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TSAB wants to stick with TDOT’s speed limits

The Traffic Safety Advisory Board held a long and thoughtful discussion of the west Turnpike speed limits, deciding to recommend sticking with the TDOT limits, but continue to monitor the situation.

Based on the 85th percentile speeds, city engineer Steve Byrd opined that the 50 mph limit is appropriate for the section that has that limit, as the the 85th percentile driver is going about 3 to 7 miles above the limit.

In the 40-mph section, the 85th percentile speed is about 13 mph above the speed limit, suggesting that a higher limit would be right for the road. However, there are concerns about setting a speed limit that is higher than the road’s official design speed, which is stated to be 40 mph in that section, where there are 5 lanes and no median. Also, board members commented about the presence of Girls Inc. and other youth programs on that section of the Turnpike that produce a lot of turning-vehicle activity at certain times of day. They expressed concern about the possibility of accidents — and liabilities if the speed limit is set higher than the official design speed. However, it seems to be agreed that the redesigned road in that section is safer than it used to be and that the road’s physical alignment is consistent with a 60-mph road (which helps explain why so many people are driving so far over the limit).

There was some sympathy for creating a consistent speed limit, but desire for speed limits that fit the road was stronger, leading to the recommendation to keep the TDOT limits. Regarding consistency of speed limits, Steve Byrd provided the information that after completion of the current construction on Hwy 95 west of this section, the 45 mph speed limit is supposed to remain in place for the 5-lane section of road, which will extend to  a short distance west of Southwood Lane. At that point, the median will begin and the speed limit will be 55 mph until the K-25 site area, where it drops back down to 45 mph.

In response to my comments about determining speed based on the road’s context, the professional traffic engineers in the room told me that this needs to be done before the road is designed, because once a road is built its characteristics will largely determine traffic speed.

One of the context issues is bicycles. TSAB members noted that the 50 mph limit means that many people will choose to drive about 60 mph, and there was concern expressed about the safety of bike lane users on such a fast road. Steve Byrd pointed out that the bike lanes are part of a standard TDOT road design (which suggests that someone judges them to be safe, even though they run alongside fast traffic). He said that he is not aware of guidelines on setting speed limits for roads next to bike lanes.

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