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bugs on the highway
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Date: Fri, 25 Aug 95 11:52:56 PDT
From: RISKS Forum
RISKS-LIST: Risks-Forum Digest Friday 25 August 1995 Volume 17 : Issue 29
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Date: Wed, 16 Aug 95 09:21:02 +0200 From: kaiser@acm.org Subject: Like an executioner's axe, on the A8 autoroute
In an August 13 article in "Nice-Matin" -- the daily newspaper of Nice (France) -- Alain Ponzanelli is quoted as saying (my translation):
"I was caught like a fly in a spider's web, trapped by a barrier that came down in front of my car like an executioner's axe. I was badly frightened. And I had to back up on the turnpike, risking an accident, to get out of the trap."
The A8 autoroute (turnpike) has toll plazas at intervals on the highway, and the one in question, like some others, has a high-speed lane for cars equipped for "telepayment" by a badge mounted on the lower left interior of the windshield and validated by a sensor in the telepayment lane marked by lights.
M. Ponzanelli drove into the telepayment lane of the Saint-Isidore toll plaza prepared to slow down for the sensor, but to his surprise the normally-open barrier before the sensor closed ahead of him. He was able to veer off into the emergency turnoff lane to his right, where another normally-open barrier closed ahead of him. At this point he was trapped, not even yet at a place where he could pay by cash and proceed. (The article includes a photograph of the lanes and their barriers.) He shouted and sounded the horn, but no one came to help, and he had to back up on the highway to where he could go forward again to a cash payment lane.
According to unnamed autoroute employees interviewed by Nice-Matin, apparently the computer that controls the telepayment lanes "mixed up" what it was supposed to do with its barriers. One of them said that "electronic chips don't tolerate heat too well". Another said "These incidents happen very seldom. It could be an equipment problem or a problem with badges."
There is no question that M. Ponzanelli holds a valid badge: he is subscribed for at least the whole month. From the photograph it appears that the first barrier that closed ahead of him is well before the sensor, and is intended to close off the lane entirely when the telepayment system isn't operating. Finally, although it's true that electronics may be sensitive to excessive heat, heat is hardly a rare phenomenon in summer on the Cote d'Azur, and it's difficult to believe that the deployment of the electronics doesn't account for that.
Pete kaiser@acm.org
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Date: Wed, 23 Aug 1995 11:09:15 +1000 From: hjm@world.net Subject: Australian "intelligent" road experiment
The Stuttgart experience described in RISKS-17.27 reminds me of another failed experiment with "intelligent" road systems. In the late eighties the Victorian Road Traffic Authority (RTA) managed to get funding for an elaborate trial system for "suggesting" drivers change speed to allow uninterrupted travelling, justified on the basis of potential fuel savings.
About 18 (I am not sure of the exact number) overhead signs were erected on Canterbury Road, that is a main street leading from the eastern suburbs into the city of Melbourne, that has many delays during the peak periods. The signs were all connected via modem to the RTA's traffic management system, and would advise motorists to travel at a suggested speed up to the speed limit or be prepared to stop. The first morning lead inevitably to a number of head to tail accidents, as I believe that the system did not account for traffic conditions, merely the status of the traffic lights ahead so that if you travelled at the recommended speed you could hit a stationary car in front of you.
The system was also very useful for telling drivers when to exceed the speed limit, as the sign would change from the 60 km/h speed limit to "prepare to stop", and with only a little intelligence on the part of the driver, it was soon obvious that if you went faster then 60 km/h you would make the lights. In fact this was the only use for the system, as the delays still occurred and the signs were soon ignored by drivers, except when in a hurry to race the lights.
Needless to say, the trial system was abandoned and all of the signs removed.
Dr. Harley Mackenzie, Principal Operations Research Analyst, Yallourn Energy 114 William Street, Melbourne, Australia +61 3 9207 7719 hjm@world.net
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Date: Mon, 21 Aug 1995 19:47:48 EDT
From: John Carr
``The DM 14.000.000 equipment suggested a speed limit of 120 km/h - during a traffic jam.''
There is a more fundamental problem than software bugs. As was hinted in the original article, posting a speed limit, whether electronic or not, is not necessarily an effective means of controlling traffic. American drivers do not pay much attention to speed limits on major roads (the article was about a German system so the following comments may not apply to it). When I say ``do not pay much attention'', I mean actual speed is only weakly correlated with posted speed. It is not a simple relation like 10 MPH over posted speed limit, although that estimate is close to the average. This behavior was documented in a government study within the past few years.
While I was driving on the New Jersey Turnpike a couple years ago an electronic speed limit/traffic advisory sign told me the speed limit was temporarily reduced to 45 MPH from the normal 55 MPH due to traffic ahead. I and everybody else on the road ignored the sign. We could see well enough to judge for ourselves whether and how much we needed to slow down.
The article about the German system cited a wet road warning. ``Wet road'' is not a useful message. I can see that for myself. If the sign could warn that a sudden storm is coming (or a dust storm, or heavy fog, or invisible icing) that could prevent accidents. Every year or two I read a news story about a massive weather-related accident that might have been averted if drivers had been warned and had slowed down. But the cost to build and run a system which could give adequate warning would probably exceed the savings from reduced accidents (taking a typical estimate that a life is worth on the order of a million dollars).
What do I want from an electronic traffic system? Don't tell me anything unless (1) I won't find out for myself until too late and (2) I can do something in response to the warning. Otherwise the system is just wasting my time and distracting me from driving.
My favorite adaptive road status indication is the hand drawn map I saw getting on the New York State Thruway in Albany. It showed where along the road it was snowing and raining. It was at a tollbooth so it didn't take any of my time or distract me from driving and it told me everything I needed to know (the road was open but conditions were bad) in time for me to react (the worst weather was a hundred miles away).
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End of RISKS-FORUM Digest 17.29
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