Why Traffic Slows at Tunnel Approaches

Via ENR, an interesting piece on tunnels, shockwaves, and traffic psychology.

“If everybody goes the same speed and distance and nobody uses the brakes, you can through-put more vehicles,” Khattak said.

These tunnel-driving behaviors are so notorious that the proposal for the group interested in widening the HRBT suggests making the tunnel four lanes in each direction and the approaches only three lanes.

Scerbo noted, though, that regardless of how many lanes are added at the tunnels, many drivers will still brake.

Although some of these driver reactions can’t be controlled, the physical environment they’re reacting to can.

“We’ve tried to counter this whole perception that you’re driving into a hole in the water… so you don’t feel like you’re going into a different environment than you’re coming from,” said Dwayne Cook, regional operations manager for the Virginia Department of Transportation.

This entry was posted on Wednesday, November 10th, 2010 at 11:40 am and is filed under Traffic Engineering, Traffic Psychology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

14 Responses to “Why Traffic Slows at Tunnel Approaches”

  1. Stephanie Says:

    It’s dark and that’s scary on an instinctive level.

  2. Cap'n Transit Says:

    Allow me to point out that this is nowhere near as much of a problem with trains, where you’ve got one professional driver on a cleared block for hundreds of passengers.

  3. mulad Says:

    It’s an interesting problem, and I think we see shades of it whenever there’s a sunken freeway. The barrier of earth off to the side makes people more nervous as it gets closer to the roadway — A tunnel simply completes the enclosure and makes the space feel even more confining.

    There must be a few more things that could be tried — perhaps make the individual lanes wider or paint the ceiling blue to look more like sky.

    Unfortunately, I suspect that an effort to train people to just ignore the feeling of danger would ultimately backfire — if we take that feeling away, I’d worry about reducing the effectiveness of traffic-calming efforts elsewhere.

    I’m not familiar with these tunnels or the future project, but would additional buses help with the problem? If you can get people to take transit or carpool, that could reduce the number of vehicles that could trigger a backup.

  4. Betty Barcode Says:

    People slow down for all the right reasons, such as the recognition that an accident in a tunnel would be deadlier than one on an ordinary highway, where there are no walls to smash into. Also, the tunnel is presumably darker, and if you can’t see what’s ahead, it is appropriate to slow down. Mulad is right; why do we want to condition people out of good behavior?

  5. Glinda Says:

    They slow down to adjust to the darker light. A “pre tunnel” consisting of a series of arches that reduce direct sunlight could ameliorate the problem. Example: go to Google Maps and type

  6. Scott Says:

    Yes, drivers should slow down when approaching a tunnel that they cannot see into.

    They should not be braking, however. Drivers should look ahead, notice they are approaching the tunnel, and decelerate gradually rather than hit the brakes.

    I think that better driver education would help. Too many people tailgate as well as jam on the brakes when they should simply decelerate more gradually.

  7. JJM P.E. Says:

    Given that the same thing happens at the Kosciusko Bridge near Albany, NY (a through-arch) I suspect that the sense of confinement has as much to do with it as going under a mountain or river. Drivers feel that they have less room for error, and slow down to compensate.

    It’s even been noted next to concrete barriers and other obstructions.

    I suggest maintaining shoulder width, or even making them wider, as well as tapering the entrance, rather than abruptly narrowing the roadside.

  8. fred_dot_u Says:

    JJM P.E. appears to have the answer for slowing down drivers in residential areas that have had the roadways expanded and “improved” to the point where speeds are excessive for any other uses in a safe manner.

    Let’s put up tunnel walls and tops and slow those cars down!

    yeah, not practical, but even a narrower roadway would probably help in that respect.

  9. Tony P Says:

    fred: On residential streets, the traffic calming tunnel is practical, cheap, pretty, reduces greenhouse gasses…and it works! It’s called a tree canopy.

  10. fred_dot_u Says:

    I agree, Tony P. So many benefits to such a roadway.

  11. Thomas Says:

    This is kind of to be expected. What I don’t understand is people who slow down to go through a green light.

  12. fred_dot_u Says:

    People who slow while entering an intersection might have had the unpleasant experience of encountering someone else who does not stop at red lights. Four decades ago, my driver’s ed instructor taught us to lift off the pedal and hover over the brake pedal when entering an intersection. Motorcycle safety classes suggest to have one’s hands on the brake and clutch levers at intersections.

    If I’m sitting at a red light that turns green, I do not arbitrarily enter the intersection. With a green light, I look left and right before continuing. It’s prevented one crash so far. That’s enough for me to continue the practice.

  13. Smellis Says:

    I agree that Germans are design oriented and efficient, but i don’t think those “pre-tunnel” joists are meant to prepare drivers for entering a tunnel as much as they are there for structural purposes (to hold the wall that separates the 2 directions of travel).

