Street intersections that are equipped with traffic lights would also be equipped with means for generating audible announcements of approaching emergency vehicles, according to a proposal. The means to generate the announcements would be implemented in the intersection-based subsystems of emergency traffic-light-preemption systems like those described in the two immediately preceding articles and in “Systems Would Preempt Traffic Lights for Emergency Vehicles” (NPO-30573), NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 36.

Preempting traffic lights is not, by itself, sufficient to warn pedestrians at affected intersections that emergency vehicles are approaching. Automated visual displays that warn of approaching emergency vehicles can be helpful as a supplement to preemption of traffic lights, but experience teaches that for a variety of reasons, pedestrians often do not see such displays. Moreover, in noisy and crowded urban settings, the lights and sirens on emergency vehicles are often not noticed until a few seconds before the vehicles arrive.

According to the proposal, the traffic-light preemption subsystem at each intersection would generate an audible announcement — for example, “emergency vehicle approaching, please clear intersection” — whenever a preemption was triggered. The subsystem would estimate the time of arrival of an approaching emergency vehicle by use of vehicle identity, position, and time data from one or more sources that could include units connected to traffic loops and/or transponders connected to diagnostic and navigation systems in participating emergency vehicles. The intersection-based subsystem would then start the announcement far enough in advance to enable pedestrians to leave the roadway before any emergency vehicles arrive.

This work was done by Aaron Bachelder and Conrad Foster of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Electronics/Computers category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management
JPL Mail Stop 202-233
4800 Oak Grove Drive Pasadena
CA 91109-8099
(818) 354-2240
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-30623, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).

Unfortunately the TSP Automated Announcements of Approaching Emergency Vehicles (reference NPO-30623) appears to be missing from our system.

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NASA Tech Briefs Magazine

This article first appeared in the September, 2006 issue of NASA Tech Briefs Magazine.

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