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For a bicycling network to attract the widest possible segment of the population, its most fundamental attribute should be low-stress connectivity, that is, providing routes between people’s origins and destinations that do not require cyclists to use links that exceed their tolerance for traffic stress, and that do not involve an undue level of detour. The objective of this study is to develop measures of low-stress connectivity that can be used to evaluate and guide bicycle network planning. We propose a set of criteria by which road segments can be classified into four levels of traffic stress (LTS). LTS 1 is suitable for children; LTS 2, based on Dutch bikeway design criteria, represents the traffic stress that most adults will tolerate; LTS 3 and 4 represent greater levels of stress.As a case study, every street in San Jose, California, was classified by LTS. Maps in which only bicycle-friendly links are displayed reveal a city divided into islands within which low-stress bicycling is possible, but separated from one another by barriers that can be crossed only by using high-stress links. Two points in the network are said to be connected at a given level of traffic stress if the subnetwork of links that do not exceed the specified level of stress connects them with a path whose length does not exceed a detour criterion (25% longer than the most direct path).For the network as a whole, we demonstrate two measures of connectivity that can be applied for a given level of traffic stress. One is “percent trips connected,” defined as the fraction of trips in the regional trip table that can be made without exceeding a specified level of stress and without excessive detour. This study used the home-to-work trip table, though in principle any trip table, including all trips, could be used. The second is “percent nodes connected,” a cruder measure that does not require a regional trip table, but measures the fraction of nodes in the street network (mostly street intersections) that are connected to each other.Because traffic analysis zones (TAZs) are too coarse a geographic unit for evaluating connectivity by bicycle, we also demonstrate a method of disaggregating the trip table from the TAZ level to census blocks. For any given TAZ, origins in the home-to-work trip table are allocated in proportion to population, while destinations are allocated based on land-use data. In the base case, the fraction of work trips up to six miles long that are connected at LTS 2 is 4.7%, providing a plausible explanation for the city’s low bicycling share. We show that this figure would almost triple if a proposed slate of improvements, totaling 32 miles in length but with strategically placed segments that provide low-stress connectivity across barriers, were implemented.Authors -
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Low Stress Bicycling and Network Connec6vity
Peter G. Furth, Northeastern University
Most of the Population has a Low Tolerance for Traffic Stress
Classifying the Population by Tolerance for Traffic Stress
Interested but Concerned (60%)
No Way, No How (33%)
Strong & Fearless < 1%
Enthused & Confident (7%)
Source: Roger Geller, City of Portland
Classifying Network Elements by Level of Traffic Stress (LTS)
LTS 1: for children LTS 2: for traffic intolerant
adult
LTS 3: for “Enthused & Confident”
LTS 4: highest stress
What Is the “Bicycle Network” to an Individual?
1. All the streets and paths where one may legally ride
2. Inventory of designated / improved bike facili6es
3. Set of preferred or suggested routes 4. The set of streets and paths that don’t exceed
his / her level of tolerance for traffic stress
San Jose (south central), Stress Level 1
Connec&vity : Can You Get from A to B without exceeding a specified level of traffic stress?
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Level of Traffic Stress 1 (LTS 1) Islands
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SJSU Rooted Tree LTS 2
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Level of Traffic Stress 2 (LTS 2) Islands
San Jose (south central), Stress Level 1
Connec&vity : Can You Get from A to B without exceeding a specified level of traffic stress? without undue detour?