  14. Eduardo Says:

    We face the same in Brazil, especially at the Rodoanel, a road ring around Sao Paulo city. Drivers will slow down or even brake at the entrance of a 2 km long tunnel, causing traffic to be jammed for up to 8 km (about 5 miles). The fear of the darkness and the unknown triggers the instinct of grabbing as much control as you can, so you would even swerve on the brakes if the tunnel was pitch dark, this I can undertand. In the other hand, modern tunnels are full of lights as bright as the sun, even in a tropical country like mine, so there is full vision ahead and yet the instinct prevails… I guess using more the reason and less the instinct could be bennefical for everyone… (as long as this does not reduce safety)

Leave a Reply

Traffic Tom Vanderbilt

How We Drive is the companion blog to Tom Vanderbilt’s New York Times bestselling book, Traffic: Why We Drive the Way We Do (and What It Says About Us), published by Alfred A. Knopf in the U.S. and Canada, Penguin in the U.K, and in languages other than English by a number of other fine publishers worldwide.

Please send tips, news, research papers, links, photos (bad road signs, outrageous bumper stickers, spectacularly awful acts of driving or parking or anything traffic-related), or ideas for my Transport column to me at:

For publicity inquiries, please contact Kate Runde at Vintage:

For editorial inquiries, please contact Zoe Pagnamenta at The Zoe Pagnamenta Agency:

For speaking engagement inquiries, please contact
Kim Thornton at the Random House Speakers Bureau:

Order Traffic from:

Amazon | B&N | Borders
Random House | Powell’s

U.S. Paperback UK Paperback
Traffic UK
Drive-on-the-left types can order the book from

For UK publicity enquiries please contact Rosie Glaisher at Penguin.

Upcoming Talks

April 9, 2008.
California Office of Traffic Safety Summit
San Francisco, CA.

May 19, 2009
University of Minnesota Center for Transportation Studies
Bloomington, MN

June 23, 2009
Driving Assessment 2009
Big Sky, Montana

June 26, 2009
PRI World Congress
Rotterdam, The Netherlands

June 27, 2009
Day of Architecture
Utrecht, The Netherlands

July 13, 2009
Association of Transportation Safety Information Professionals (ATSIP)
Phoenix, AZ.

August 12-14
Texas Department of Transportation “Save a Life Summit”
San Antonio, Texas

September 2, 2009
Governors Highway Safety Association Annual Meeting
Savannah, Georgia

September 11, 2009
Oregon Transportation Summit
Portland, Oregon

October 8
Honda R&D Americas
Raymond, Ohio

October 10-11
INFORMS Roundtable
San Diego, CA

October 21, 2009
California State University-San Bernardino, Leonard Transportation Center
San Bernardino, CA

November 5
Southern New England Planning Association Planning Conference
Uncasville, Connecticut

January 6
Texas Transportation Forum
Austin, TX

January 19
Yale University
(with Donald Shoup; details to come)

Monday, February 22
Yale University School of Architecture
Eero Saarinen Lecture

Friday, March 19
University of Delaware
Delaware Center for Transportation

April 5-7
University of Utah
Salt Lake City
McMurrin Lectureship

April 19
International Bridge, Tunnel and Turnpike Association (Organization Management Workshop)
Austin, Texas

Monday, April 26
Edmonton Traffic Safety Conference
Edmonton, Canada

Monday, June 7
Canadian Association of Road Safety Professionals
Niagara Falls, Ontario

Wednesday, July 6
Fondo de Prevención Vial
Bogotá, Colombia

Tuesday, August 31
Royal Automobile Club
Perth, Australia

Wednesday, September 1
Australasian Road Safety Conference
Canberra, Australia

Wednesday, September 22

Wisconsin Department of Transportation’s
Traffic Incident Management Enhancement Program
Statewide Conference
Wisconsin Dells, WI

Wednesday, October 20
Rutgers University
Center for Advanced Infrastructure and Transportation
Piscataway, NJ

Tuesday, March 8, 2011
Ontario Injury Prevention Resource Centre
Injury Prevention Forum

Monday, May 2
Idaho Public Driver Education Conference
Boise, Idaho

Tuesday, June 2, 2011
California Association of Cities
Costa Mesa, California

Sunday, August 21, 2011
American Association of Motor Vehicle Administrators
Milwaukee, Wisconsin

Wednesday, October 26, 2011
Attitudes: Iniciativa Social de Audi
Madrid, Spain

April 16, 2012
Institute for Sensible Transport Seminar
Gardens Theatre, QUT
Brisbane, Australia

April 17, 2012
Institute for Sensible Transport Seminar
Centennial Plaza, Sydney
Sydney, Australia

April 19, 2012
Institute for Sensible Transport Seminar
Melbourne Town Hall
Melbourne, Australia

January 30, 2013
University of Minnesota City Engineers Association Meeting
Minneapolis, MN

January 31, 2013
Metropolis and Mobile Life
School of Architecture, University of Toronto

February 22, 2013
ISL Engineering
Edmonton, Canada

March 1, 2013
Australian Road Summit
Melbourne, Australia

May 8, 2013
New York State Association of
Transportation Engineers
Rochester, NY

August 18, 2013 “Ingenuity” Conference
San Francisco, CA

September 26, 2013
TransComm 2013
(Meeting of American Association
of State Highway and Transportation
Officials’ Subcommittee on Transportation
Grand Rapids MI



November 2010
« Oct   Dec »

No, you probably won be compensated one million dollars; however, with the right blend of negotiating skills and patience, your efforts will be substantially rewarded!I have seen up to forty thousand dollars added to starting compensation through diligent negotiations. It is a way to significantly raise your standard of living and sense of self, simply by