recommends that MassDOT Highway Division District 4 consider Option 2, geometric improvements and retiming and coordination for the medium term.


2. Regarding Option 2, analysis shows benefits would be realized from the following construction:
   
   
   • A northbound right-turn lane and a southbound left-turn lane on Sudbury Road—This would improve traffic flow and alleviate queues on Sudbury Road during the AM and PM peak periods. The improvements would require widening the Sudbury Road approaches, and could be accommodated within the existing right-of-way.
   
   
   • A southbound left-turn lane on Bedford Road—This would improve traffic flow and reduce the length of AM and PM traffic queues on the approach. This improvement could be accommodated within the existing right-of-way.
   
   
   • A second westbound left-turn lane on Route 2 for traffic turning onto Main Street—This would improve traffic flow at the intersection during the AM and PM peak periods. It also would help prevent the westbound left-turn lane queue from extending into the westbound through lane, which causes congestion at the intersection.
   
   
   • This solution would require widening the Route 2 pavement within the existing right-of-way to accommodate the second left-turn lane, as well as widening a short portion of the Route 62 pavement west of Route 2 to accommodate a second westbound receiving lane. Currently, the existing Route 2 westbound exclusive-right-turn lane is highly underutilized and could be converted to a through-plus right-turn lane to limit the improvement to within the right-of-way.

SAA/saa

cc:  M. Karas, MassDOT District 4
J. Onorato, MassDOT District 4   C. Raphael, MassDOT District 4 P. Nelson, MassDOT Planning

Figures

1. Study Area
2. Study Intersections
3. Existing Turning Movement Counts and Average Daily Traffic

Appendixes