GBA’s Innovative Roundabout Boosts Safety in Jasper County

The Challenge

With a busy railroad crossing and a history of accidents, an intersection in southwest Missouri desperately needed improvements.

The intersection in Jasper County at the junction of Missouri Route 171 and Routes YY/96, just northwest of Carl Junction, was particularly dangerous due to the intersection’s proximity to a railroad crossing and history of semi-trucks high centering at the location, resulting in trains crashing into trucks. To make matters worse, there was not enough separation to allow trucks at the stop sign while waiting to turn or cross at the intersection without the rear end of their trailers extending across the track. High speeds along Route 171 were also a concern through the intersection.

The Missouri Department of Transportation (MoDOT) had success with other roundabouts in the area. To address these concerns, they identified the desire to install an innovative roundabout at the intersection. A roundabout would be straightforward, but the railroad crossing presented a unique challenge, one that GBA was ready to tackle.

The Solution

First, GBA studied the traffic volumes at the intersection. Approximately 20 trains crossed the intersection daily, traveling at a maximum speed of 55 mph. This resulted in the west leg of the intersection being blocked for nearly one hour each day.

MoDOT wanted a solution that would serve the community now and into the future. Using the construction year 2021 and design year 2041, traffic volumes on Route 171 were predicted to nearly double. Utilizing an Australian SIDRA software program, a quick stochastic analysis was completed to ensure there would be enough capacity within the proposed roundabout to address the predicted increase in traffic volume. A microsimulation of the intersection operations during a train crossing was performed using VISSIM software.

Subsequently, GBA presented conceptual design recommendations to MoDOT, including:

    • Relocating the center of the innovative roundabout approximately 100 feet east of the existing intersection.
    • Installing a 175-foot inscribed circle diameter and 10-foot raised truck apron to accommodate heavy truck traffic.
    • Reducing speeds as vehicles approach the roundabout from 55 mph to 25 mph.
    • Installing a westbound right-turn bypass lane.

Finally, blank-out signs were installed on two of the roundabout approaches to prevent vehicles from waiting when a train was present. GBA worked closely with the railroad to provide a preemptive connection between the railroad’s infrastructure and the blank-out signs. The blank-out signs were designed to activate when the railroad lights began flashing (approximately 25 seconds before the train entered the intersection) and turn off when the train passed.

Through local public engagement, a detour route was developed for construction, splitting southbound traffic to Route M and northbound traffic to Route H. By splitting the traffic, head-to-head truck traffic was avoided.

Missouri Department of Transportation (MoDOT)

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