1. Introduction

As the plausible deniability of peak oil[1] becomes untenable in the near future,[2] automotive fuel costs are projected to increase sharply,[3] which will drive the increasing popularity of electric and hybrid automotive vehicles. Electric and, to a lesser extent, hybrid vehicles produce very little propulsion system noise, even at full power. All-electric cars will become popular with commuters because commercial grid electric power will continue to be available from coal, natural gas, nuclear, wind, and solar sources. The percentage of these low noise vehicles (LNVs) on the road should increase sharply in the next decade, and pedestrians, used to sensing oncoming traffic from engine noise, will increasingly be involved in accidents by inadvertently stepping into the path of oncoming vehicles.

2. The Problem

As LNVs become more common, pedestrian accidents will increase because of the essentially silent operation of these vehicles. The cost of these unnecessary accidents is hard to project accurately but is likely to be quite significant. It is likely that in later decades, as LNVs dominate vehicular traffic, pedestrians will become accustomed to not relying heavily on audio senses, and the accident rate will decline, but the damage will have been done.

Many vehicles today are required by law to have (sometimes obnoxious) noise-making capability during backing. However, the danger with near-silent moving electric cars and other LNVs is that pedestrians unconsciously rely on their sense of hearing when walking near vehicular traffic.

3. The Solution

I propose to supplement the sound a LNV does make with an audio device. Further, such a device could be constructed such that the sound level it produces is tailored to the environment and operating conditions so that it would not become obnoxious or disturb quiet neighborhoods.

There are many types of sound that can be produced to let pedestrians know a vehicle is approaching. Simulating the sound of a reciprocating engine is an obvious choice. Another method is to sample the low level motor, gear, and tire noise of the LNV and amplify it. Control could be effected by determining the ambient level of sound in the environment, and using that level with knowledge of the vehicle’s speed, compute an appropriate output sound level.

The device would be mounted in an appropriate place within the LNV, with microphones to sample ambient sound as necessary to the sound output computation algorithm employed, and one or more speakers or sound producing devices.

A schematic of the proposed device is shown below in Figure 1:

Figure 1: Schematic diagram of the automotive audio pedestrian safety device.

In quiet neighborhoods, at low speeds, the amount of supplemental sound will be smaller than in, say, a parking lot adjacent to a busy highway. By adapting the sound level to the situation, the control unit will minimize the noise pollution contribution to the environment, while also reducing the probability of an avoidable pedestrian or bicyclist accident.

An item in the Honolulu Star Advertiser newspaper announced a new law requiring similar devices on new elelctric cars on July 14, 2011. Northrop Grumman Corp. declined to file for a patent on the proposed device shortly after it was disclosed by the author in 2007.

[2] http://downdenial.blogspot.com/2007/08/peak-oil-in-mainstream-press.html