Detour Criterion
Low-‐stress route should not be more than
25% longer than the shortest route
OR (for short trips)
0.33 mi longer than the shortest route
Criteria for Level of Traffic Stress
• Bicycle Level of Service (BLOS, 1997) – Black-‐box formula yields A-‐F ra6ng – Data hungry – Doesn’t model intersec6ons well
• Bicycle Compa6bility Index (BCI, 1996) • Bikeway design criteria in places that have succeeded in abrac6ng the mainstream popula6on
New Set of Criteria
• Segments • Intersec6on Approaches • Crossings
LTS 1: suitable for children LTS 2: acceptable to traffic
intolerant adult
LTS 3: OK for “enthused & Confident”
LTS 4: highest stress
Based on Dutch criteria
Weakest Link Principle of Aggrega6on
The stress of a route = stress of its most stressful link
• Different from summing or averaging
1 1 1 4 1 1
Segments Segment Type Level of Traffic Stress
Stand-‐alone paths LTS = 1
Segregated paths (sidepaths, cycle tracks)
LTS = 1
Bike lanes LTS can vary from 1 to 4
Mixed traffic LTS can vary from 1 to 4
Dutch Criteria (CROW 2007) Lane configura=on
Daily traffic (vehicles/day)
Street type and speed limit
Urban local street
Urban through street
Rural local road
Fast traffic road
30 km/h (19 mph)
50 km/h (31 mph)
60 km/h (37 mph)
70+ km/h (44+ mph)
Two-‐way traffic with no centerline
<2500 Mixed traffica Bike laneb or cycletrackc
Advisory bike laned
Cycle track or low-‐speed service road
2000–3000 bike laneb or cycle tracke
3000–5000
>4000 Bike lane or cycle track
Bike lane or cycle trackc
Two lanes (1+1) any Bike lane or cycle track
Bike lane or cycle trackc
Four lanes (2 + 2) or more
any (Does not exist)
Cycle track or low-‐speed service road
aFor designated bike routes, a bike lane or advisory bike lane is op6onal. bMay be an advisory bike lane on road sec6ons with no centerline. cCycle track is preferred if there is parking; cycle track is recommended for designated bike routes. dAlthough CROW (2007) gives “mixed traffic” for this cell, the default layout for roads in this category is to mark advisory bike lanes. eCycle track is preferred for designated bike routes.
LTS > 1 LTS > 2 LTS > 3 LTS > 4
Street width (thru lanes per direction)
1 (n.a.) 2 or more (n.a.)
Sum of bike lane and parking lane width
15 ft or more
14 or 14.5 fta
13.5 ft or less
(n.a.)
Speed limit or prevailing speed
25 mph or less
30 mph 35 mph 40 mph or more
Bike lane blockage rare (n.a.) frequent (n.a.)
Criteria for Bike Lanes Alongside a Parking Lane
Dimensions aggregate using Weakest Link logic
Criteria for Bike Lanes Not Alongside a Parking Lane
LTS > 1 LTS > 2 LTS > 3 LTS > 4
Street width (thru lanes per direction)
1 2, if directions are separated
by a raised median
more than 2, or 2 without a
separating median
(n.a.)
Bike lane width 6 ft or more
5.5 ft or less (n.a.) (n.a.)
Speed limit or prevailing speed
30 mph or less
(n.a.) 35 mph 40 mph or more
Bike lane blockage rare (n.a.) frequent (n.a.)
Criteria for Mixed Traffic
Street Width Speed Limit 2-3 lanes 4-5 lanes 6+ lanes
Up to 25 mph LTS 1 a or 2 a LTS 3 LTS 4
30 mph LTS 2 a or 3 a LTS 4 LTS 4
35+ mph LTS 4 LTS 4 LTS 4
a. Use lower value for streets without marked centerlines or classified as residential and with fewer than 3 lanes; use higher value otherwise.
Traffic Stress on Intersec6on Approaches – “Pocket Bike Lanes”
Dutch criteria • RT lane must be short
• RT lane must begin abruptly
• Bike lane must con6nue straight
• Wide bike lane • Intersec6on angle keeps turning speed to 15 km/h
Criteria for Pocket Bike Lanes
Configuration Level of
Traffic Stress Single RT lane up to 150 ft long, starting abruptly while the bike lane continues straight; intersection angle such that turning speed is < 15 mph.
LTS > 2
Single RT lane longer than 150 ft ,starting abruptly while the bike lane continues straight; intersection angle such that turning speed is < 20 mph.
LTS > 3
Single RT lane in which the bike lane shifts to the left, but intersection angle and curb radius are such that turning speed is < 15 mph.
