[sustran] Bicycles - Congestion Impacts

[Todd Litman]

At 11:08 AM 4/17/98 -0400, Eric Bruun wrote:
>
>I think the space efficiency of bicycles you quoted, at 
>only twice as good per lane mile as an auto, is not correct.
>Bicycles do not need the lane width, nor do they have to 
>travel single file, rather they can move in formation
>like a squadron of fighter aircraft.

Here is the analysis of bicycles' congestion impacts from "Quantifying
Bicycling Benefits for Achieving Transportation Demand Management Goals,"
available from our institute.


A.	Congestion
Traffic congestion costs include increased travel time, vehicle operating
costs, stress and air pollution. The potential congestion reduction and
travel time savings resulting from a shift from Single Occupant Vehicle
(SOV) travel to bicycling depends on specific circumstances. To analyze
bicycle congestion impacts, traffic conditions are divided into four classes:

1.	Uncongested roads or separated paths.   
Bicycling on uncongested roads causes no traffic congestion. 

2.	Congested roads with space for bicyclists.
Bicycling on the road shoulder (common on highways); the curb lane (common
in suburban areas and newer urban streets); or a designated bike lane
contributes little to traffic congestion except at intersections and
driveways where other vehicles' turning and lane shifting maneuvers may be
delayed. Table 1 summarizes congestion impacts of bicycling by road width,
although traffic volume and intersection design are also factors. 

Table 1	Passenger-Car Equivalents for Bicycles by Lane Width 
				< 11 ft. Lane		11-14 ft. Lane	> 14 ft. Lane
				------------		--------------	-------------
	Riding With Traffic		1.0		0.2			0.0
	Riding Against Traffic	1.2		0.5			0.0

(Policy on Geometric Design for Streets and Highways, AASHTO (Washington
DC), 1990.)


3.	Narrow, congested roads with low speed traffic.
Bicycling on a narrow, congested road when the rider can safely keep up
with traffic (common in urban traffic averaging 15 mph or less) probably
contributes slightly less to congestion than an average car, due to a
bicycle's smaller size.

4.	Narrow, congested roads with moderate to high speed traffic.
Bicycling on a narrow, congested road when the rider is unable to keep up
with traffic can contribute to traffic congestion, depending on how easily
faster vehicles can pass.  

Congestion is reduced when automobile drivers shift to bicycling under the
first three condition. Only under condition #4 would a shift from driving
to bicycling fail to reduce congestion. This probably represents a minor
portion of bicycle transport mileage because most bicyclists avoid riding
under such conditions, and bicycling is forbidden on urban freeways where
congestion costs are usually highest. 



Sincerely,

Todd Litman, Director
Victoria Transport Policy Institute
"Efficiency - Equity - Clarity"
1250 Rudlin Street
Victoria, BC, V8V 3R7, Canada
Phone & Fax: 250-360-1560
E-mail:      litman at islandnet.com
Website:     www.islandnet.com/~litman