Technical Memorandum


DATE:   January 18, 2018

TO:         Cara Seiderman, Transportation Program Manager,

                Cambridge, MA

FROM:   Casey-Marie Claude, MPO Staff

                Mark Abbott, MPO Staff

RE:         Bicycle Network Gap Feasibility Evaluation for Central Square


1          background

            2014 Bicycle Network Evaluation

In 2014, the Boston Region Metropolitan Planning Organization (MPO) staff conducted the Bicycle Network Evaluation, a regional study that resulted in a list of eleven locations designated as “high-priority” gaps based on how they scored against criteria used to assess their potential to improve bicycle connectivity.1 The gaps identified as the highest priority were those where an improvement project would have the greatest potential to improve the Boston region’s bicycle network goal of enhancing bicycle safety, continuity, and connectivity.

The purpose of this study is to build upon the original 2014 Bicycle Network Evaluation by assessing potential improvements to several high-priority gaps—such as the one found in Central Square—that could be considered for design and construction funding in future Transportation Improvement Program (TIP) cycles.

The outcomes of this study will include recommendations for appropriate types of bicycle facilities—for example, on-road bike lanes, protected bike lanes (cycle tracks), shared lanes, and shared-use paths—for each of the high-priority gaps selected for assessment. The findings and products of the study will support local, regional, and state planning efforts to provide a safe, convenient, continuous, and connected bicycle network in the metro Boston area.

2          Gap Selection

For this study, the Boston Region MPO selected three gaps from the list of eleven locations designated as “high-priority” gaps in the 2014 Bicycle Network Evaluation. MPO staff selected one gap from each category—small, medium, and long—based on criteria that included Massachusetts Department of Transportation (MassDOT) crash clusters, underserved/environmental justice communities, employment, town centers, central business districts, schools, universities, parks or open space, above-average numbers of future bicycle/pedestrian trips, and consistency with regional plans for bicycle transportation. The three locations approved by the MPO for study are:

Staff selected the location in Cambridge because it was the highest-scoring bicycle network gap in the small category that had not already been studied.

2.1      Gap Location and Study Area

Figure 1 displays the location of the Central Square bicycle gap, as originally identified in the 2014 study. The study area (blue oval) ran from the northeastern ends of the bicycle facilities on Western Avenue across Massachusetts Avenue to the Harvard Street bike lane to the north. In the map, a dashed red line indicates where, within the gap, bicycle facilities are not installed—starting southwest of Massachusetts Avenue at the end of the separated bicycle lane on Western Avenue, continuing north along Prospect Street until north of Broadway where bike lanes are striped for both directions of travel; the bike lanes end near Gardner Road as Prospect Street approaches the Hampshire Street intersection.

Prospect Street was initially identified as a priority for bicycle improvements because this street is the most direct connection between the Hampshire Street bike lanes and the Western Avenue separated bicycle lane. As mentioned above, there are bike lanes on Prospect Street from north of Broadway to south of Hampshire Street, near Gardner Road. When MPO staff began studying this gap, they pursued the idea of adding bike lanes to the remaining segments of Prospect Street from Massachusetts Avenue to Hampshire Street because this would provide a continuous path of bicycle facilities between Central Square and Inman Square. However, plans to improve Inman Square to the north and River Street to the south make it impossible to accurately anticipate travel patterns in the near future. It would be imprudent to recommend adding bike lanes to Prospect Street before the analyses can be informed by observed changes in travel behavior once Cambridge improves Inman Square and River Street. To address these concerns, MPO staff used two different approaches to study the gap in the Boston region bicycle network at Central Square.

Figure 1 – Map of the gap in the Boston region bicycle network at Central Square in Cambridge.


3          Gap Evaluation

Staff evaluated the Central Square bicycle gap in two parts: 1) a walking tour and assessment of the existing signed bicycle route through Central Square from where it starts at Inman Square to where Western Avenue and River Street meet south of Massachusetts Avenue; and 2) a full analysis of the potential for closing the gap by way of adding bike lanes to Prospect Street. This second effort will need to be revisited once Cambridge improves Inman Square and River Street because the current findings likely will change after construction is complete. Closing this Boston region bicycle network gap could potentially benefit many people. Central Square and Inman Square are both commercial areas and major destinations in Cambridge. Both squares are also relatively well connected to the bicycle network—the main exception being a lack of north-south bicycle facilities between the two locations.


