Report by Paul Smith, AICP

Vassar Streetscape Project Bicycle Facility Design

Paul B. Smith, AICP

May 2002

Introduction

This paper describes the bicycle facilities included as part of the Vassar Streetscape design project.

The design includes separate-lying one-way cycle tracks transitioning to one-way bicycle lanes at intersections.

The cycle tracks and bicycle lanes are designed for the exclusive use of bicycles and will be so designated by signing and pavement markings.

The one-way cycle track design is based on design guidelines published by the Centre for Research Standardization in Civil Engineering - The Netherlands (CROW) and the Road Directorate of Denmark.

The design also conforms to design guidance published by the American Association of State Highway and Transportation Officials (AASHTO)]

The bicycle lane design as proposed at the Massachusetts Avenue and Main Street intersections conforms to AASHTO design guidelines as well as European design guidelines.

The greatest conflicts on bicycle paths or cycle tracks are at intersections. Vassar Street is unusual for a city street in that there is only one intersection (Massachusetts Avenue) in the one-mile long project area.

The potential for conflicts have [sic] been minimized by transitioning the cycle tracks to bicycle lanes at this intersection. The cycle tracks also transition to on-street bicycle facilities at both ends (Main Street and Audrey Street).

The Vassar Streetscape design as proposed is responsive to the needs of the majority of cyclists and recognizes the improved safety afforded by the transition to bicycle lanes at street intersections.

We believe this design fits the special conditions of Vassar Street, which are not typical of Cambridge. It is not meant to imply that the design would be appropriate throughout the city, where conditions are different.

Bicycle lane design

One-way bicycle lanes will be provided on Vassar Street at the Massachusetts Avenue and Main Street intersections (see figures 1 a, 1 b and 2). The bicycle lanes will be five feet wide and adjacent to the curb. Cyclists will travel in the same direction as vehicles in the adjacent travel lane, i.e., with the flow of traffic.

At both the Massachusetts Avenue and Main Street intersections, an additional travel lane will be provided on Vassar Street:

•    On both approaches to Massachusetts Avenue, a separate left-turn only lane and through/right lane will be provided. The bicycle lane remains against the curb on these approaches. Vehicles turning right onto Massachusetts Avenue must yield to through cyclists, just as they would on a street with only one approach lane. The position of the bicycle lane is consistent with AASHTO design guidance.

•    On the Vassar Street approach to Main Street, two approach lanes are provided on Vassar Street - a left/through lane and a right/through lane. In this instance, the bicycle lane also remains against the curb. Vehicles turning right onto Main Street must yield to through cyclists, just as they would on a street with only one approach lane. The position of the bicycle lane is consistent with AASHTO design guidance.

Cycle track design

Between intersections, cyclists will travel on one-way cycle tracks located on each side of Vassar Street. The cycle track will be five feet wide with a two-foot shoulder/clear zone on the left side and a flush separator to the right adjacent to the sidewalk (see figures 3 and 4). The cycle track will be at the same elevation as the tree strip to the left and the sidewalk to the right. It will be a different material and color than the sidewalk. The entire area of tree strip, cycle track and sidewalk is raised above street level.

Cyclists would operate on the cycle track in a similar manner to how they operate in a bicycle lane on the street.

Sign up for the bike: Design manual for a cycle friendly infrastructure (CROW, 1993) states that the preferred effective width of a one-way cycle track with a peak-hour volume in one direction of up to 150 bicycles is 1.50 meters (4.92 feet). The current design includes a 5-foot wide cycle track, a 1-ft wide paved shoulder on the left side of the cycle track and an area about 1-ft wide to the left of the shoulder that is also rideable. Thus, the total width of the cycle track and the rideable area to the left before the tree trunk is approximately 7 feet (2.13 m). According to CROW, "the rule of thumb for comfortable side-by-side cycling can be taken as: 1.00 m per cyclist." This means that cyclists on the Vassar Street cycle track have the possibility of passing or overtaking maneuvers, if necessary, without going into the walkway. In addition, a 12 inch wide separator will be placed between the cycle track and the sidewalk. This separator will be rideable.

Several facets of bicycle operations on the cycle track are different than on-street operations. Each of these operational issues is explained as follows.

Separation from pedestrians

Signing, pavement markings and education will be used to inform bicyclists and pedestrians of their respective operating spaces, as is done for similar facilities in Europe. As described previously, there is over seven feet of rideable space on the cycle track and shoulders entirely separate from the sidewalk.

All signs and light standards will be located in the five-foot wide tree strip or verge.

For the most part, the sidewalk is eight feet wide and is also free of obstructions. The combined lateral distance for the separate bicycle and pedestrian facilities is 15 feet. We believe this is sufficient space to safely, accommodate both cyclists and pedestrians.

While the bicycle facility is above street grade at the same level as the sidewalk, it is not a "sidewalk bikeway". A "sidewalk bikeway" is a segment of sidewalk designated as part of a bicycle route. The standard design for a sidewalk (4 to 5 foot width with a 6" curb separating it from the street) cannot reasonably accommodate bicycle traffic and pedestrians. Studies have demonstrated that routing bicycles onto a typical sidewalk increases the likelihood of crashes between bicycles and pedestrians. Accident data related to sidewalk bikeways is not applicable to the Vassar Street facility. The Vassar Streetscape design proposes separate facilities for bicycles and pedestrians each of which meets the operational needs of the respective users.

One-way cycle tracks are used extensively in Europe and continue to be recommended in recent design manuals published in Denmark and the Netherlands.

MIT has the opportunity and has made the commitment to educate students, faculty and staff on proper operation on the one-way cycle tracks and lanes.

Signing and pavement markings will be provided to designate proper use of the bicycle facilities.

