CAMBRIDGE SHARED STREETS

CAMBRIDGE SHARED STREETS

STREETS

Snow Removal and Stormwater Management

In Cambridge, property owners are responsible for removing snow from sidewalks, while the vity removes snow from the street. After conversion to a shared street, these delineations proved less stark. In Harvard Square, property owners have proactively shouldered additional snow removal responsibilities. Stormwater management has also been a consideration, because removing

a curb changes runoff flows. To prevent puddling near buildings, shared streets in Cambridge grade toward a small gully in the center of the road.

Street Design Elements

33 Lane Width

The elements that make up city streets, from sidewalks to

37 Sidewalks

38 Sidewalk Zones

travel lanes to transit stops, all vie for space within a limited

40 Sidewalk Design

right-of-way. Transportation planners and engineers can

45 Curb Extensions

use this toolbox to optimize the benefits the community

47 Gateway

receives from its streets.

48 Pinchpoint

49 Chicane

50 Bus Bulbs

51 Vertical Speed Control Elements

53 Speed Hump

54 Speed Table

55 Speed Cushion

57 Transit Streets

58 Dedicated Curbside/ Offset Bus Lanes

60 Dedicated Median Bus Lanes

61 Contra-Flow Bus Lanes

62 Bus Stops

65 Stormwater Management

67 Bioswales

68 Flow-Through Planters

69 Pervious Strips

70 Pervious Pavement

Lane Width The width allocated to lanes for motorists, buses, trucks,

bikes, and parked cars is a sensitive and crucial aspect of street design. Lane widths should be considered within the assemblage of a given street delineating space to serve all needs, including travel lanes, safety islands, bike lanes, and sidewalks. Each lane width discussion should be informed by an understanding of the goals for traffic calming as well as making adequate space for larger vehicles, such as trucks and buses.

Travel lanes are striped to define

RECOMMENDED the intended path of travel for

DISCUSSION

vehicles along a corridor. Histor-

The relationship between lane widths

Lanes greater than 11 feet should not

ically, wider travel lanes (11–13 feet)

and vehicle speed is complicated by

be used as they may cause unintended

have been favored to create a more

many factors, including time of day,

speeding and assume valuable right-of

forgiving buffer to drivers, especially

the amount of traffic present, and

-way at the expense of other modes.

in high-speed environments where

even the age of the driver. Narrower

narrow lanes may feel uncom-

streets help promote slower driving

Restrictive policies that favor the use

fortable or increase potential for

speeds. which in turn reduce the

of wider travel lanes have no place

side-swipe collisions.

severity of crashes. Narrower streets

in constrained urban settings, where

Lane widths less than 12 feet have

have other benefits as well, including

every foot counts. Research has

also historically been assumed to

reduced crossing distances, shorter

shown that narrower lane widths can

decrease traffic flow and capacity,

signal cycles, less stormwater, and less

effectively manage speeds without

a claim new research refutes. 1 construction material to build.

decreasing safety and that wider lanes do not correlate to safer streets. 3

Lane widths of 10 feet are appropriate

Moreover, wider travel lanes also

in urban areas and have a positive

increase exposure and crossing

impact on a street’s safety without

distance for pedestrians at inter-

impacting traffic operations. For

sections and midblock crossings. 4

designated truck or transit routes, one travel lane of 11 feet may be used

Use striping to channelize traffic,

in each direction. In select cases,

demarcate the road for other uses, and

narrower travel lanes (9–9.5 feet)

minimize lane width.

can be effective as through lanes in conjunction with a turn lane. 2

SAN FRANCISCO, CA

Striping should be used to delineate parking and curbside uses from the travel lane.

2-way streets with low or medium within the overall assemblage

1 Lane width should be considered

OPTIONAL

volumes of traffic may benefit from the of the street. Travel lane widths of

2 Parking lane widths of 7–9 feet

use of a dashed center line with narrow

lane widths or no center line at all. safety in urban settings while discour-

10 feet generally provide adequate

are generally recommended.

In such instances, a city may be able aging speeding. Cities may choose to

Cities are encouraged to demarcate

to allocate additional right-of-way use 11-foot lanes on designated truck

the parking lane to indicate to drivers

to bicyclists or pedestrians, while and bus routes (one 11-foot lane per

how close they are to parked cars. In

permitting motorists to cross the direction) or adjacent to lanes in the

certain cases, especially where loading

center of the roadway when passing. opposing direction.

and double parking are present, wide

parking lanes (up to 15 feet) may be used. Wide parking lanes can serve

Additional lane width may also be

multiple functions, including as indus-

necessary for receiving lanes at turning

trial loading zones or as an interim

locations with tight curves, as vehicles

space for bicyclists.

take up more horizontal space at a curve than a straightaway.

3 For multilane roadways where transit or freight vehicles are

Wide lanes and offsets to medians are

present and require a wider travel lane,

not required but may be beneficial and

the wider lane should be the outside

necessary from a safety point of view.

lane (curbside or next to parking). Inside lanes should continue to be

designed at the minimum possible width. Major truck or transit routes through urban areas may require the use of wider lane widths.

ELMORE , OH

S T R E E T D E SI G N E L E M E N T S

Wider travel lanes are correlated with higher vehicle speeds.

Average Lane Width (feet converted from meters)

13'2" 13'11"

52.8 km/hr 49.7 d from

rt e 46.6 nve o

h p c 43.5 m

d e ( e p 40.4 S

37.3

Percentile 34.2 th 5

8 31.1

“As the width of the lane increased,

Regression Line

the speed on the roadway increased... When lane widths are 1 m (3.3 ft) greater,

85th Percentile

speeds are predicted to be 15 km/h

Speed of Traffic

(9.4 mph) faster.” Chart source: Fitzpatrick, Kay, Paul Carlson, Marcus

Brewer, and Mark Wooldridge. 2000. “Design Factors That Affect Driver Speed on Suburban Streets.” Transportation Research Record 1751: 18–25.

Sidewalks

Sidewalks play a vital role in city life. As conduits for pedestrian movement and access, they enhance connectivity and promote walking. As public spaces, sidewalks serve as the front steps to the city, activating streets socially and economically. Safe, accessible, and well-maintained sidewalks are a fundamental and necessary investment for cities, and have been found to enhance general public health and maximize social capital. Just as roadway expansions and improvements have historically enhanced travel for motorists, superior sidewalk design can encourage walking by making it more attractive.

S T R E E T D E SI G N E L E M E N T S

Sidewalk Zones

Prevailing design guidelines recommend a minimum sidewalk cross-section of 5 feet, exclusive of other amenities and large enough for two people walking side by side. While this dimension meets minimum ADA accessibility stan- dards, many cities have chosen to adopt wider standards. Sidewalk standards should accommodate higher anticipated pedestrian volumes and provide ample space for an expanded frontage zone as well as other street furniture, such as trash receptacles, bus stops,

signage, and bike share stations. 1

Frontage Zone

Pedestrian Through Zone

FRONTAGE ZONE

PEDESTRIAN 1 2