Physics Tip Sheet #43 - July 6, 2004

Contact: James Riordon
riordon@aps.org
301-209-3238
American Physical Society

Highlights of this tip sheet include a study predicting a possible end to traffic jams and a new method for moving atoms.

1) Eliminating Traffic Jams with Adaptive Cruise Control
L.C. Davis
Physical Review E, June 2004
http://link.aps.org/abstract/PRE/v69/e066110

Traffic jams could become a thing of the past if as few as one in five cars on the road were piloted with the assistance of adaptive cruise control, according to a new study. Adaptive cruise control is a driver assistance system that automatically adjusts a vehicle's speed to maintain a safe following distance by monitoring the locations of other vehicles via radar or laser ranging devices. Craig Davis of the University of Michigan carried out several simulations, on both single lane roads and multilane roads with onramps, and found that in most cases adaptive cruise control vehicles helped smooth and speed traffic flow. In fact, the simulations showed that on single lane roads with high-speed traffic, equipping just 20% of vehicles with adaptive cruise control prevented jams altogether. The paper points out one potential problem: drivers in manually driven vehicles could have difficulty merging at an onramp because adaptive cruise control vehicles do not attempt to accommodate them, whereas human drivers often would. Adaptive cruise control is standard on many luxury vehicles, and is increasingly available as an option on mid-priced vehicles.

2) Trapping and Guiding Atoms with Solid Optical Fibers
V. I. Balykin et al.
Physical Review A (forthcoming issue)
http://publish.aps.org/DLO/A02Jun04abs_0011.html

In recent years, researchers have succeeded in manipulating individual atoms inside hollow optical fibers. Now, a research group has proposed a method to trap and guide atoms on the outside of solid optical fibers. The technique relies on the short-range evanescent waves that exist near the surface of a fiber that has a diameter smaller that the wavelength of light launched into the fiber. Neutral atoms would be attracted toward the fiber by the evanescent waves, but prevented from colliding with the fiber surface as a result of the atoms' angular momenta. In effect, the atoms take up orbits around the fiber's axis. The researchers suggest that the approach may lead to new ways to store, move, and manipulate atoms.

Journal articles available to journalists on request.

For media assistance with these or other physics stories, contact:

James Riordon
Head of Media Relations
American Physical Society
Ph: +1 301 209 3238
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Email: riordon@aps.org