Bicycle parking facilities within the MIT campus will be placed in locations that are not only convenient to building entrances, but also easily accessible to driveways and mid-block pedestrian/bicycle crossings that provide ramped access to the cycle facilities on each side of the street.

Driveway junctions

The design team has taken measures to raise motorists' awareness of the presence of cyclists where the one-way cycle tracks intersect driveways. A typical cycle track/driveway junction is shown in figure 5. At these junctions, cyclists will have the right of way.

The driveway will rise to meet the elevation of the cycle track. Based on City guidelines, this will be a steep incline, where motorists must slow down. Motorists are required to yield to cyclists just as they yield to pedestrians at sidewalk/driveway junctions.

The steep ramp from the street onto the driveway will force motorists to slow down significantly when turning from Vassar Street onto a driveway. The placement of on-street parking on the north side of Vassar Street and trees on both sides of Vassar Street is being designed so as not to restrict motorists' visibility of cyclists when motorists are turning into a driveway.

Most of the driveways are lightly used. The bicycle facility will cross the busiest driveway at the Stata Center as a bicycle lane and will be painted blue to alert motorists to the presence of bicycles.

Mid-block crosswalks

Several mid-block crosswalks are provided on Vassar Street in the project area. Some will be new and others are existing crosswalks that will be redesigned. Bicycle crossing areas will be provided on both sides of the mid-block crosswalks to allow bicycle movements between the cycle tracks on each side of the street (see figure 6).

Transitions

Transitions have been designed between the bicycle lanes and cycle tracks at intersections. In most cases the cyclist simply continues straight (see figure 7). In other cases a gentle curve in the cyclist's path is required (see figure 8). The transitions are described below for eastbound and westbound cyclists:

Westbound

•    Beginning at Main Street, cyclists travel westbound in a bicycle lane between the curb and a wide travel lane. Then the bicycle lane ramps up and straight onto a cycle track. The tree strip begins at this point to the left of the cycle track.

•    Approaching Massachusetts Avenue, the cycle track ramps down and straight onto a bicycle lane. The first 75 feet of the bicycle lane is painted blue to alert motorists to bicyclists in this transition zone.

•    The bicycle lane continues on the far side of the Massachusetts Avenue intersection and then ramps up and straight onto the cycle track.

•    At the western end of the project, the cycle track will curve slightly to the left and into a short section of bicycle lane on the approach to Audrey Street. This short section of bicycle lane will also be painted blue to alert motorists to bicyclists in this transition zone.

Eastbound

•    Beginning at Audrey Street, cyclists travel eastbound in a bicycle lane adjacent to the curb. Then the bicycle lane turns slightly to the right and ramps up onto a cycle track. The tree strip begins at this point to the left of the cycle track.

•    Approaching Massachusetts Avenue, the cycle track turns slightly to the left and ramps down onto a bicycle lane. The first 90 feet of the bicycle lane is painted blue to alert motorists to bicyclists in this transition zone.

•    The bicycle lane continues on the far side of the Massachusetts Avenue intersection and then turns slightly to the right and ramps up onto a cycle track.

•    At the eastern end of the project, the cycle track will curve slightly to the left and ramp down onto a bicycle lane. The first 100 feet of the bicycle lane is painted blue to alert motorists to bicyclists in this transition zone.

Pavement Design Features

The pavement system used in the Vassar Streetscape project has been designed to avoid problems that can be caused by tree roots interfering with pavements in cycle tracks, in particular heaving and cracking caused in the pavement surface by shallow tree roots. The causes of these problems are simple, and the solutions are equally simple and direct. Tree roots can quickly become confined in a traditional tree pit, which offers no escape from the area immediately surrounding the tree to other areas where they can take up water and nutrients. Root growth often becomes aggressive, seeking out any available pathway to reach new sources for the nourishment of the tree. As most soils under pavements are placed at a high compaction to prevent settlement, roots cannot force their way through. Often, roots find a layer immediately beneath the pavement where they can penetrate, by pushing the pavement up. As the size of the root increases, the "heave" in the sidewalk also increases. Where rigid pavements (such as concrete) are used, roots can lift and eventually crack the entire pavement section. Flexible pavements (such as bituminous concrete) lift only immediately above the root, and eventually "tear" the pavement.

The solution is to provide a medium underneath the pavement surfaces that will allow roots to pass through without losing the structural capacity of the soil. The Vassar Streetscape project includes a "treeway" system beneath the tree strip and the bicycle path. The treeway consists of a soil that is a blend of a coarse mineral soil (which provides the structural capacity) and organic matter. The mineral soil creates a series of voids in its matrix which are filled with the organic matter; roots are then able to infiltrate through the voids and access nutrients and water stored in the organic matter. As the voids are already created in the matrix, the roots do not displace any soil, and thereby do not create reflective cracking, heaving or tearing of the surface. Also, scientific studies indicate that roots tend to grow at the lower levels of such a matrix (in the case of Vassar Street, the matrix is approximately two feet thick), further isolating the surface from impacts of root growth.

Snow removal from the combined sidewalk/cycle track area should be significantly improved since the combined width of the surface (over ten feet wide) will allow the use of larger, more efficient equipment.

Conclusion

The streetscape project will include new and separate facilities for the exclusive use of bicycles.

Currently bicycles operate in the street in shared travel lanes with motor vehicles.

The new design includes one-way cycle tracks, which separate cyclists from motor vehicles along sections of the street between intersections.

At intersections, the bicycle facility transitions onto the street as bicycle lanes. While a variety of different design solutions are available for any project, MIT and the City have chosen to try a different solution on a unique section of Vassar Street through the center of the MIT campus. We believe that this design is appropriate for cyclists who will travel along Vassar Street.

[Table of Contents]
[Previous: Comments on letter from planner]
[Next: Comments on Paul Smith report]