LTS > 3
Single RT lane with any other configuration; dual RT lanes; or RT lane plus option (through-right) lane
LTS = 4
Increased Traffic Stress on Widened Approaches
Added turn lanes (Monroe @ Stevens Creek)
Widened Intersec6on Approaches Interrupt Low-‐Stress Paths
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Stress at Crossings – Apparent Safe Routes Crossing Winchester Avenue
Stress at Crossings
Criteria for Crossings NO MEDIAN REFUGE Width of Street Being Crossed
Speed Limit Up to 3 lanes 4 - 5 lanes 6+ lanes Up to 25 mph LTS 1 LTS 2 LTS 4 30 mph LTS 1 LTS 2 LTS 4 35 mph LTS 2 LTS 3 LTS 4 40+ LTS 3 LTS 4 LTS 4
WITH MEDIAN REFUGE Width of street being crossed
Speed Limit Up to 3 lanes 4 - 5 lanes 6+ lanes Up to 25 mph LTS 1 LTS 1 LTS 2 30 mph LTS 1 LTS 2 LTS 3 35 mph LTS 2 LTS 3 LTS 4 40+ LTS 3 LTS 4 LTS 4
ADEC CalGIS 2012 Sacramento, CA 26
With Crossing Effect – Winchester becomes a barrier without any low-‐stress crossing
ADEC CalGIS 2012 Sacramento, CA 27
San Jose Street Network Stress Classifica6on
Distribu6on of Segment Miles by Level of Traffic Stress
Stress Level Miles Miles (percent) Lowest 1 2131 64%
Low 2 115 3% Medium 3 276 8%
High 4 678 20% Prohibited 5 134 4%
Total 3334 100%
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San Jose Street Network Stress Level 1
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San Jose Street Network Stress Level 2
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San Jose Street Network Stress Level 3
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San Jose Street Network Stress Level 4
Barriers
• Natural (rivers, mountains), RR, Freeways: Crossings collect traffic, tend to be high stress
• Freeways: Added stress from on-‐off ramps • Arterials lacking low-‐stress approaches with low-‐stress crossings
• Parks and Campuses (!) • Incomplete street grid, forcing traffic to use arterials
Incomplete Street Grid as Barrier
Permeable Barriers Can Be a Key to Connec6vity and Low Stress
Downing Ave – Wesnield Ave @ Hwy 17
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Level of Traffic Stress 2 (LTS 2) Islands
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Slate of Possible Improvements
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Resul6ng Network for LTS < 2
A Measure of Connec.vity
Percent Trips Connected, by Level of Traffic Stress
• Trip Table for Home-‐to-‐Work Trips Number of people traveling from zone i to zone j Which zone pairs are connected at a given LTS? TAZ (traffic analysis zone) = standard geographic unit
TAZ can be too coarse a geographic unit to model bicycle access
Disaggrega6ng Demand from TAZs to Blocks
• Origins: in propor6on to block popula6on • Des6na6ons: in propor6on to trip genera6on factors
Linking Block Centroids to the Network
Block centroid, with connectors to surrounding ver6ces
Home-‐Work Trip Connec6vity Trip Length < 4 mi < 6 mi < 8 mi All
LTS 1 0.7% 0.4% 0.3% 0.2% LTS 2 7.7% 4.7% 3.4% 2.2% LTS 3 22.6% 16.4% 13.2% 8.9% LTS 4 100.0% 100.0% 100.0% 100.0% Total trips 78,673 136,652 189,439 292,396
Trip Length < 4 mi < 6 mi < 8 mi All LTS 1 1.7% 1.0% 0.8% 0.5% LTS 2 14.9% 12.7% 11.1% 7.9% LTS 3 27.4% 22.7% 20.0% 14.6% LTS 4 100.0% 100.0% 100.0% 100.0% Total trips 78,673 136,652 189,439 292,396
Before AOer
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Acknowledgement
• Co-‐researcher Maaza Mekuria, PhD, Axum Engineering & Design
• Support from the Mineta Transporta6on Ins6tute
• Inspira6on from Rails to Trails Conservancy