 3.1     Improving the Existing Signed Bicycle Route

MPO staff joined City of Cambridge staff on November 14, 2017, for a walk audit of the signed bicycle route that travels through Central Square in Cambridge. The route connects Inman Square to the Boston University (BU) Bridge, which crosses the Charles River and connects to Boston. This signed route facilitates bicyclist travel through Central Square by directing bicycle traffic along streets identified by Cambridge as being comfortable for bicyclists. This route serves as an alternate north-south connection across Central Square with a less direct path to Inman Square than Prospect Street, but with many roadways that feature more space for cyclists, lower traffic speeds, and fewer conflicts with motor vehicles for bicyclists.

In order to improve the comfort and safety of the signed bicycle route in Cambridge, city and MPO staff identified several changes that could be made to the physical environment:

Shared Lane Markings

Including shared lane markings along the signed bicycle route reinforces bicyclists’ understanding that they are traveling along a route designated for bicycle travel. In this way, shared lane markings function as a second wayfinding resource, supporting the bicycle route signage. The shared lane markings also indicate to motorists that they should anticipate bicycle traffic along a specific roadway, reminding drivers to share the road. Norfolk Street north of Broadway is one street that could benefit from shared lane markings, while adding the markings at the start of both turning lanes where Inman Street meets Massachusetts Avenue could improve the intersection for road users. An exception to the shared lane marking suggestion is Bishop Allen Drive, of which only two blocks are included in the bicycle route. Adding shared lane markings for this short length could cause more confusion than clarity.

Alternately, the potential of adding shared lane markings on Inman Street southwest of Broadway should be explored. The roadway currently features what Cambridge staff referred to as “fog lines” to the left of the lane of parked cars, located on the right side of the street (Figure 2). This was added to encourage motorists to drive farther from parked cars. However, the striping causes confusion because it can be perceived as a bike lane, in spite of being too narrow and located directly within the path of opening car doors. Shared lane markings on this roadway could help all users understand that Inman Street does not include a separate travel way for bicyclists and that the roadway should be shared accordingly.

Figure 2
Inman Street “Fog Line”

Figure 2 – Image of the “fog line” on Inman Street in Cambridge.

Additional Signed Bicycle Route Branch

The purpose of the signed bicycle route is to help bicyclists who are less comfortable than others about riding, and/or who are not as familiar with Cambridge and need help navigating their way through Central Square and the surrounding area. For this reason, there is support in the Cambridge community for directing bicyclists along bicycle-friendly Western Avenue, which includes a separated bike lane and bicycle signals at intersections. People perceive that Western Avenue is a more comfortable route than Magazine Street for cyclists traveling south from Central Square to the Charles River. To encourage using Western Avenue as a connection to the Charles River, Cambridge staff expressed interest in changing the signed bicycle route so that it travels along Western Avenue instead of Magazine Street. Although the route would change, the original signs along Magazine Street would not be removed because they may still be helpful wayfinding tools for people traveling in the area. New southbound route signage should read “Charles River” instead of “BU Bridge,” which the signage currently indicates (Figure 3). Once each branch of the bicycle route reaches the Charles River, additional signage should direct users to locations such as the BU Bridge. Figure 4 illustrates the alternate southbound bicycle route along Western Avenue.

Figure 3
Southbound Bicycle Route BU Bridge Signage

Figure 3 – Image of the wayfinding signage for the southbound bicycle route that directs bicyclists from Cambridge to the BU Bridge. 

Replace Missing Wayfinding Signage

As MPO and Cambridge staff walked the signed bicycle route, there were a few locations where signage was not posted, but is needed. Wayfinding signs should be added to the following locations:

Improve Clarity of Turning Maneuvers

Heading north through Central Square, it is difficult for bicyclists to turn left onto Douglass Street from Massachusetts Avenue immediately after turning right onto Massachusetts Avenue from Brookline Street. Several ideas were proposed for remedying this concern:

Another improvement at Massachusetts Avenue and Douglass Street that was mentioned during the walk audit is the addition of a sign that would tell bicyclists traveling west along Massachusetts Avenue that they could turn right at Douglass Street to travel along the signed bicycle route to Inman Square.

A separate intersection along the route where bicycle and motorist conflicts could arise is the left turn from the Harvard Street bike lane to the contraflow bike lane on Norfolk Street. This road has a much lower traffic volume and slower travel speeds than Massachusetts Avenue, which means that collisions tend to be avoided. While this intersection might not require any changes, two ideas for improving the location are worth noting:

Improve Intersection Crossings

According to Cambridge staff, it is difficult for bicyclists to cross Broadway and Hampshire Street when traveling north up Norfolk Street. To remedy this, raised crossings, to increase driver awareness of the crossings, and slow vehicle speeds could be constructed, although it would be important to assess the impact of this traffic-calming strategy on vehicular traffic flow along both roadways.

