Minutes - Public Works Committee - 01/20/2004

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JUNE, 2000 ROAD DESIGN ~LANIJAL (ENGLISH) 5-4(3) ' '/'//////?///,/~////)-2'//////.<×~//72.2/72//w/22?//?/?~ COMBID-ED BY-PASS L,4aNE AxND RIGHT-TURN LA.[N'E (To be used only where cross street volume is low) Figure 5-4.01B 5-4.01.06 ~l[edian Acceleration Lane Minnesota highways have a [imited number of median acceleration lanes. Those which have been constructed thus far have favorabie results. At unsignalized intersections with relatively heavy truck volumes, the median acceleration lane provides the [eft turning truck, entering the expressway, the opportunity to accelerate and reduce thc speed differential before enter/ng-the traffic stream. Median accderation lanes should not be constructed indiscriminately. They may be used at locations where there is a high number of trucks turning left onto the mainline, where the e,',dsring median does not provide enough room for a truck to stop in the median when making a two-stage crossing, and where there is a history of high rate of truck accidents.. are: The basic design for a median acceleration lane is shown in Figure 5-4.01 C, the applied design criteria 1. The entenng tl~roat should be wide enough so that a turning truck will be far enough from the th.rough-lane not to have a negative impact on the througt~-[ane traffic. 2. The fane width should be wide enough to provide the accelerating truck added buffer in the zone where the speed differential is the greatest. 3. There should be sufficient length for the truck to accelerate and reduce the speed differential before entering the through-lane. 4. Wlaen near a crossover, the acceleration lane taper shall end before the crossover left-turn lane is developed. [n [997, the 87.5 percentile mass/power ratio for trucks was 192 lb/hp. The rate of acceleration from a stop for these trucks is 0.98 ft/s'" (ITE's 1999 Traffic Engineering Hmadbook), Designers may use the appropriate acceleration rate tbr their design truck. The formula used to calculate speed is: -7-