Discussion Topic: Thread for fog-related highway visibility research topics, discussions, data

Thread for fog-related highway visibility research topics, discussions, data

Mark Chandler, FHWA WI Division, mark.chandler@fhwa.dot.gov

05/30/2003

Greetings: I'd like to make this a thread for fog-related highway visibility research topics, discussions, data. I'm promped by Dennis Johnson's 5/28/03 post to this Discussion topic, as well as the following proposal recently sent to the FHWA. Fog proposal (5/27/03) I recently read an article in the Los Angeles Times regarding fog related auto accidents, particularly in the Central Valley of California. The article indicated that in 2001, according to NHTSA figures, 628 people died in crashes associated with foggy conditions. I have occasionally driven highway 99 in foggy conditions and can attest to the hazardous driving conditions. The primary hazard appears that most drivers underestimate the stopping distance required at the speed they are driving and consequently drive faster than their ability to see an obstacle and stop in time. On some sections of highway 99, signs have been placed denoting the distances from a start line. I assume this was done to alert drivers to how far ahead they could see. While this is useful information, in order to be truly useful, the driver must convert this distance into stopping distance and than calculate the appropriate speed to stop within that distance. I suspect this calculation is unlikely to be attempted by most casual drivers. I suggest that these distance signs be replaced by recommended speed signs, which are spaced to correspond to minimum stopping distances at that speed. For instance, a 70 mph sign would be placed at 315 feet from the start line, a 60 mph sign at approximately 240 feet, a 50 mph sign at 175 feet and so on. If upon passing the start line a driver can see the sign that says 70 mph (the furthest sign) than he may assume that he can stop if he sees an obstacle that far away while driving up to 70mph. If the driver, because of foggy conditions, can only see the 30 mph sign when he crosses the start line (the higher mph signs being obscured by fog) than he would know he must travel no more than 30 mph in order to stop if any obstacle comes into view. This is a very low tech and I suspect very inexpensive way of informing motorists what the recommended driving speeds should be under various visibility conditions. While it?s primary purpose would be to inform drivers of save driving speeds during foggy conditions, it would have the added benefit of reminding drivers at night or other inclement weather of their limited ability to see and respond to obstacles ahead. I believe most drivers would intuitively grasp the meaning of these signs without an extensive educational program, certainly all the local drivers would understand their meaning in a relatively short time. Initial installations costs should be small and absent extraordinary changes in car brakes, no adjustments would be required for the life of the signs. Of course not every driver will conform to the recommended driving speeds but every driver will be aware of the risks they are taking if they drive faster than the furthest sign they can see during reduced visibility conditions. Mike Tranbarger Head Deputy District Attorney Los Angeles, CA