Figure 4 – Map of an alternate southbound bicycle route from Inman Square to the Charles River that travels down Western Avenue.

3.2      Improving Prospect Street for Bicyclists

Constructing bicycle facilties on Prospect Street would directly close the Central Square bicycle network gap. To provide safe bicycling conditions along Prospect street, MPO staff assessed the feasibility of constructing bicycle lanes for both directions of travel. The current right-of-way on Prospect Street is too narrow to accommodate continuous bicycle lanes, so the left-turn lanes on Prospect Street at the signalized intersections would need to be removed. These left-turn lanes were originally added to Prospect Street to reduce the number of crashes on the roadway and, according to City of Cambridge staff, this approach has proven successful. The potential safety implications of removing left-turn lanes to add bike lanes to Prospect Street, coupled with the unknown travel impacts of the Inman Square and River Street reconstruction projects, has led MPO staff to recommend that Cambridge should not provide additional bicycle accommodations on Prospect Street until the reconstruction projects are complete and the idea can be studied once more with updated travel information. To inform this future study, MPO staff offer the following summary2 of their evaluation of removing the Prospect Street left-turn lanes:

Prospect Street

Prospect Street is a locally controlled, two-lane, two-way arterial roadway that connects Central Square to Inman Square. It intersects Massachusetts Avenue at Western Avenue and River Street in Central Square, and intersects Hampshire Street near Inman Square. Massachusetts Avenue and Hampshire Street currently have conventional bike lanes in place. Both of these intersections are signalized. Between Massachusetts Avenue and Hampshire Street, Prospect Street crosses three more signalized intersections at Bishop Allen Drive, Harvard Street, and Broadway. Exclusive left-turn lanes are present on Prospect Street at Bishop Allen Drive, Harvard Street, Broadway, and on the northbound leg of the Hampshire Street intersection.

Pedestrian and Bicycle Comfort

An evaluation of the current conditions of Prospect Street, as it relates to pedestrian levels of traffic stress (LTS) and bicycle levels of comfort (BLC), scores the roadway at an LTS 3 (LTS scale 1 to 4) and BLC 43 (BLC scale 1 to 5). This indicates that it presents a moderate-to-great amount of traffic stress and may be uncomfortable for many, or most, bicyclists. Prospect Street contains constant motor vehicle traffic, with no bike lane, and steady bus traffic—9.5 buses per hour, (4.75 buses per hour in each direction)—that makes frequent stops near the Bishop Allen Drive, Harvard Street, and Broadway intersections.


Staff examined crash records from the MassDOT Registry of Motor Vehicles from 2011 to 2013. There were 108 crashes reported in the segment of Prospect Street between Massachusetts Avenue and Hampshire Street. Of the total reported crashes, 16 involved bicycle crashes, with injuries resulting from 63 percent of the bicycle crashes. Of the 12 pedestrian crashes, 42 percent resulted in injuries, as did 19 percent of the 80 reported vehicle-only crashes. Half of the total number of injury crashes between 2011 and 2013 were bicycle- and pedestrian-related crashes.

The intersections along Prospect Street have crash rates somewhat higher than the state/district average of 0.70 crashes per million entering vehicles (MEV).4 The intersection crash rates per MEV for locations along Prospect Street are as follows.

Further, Cambridge staff noted that prior to installing the left-turn lanes at the signalized intersections along Prospect Street, there were a large number of crashes at this location because of turning vehicles. This led to installation of the present left-turn lanes on Prospect Street.

Existing Traffic Operations Conditions

To determine the effect of installing bike lanes in place of left-turn lanes, MPO staff built a traffic analysis network for the AM and PM peak periods with Synchro 9.5 The five signalized intersections along Prospect Street operate satisfactorily overall during the AM peak period (Level of Service [LOS] D or better), although some individual movements operate at LOS E or F. During the PM peak period, the northbound movements on Prospect Street operate at capacity (LOS E) at the intersections of Prospect Street at Massachusetts Avenue and at Bishop Allen Drive; these intersections as a whole operate at LOS E. The other three intersections operate satisfactorily during the PM peak period.

Proposed Improvement Alternatives and Evaluation

MPO staff developed and analyzed the impact of removing left-turn lanes and adding bicycle lanes on vehicular traffic operations for two alternative traffic signal optimization scenarios. The following are the two alternatives that were evaluated.  

The results of traffic operations analysis for the five Prospect Street intersections indicate that the intersections operated at LOS C or better. The 50th percentile queues do not exceed lane storage lengths. Queue lengths are expected to be equal to or less than the 50th percentile queues half of the time—95th percentile queues may exceed storage length; 95th percentile queues are met or exceeded 5 percent of the time.

