I was encouraged by some of you to review past ITE articles about how

all-way stop signs affect speed, accidents, and disrespect for stop

signs in general -- topics on which there seems to be a measure of urban

legend. For those who are interested, here's the 3-part summary.

1) DO ALL-WAY STOPS INCREASE ACCIDENTS? There are 3 studies with

accident data; 1 is urban, two are rural. All of them found that all-way

stops (compared to 2-way stops) decreased accident rates, except on

arterials with more than 10,000 ADT where a significant increase was

observed.

2) DO ALL-WAY STOPS SLOW TRAFFIC OR SPEED UP TRAFFIC? The two studies on

speed showed what you'd expect:  that stop signs slow drivers at the

intersections, but that the effect lasts only for about 200 ft. One

study looked at speed 500 ft from the intersection, and found that stop

signs had no significant impact on speed. That study that is wrongly

cited in another of the ITE papers as showing that stop signs increase

speed between intersections.

3) DO UNWARRANTED ALL-WAY STOPS ENCOURAGE DISRESPECT FOR STOP SIGNS IN

GENERAL? The one study that examined this, by comparing driver behavior

at nearby existing stop signs before & after some all-way stops were

installed, found no support for this idea.

Here are titles, abstracts, and my comments.

*Stop sign warrants: Time for change

<http://www.ite.org/logon.asp?destination=/membersonly/itejournal/pdf/JJA92A25.pdf>*

*/LaPlante, John N. ; Kropidlowski, Chester R./*

Experiences are related and the recommendation is made that the Manual

on Uniform Traffic Control Devices and the various state counterparts

should be revised to indicate that the usual stop sign warrants do not

apply to local residential streets in dense urban areas, or at least to

give more credence to limited sight distances on low-speed local

roadways. It is also noted that the accident warrants are much too high

for low-volume roads, where stop sign installations can make a positive

traffic safety difference, even though the results can only be detected

when a significant number of individual intersections are aggregated

into logical groupings.

/*Date: *10/1992 vol. 62, no. 10/

This paper, using Chicago data, finds a substantial accident reduction

with both 2-way stops (where there had been no signs previously) and

with 4-way stops, except when stop signs are put on a street with more

than 10,000 ADT, where all-way stop signs tend to raise the accident

rate. By comparing nearby intersections that had stop signs before, it

found no support to the idea that unwarranted stop signs in one place

encourage disrespect for stop signs at other places.

*4-Way Stop Signs Cut Accident Rate 58% at Rural Intersections

<http://www.ite.org/logon.asp?destination=/membersonly/itejournal/pdf/JKA84A23.pdf>*

*/Reprinted from Better Roads /*

Accident rates declined by an average of 50 percent at 10 rural Michigan

intersections following a replacement of two-way stop signs with

4fourway stop signs. This article reports the results of a study which

compared data for each of these intersections prior to and following the

switch to four-way stop signs. The data included: accident experience

(accident rates and costs), vehicle operating costs, travel time, fuel

consumption, and vehicle emissions.

/*Date: *11/1984 vol.54, no.11/

*An Evaluation of 4-Way Stop Sign Control

<http://www.ite.org/logon.asp?destination=/membersonly/itejournal/pdf/JHA82A16.pdf>*

*/Briglia, Peter M., Jr. /*

The Michigan Department of Transportation installed four-way stop signs

at low volume, high speed, rural intersections in an effort to remedy

the persistent night-angle accident pattern occurring at these

intersections. This article reports the results of a performance

comparison study of these installations with the two-way stops they

replaced. Factors evaluated include accident experience, motor vehicle

operating costs, travel time, fuel consumption, and air quality impacts.

/*Date: *8/1982 vol.52, no.8/

This study found a 66% reduction in total accidents and a 93% reduction

in fatal accidents. (Rural context.)

*Controlling speeds on residential streets

<http://www.ite.org/logon.asp?destination=/membersonly/itejournal/pdf/JDA89A37.pdf>*

*/Beaubien, Richard F. /*

This article describes the experiences of Troy, Michigan in dealing with

complaints of speeding on residential streets over the past decade.

Comparisons of 1975 speed study and observance study results with 1985

and 1986 results at the same locations are included. The nature of the

problem is described, and the ineffectiveness of stop signs is noted. It

is noted that the neighborhood itself must take some responsibility for

the solution. A majority of the violations are by residents of the

neighborhood. Residents can address the problem by increasing the

awareness of the problem in the neighborhood, and by assisting the

police. Troy has a committee of citizens appointed to advise the City

Council on proposed traffic regulations. This citizen involvement is

important because it allows objectivity before a political decision is

made.

/*Date: *4/1989 vol. 59, no. 4/

This article found that speed measured 500 ft away from the intersection

didn't change significantly when a stop sign was installed. No accident

data.

*Multi-Way Stop Signs - Have We Gone Too Far?

<http://www.ite.org/logon.asp?destination=/membersonly/itejournal/pdf/JEA83A19.pdf>*

*/Chadda, Himmat S. ; Carter, Everett C./*

This paper encourages the rational and judicious use of multi-way stop

signs in conformance with the warrants presented in the Manual on

Uniform Traffic Control Devices (MUTCD). Various other reasons that have

been used for installing multi-way stop signs are discussed, and the

problems/impacts of unwarranted stop signs are briefly summarized.

Examples, based on discussions between the authors and city and state

officials, of cities with experience in removal of unnecessary stop

signs are described. In conclusion the authors give suggested steps for

identifying unwarranted stop control and for providing data for

decisions on subsequent removal.

/*Date: *5/1983 vol.53, no.5/

No new data in this article; rather, descriptions of programs cities

have to eliminate unwarranted all-way stops. This article wrongly cites

the previous article (Beaubien) as giving evidence that unwarranted

all-way stops increase speeds.

*Speed Control Measures in Residential Areas

<http://www.ite.org/logon.asp?destination=/membersonly/itejournal/pdf/JCA77A28.pdf>*

*/Marconi, William /*

The effectiveness of some regulatory and channelization measures to

achieve speed reductions was evaluated using the 95th percentile speed

as the parameter for comparison, stop signs were found to be the most

effective device to reduce speeds, with the top speeds recorded being 10

mph. Traffic circles are the next most effective with top speeds ranging

from 16 to 22 mph, more than twice the speeds at stop sign locations.

Rumble strips are the third most effective with top speeds ranging at

different locations from 17 to 35 mph. Street narrowings were almost

totally ineffective. The area of influence of a stop sign in terms of

speed reduction was about 100 to 200 feet on either side of the device.

Approaching a traffic circle, motorists start deceleration later. The

speeds of motorists leaving a traffic circle do not equal those of

motorists leaving a stop sign until they are about 150 feet past the

intersection.

/*Date: *3/1977 vol.47, no.3/

He finds that stop signs lower speeds greatly if speed is measured just

before the intersection. He finds that the lower speed effect lasts for

only about 200 ft. Another interesting finding was nearly no effect on

speed from narrowing several streets. However, in the commentary, he

notes that after narrowing, lane widths were still 11 ft or greater, and

suggests that if they'd gone down to 7 to 9 ft (sic), they might have

seen some real speed reduction.

--

Peter G. Furth <pfurth@coe.neu.edu>

Professor, Department of Civil & Environmental Engineering

Northeastern University, room 400 SN

Boston, MA 02115

617.373.2447 voice; 617.373.4419 fax