4.1. SR 04-28-1997 - Laserfiche WebLink

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Minnesota Department of Transportation District 3 3725 12th St. N. P.O. Box 370 St. Cloud, MN 56302 April 11, 1997 1997 Mr. Terry Maurer MSA Consulting Engineers - Elk River City Engineer 1326 Energy Park Drive St. Paul, Minnesota 55108 T.H. 169 - CS 7106 City of Elk River Tel: 612/255-4181 Fax: 612/255-3257 Toll Free: 1/800/657-3961 i(320) 6s4-s]os Dear Terry: I received your letter expressing the city council's interest in extending the red/red (all red) timing at signalized intersections along TH 169 in the city of Elk River. I will attempt to answer your questions on how the "all red" is timed and the effects of extending the "all red" interval. The Manual of Uniform Traffic Control Devices says that "the yellow vehicle change interval may be followed by a short all red clearance interval" to clear the intersection.prior next green phase. Past timing practice did not include an all'red interval after the yellow; when the yellow terminated the red and the cross street green appeared simultaneously. At the onset of the green a "startup" time of 1 to 3 seconds (perception/reaction) was expected to provide an intersection clearance similar to the current all red interval. Studies showed that it took 1 to 3 seconds for vehicles to notice the green, decide to go, take foot off the brake, check for traffic, and then accelerate and finally move the vehicle. The practice of using the startup time is diminishing although this clearance time is still available if the green is not "jump started". Our practice is to provide an all red interval in addition to the startup time for additional safety measures. The ail red is figured by adding 20 feet (length of vehicle) to the width of the intersection, ( length from the stop bar to the center of the farthest cross street through lane), then dividing this total by 85% speed (55 mph documented from speed study) in feet per second. The current all red timing is figured with the posted 45 mph speed which yields longer all red times. This statewide methodology provides adequate time for vehicles to clear the intersection without encouraging running of the red light. Would an additional 0.5 to 1.0 seconds have a negative effect on moving traffic? I do not think this small amount of time would adversely'effect travel time on TH 169. We do have serious concerns extending, the all red beyond the statewide guidelines: Regular c0mmu{ets have a tendency to notiCe the interval lengths and use to' their advantage. Adding the additional (0.5 to 1.0) seconds to the eXisting 1.5 interval could encourage red light running. A more critical concern is deviating form the State timing guidelines. For example, ifa driver experiences a 2.0 An equal opportunity employer