As with Alternative 1, the results of traffic operations analysis for the six Prospect Street intersections indicates that the intersections operated at LOS C or better. The 50th percentile queues do not exceed lane storage lengths. Queue lengths are expected to be equal to or less than the 50th percentile queues half of the time—95th percentile queues may exceed storage length; 95th percentile queues are met or exceeded 5 percent of the time.

Examples of the existing and proposed cross-sections at the Prospect Street intersections are shown in Figures 7 and 8.

Summary of Prospect Street Bicycle Lanes

Based solely on the above analysis of existing traffic operations and development, Prospect Street could be a good candidate for bike lanes. The two alternatives would ameliorate the Central Square bicycle network gap while accommodating people that drive, walk, bicycle, and take the bus. Alternative 1 proposes bike lanes between Massachusetts Avenue and the existing bike lane on Prospect Street north of Broadway. Adding this bike lane would provide 1,800 feet of roadway with bicycle facilities, contributing to 2,300 feet of continuous bike lane on Prospect Street. In addition to the fixes in Alternative 1, Alternative 2 also proposes a bike lane in place of the northbound left-turn lane at Hampshire Street. Alternative 2 would add an additional 300 feet of bike lane for 2,600 feet of continuous bike lane on Prospect Street. LTS for people biking would improve, thus increasing the number of people who would feel comfortable biking on Prospect Street.

However, since this study was undertaken, conditions and priorities in Cambridge have changed. Inman Square reconstruction is set to begin in 2018, and there are planning efforts underway for River Street and Central Square. These efforts could have significant impacts on the operations of Prospect Street. In addition, based on Cambridge’s feedback on safety regarding the conditions prior to installing the left-turn lanes and the numerous bus routes that travel the length of Prospect Street, staff recommended not removing the left-turn lanes at this time. Cambridge values the safety improvements for all Prospect Street users achieved by adding left-turn lanes and considers them to be necessary for providing acceptable operations to all road users. In contrast, designating a route for bicyclists along Prospect Street would only address conditions for one travel mode, and the City already offers a safer and more comfortable alternative for cyclists along its signed bicycle route through Central Square. Although operationally the intersections could function acceptably for motor vehicle traffic, removing the turn lanes could potentially impact pedestrian and bicycle LOS at the intersections. New analysis of traffic and travel behavior along Prospect Street should occur once the planning efforts at Inman Square, River Street, and Central Square are complete.

Figure 5 – Map of Alternative 1, which proposes adding bike lanes to Prospect Street from Massachusetts Avenue to Broadway.

Figure 6 – Map of Alternative 2, which proposes adding bike lanes to Prospect Street from Massachusetts Avenue to Hampshire Street.

Figure 7 – Images showing cross sections of existing and proposed conditions for Alternatives 1 and 2 at Prospect Street and Massachusetts Avenue and at Prospect Street and Bishop Allen Drive.


Figure 8 – Images showing cross sections of existing and proposed conditions for Alternatives 1 and 2 at Prospect Street and Harvard Street and at Prospect Street and Broadway.

4          Conclusion and Next Steps

This study offers the City of Cambridge a fresh perspective on Prospect Street—a thoroughfare that is well used by drivers, pedestrians, bus riders, and bicyclists—and proposes alternatives for improvement. This study examined the potential to close the Central Square bicycle network gap. However, based on this evaluation, staff recommends that neither improvement alternative—add a bicycle lane, and remove left-turns lanes along Prospect Street—be implemented at this time. Staff recommends re-examining these improvement alternatives once Cambridge has completed its planning efforts at Inman Square, River Street, and Central Square.

In the meantime, staff recommends that improvements be made to the existing signed bicycle route that directs travel through Central Square to Inman Square. These improvements include adding shared lane markings to roadways along the route without allocated separate travel ways for bicyclists, such as bike lanes; creating an additional southbound branch of the signed bicycle route along Western Avenue, in addition to the Magazine Street route; adding wayfinding signage at identified locations; improving clarity for both bicyclists and motorists of turning maneuvers where the signed bicycle route changes from one street to another; and improving crossings at busy, unsignalized intersections.



1 Beth Isler, Bicycle Network Evaluation (Boston Region Metropolitan Planning Organization, May 2014).

2 For the full evaluation, see “Improving Prospect Street” in Appendix A.

3 For a full description of LTS and BLC relative to Prospect Street, see Appendix A2.1.

4 Massachusetts Department of Transportation, 2016, Intersection Crash Rates,

5 Trafficware Inc., Synchro Studio 9, Synchro plus SimTraffic, Sugar Land, Texas.