Intersection Conflict Warning Systems

Last month we talked about work zone ITS. This month, in the interest of equal time, we will delve into rural ITS. Minnesota DOT and the Enterprise Pooled Fund Study have been leading a nationwide effort to advance and promote intersection warning technologies. I am excited about this for a number of reasons not least of which is that it uses technology in areas where they have not been used before. We are accustomed to seeing ITS deployments on freeways and major arterials in and near cities. But uncontrolled intersections on two lane roads have not benefited – until now.

These systems have been used since 1998 to warn drivers at stop signs that cross traffic is approaching and that it will not stop. System architecture has evolved and  varies still but most include sensors to detect approaching traffic on the main line.  The approach speed is detected and analyzed to see if it is a danger to cross traffic. If so, some form of blank out sign is turned on to warn cross traffic.  These are simple, usually solar powered, and cost as little as $30,000 per intersection.

We have all enjoyed success driving down the number of fatalities and serous injuries on our roads. But there is still much work to be done on rural roads. They account for more than half of all fatalities yet only 30% of the vehicle miles driven. A major portion of those fatalities occur at rural intersections. Drivers stop and then pull right into the path of oncoming vehicles. Usually this is due to line of sight or gap acceptance issues. For whatever reason they fail to truly “see” the oncoming traffic.

Early study results have shown excellent results from intersection warning systems.

There are some ongoing discussions:

  • What should the warning signs look like? Some guidance is available and presentations have been made to the National Committee seeking further direction.
  • What are the legal implications? This is a supplemental device. There is still a stop sign at which drivers must stop and look both ways before proceeding. So the thinking is that even if the warning system failed to warn, the driver is still responsible. Many systems include multiple redundant sensors and a log of traffic detected, speeds, and warning triggers with date and time stamp.
  • These can’t be placed everywhere, so where should they be used? Clearly intersections with high concentrations of crashes should be the first ones. But after that?

Another advantage of these simple systems is their portability. If you have an intersection with frequent crashes and you plan to realign it, or add signals, or some other mitigation when funding becomes available, this is a low cost way of “fixing” the problem until you can afford to do more. Afterwards, you can move the system to another intersection.

What can we, as an industry, do to promote these systems? What questions do you have about system architecture? Are there any issues I haven’t mentioned? Let us know what you think!

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