The Hugh Rowe Thomas Bridge is a six-lane bridge that spans the Black Warrior River, connecting the cities of Tuscaloosa and Northport, Alabama. Wikipedia described it in this way: “The bridge is split in Tuscaloosa to accommodate two major, one-way thoroughfares (Lurleen Wallace Boulevard North and South), before joining together heading towards Northport.”
Drivers who live in the area have grown accustomed to the fact that the speed limit on the bridge is ten miles per hour higher than that of the rest of Lurleen Wallace Boulevard in the vicinity. The speed limit on the bridge is 55 MPH, whereas it is 45 MPH on either side of it.
The cities of Tuscaloosa and Northport passed ordinances establishing the speed limit on their respective sides of the bridge, based on the recommendation of the Alabama Department of Transportation (ALDOT). Each city has jurisdiction over its side of the bridge.
A driver, who is not familiar with the fact that the 55 MPH speed limit on the short length of the bridge area will revert to 45 MPH, might well assume that the increase in the speed limit that begins with the bridge portends an overall higher speed limit.
When asked if it were unusual for the speed limit on a bridge to be higher than that of the road leading to it, an ALDOT engineer, responsible for Transportation Systems Management & Operations, said that the bridge should be considered just as a continuation of the roadway.
When the city of Tuscaloosa in 2021 received an inquiry about the higher speed limit of the bridge, it requested that ALDOT do a speed study.
Such a speed study is based on two factors, involving (1) the 85 percentile method and (2) vertical and horizontal concerns. The 85th percentile speed, as explained by Charles Marohn, “is the speed at or below which 85 percent of the drivers will operate with open roads and favorable conditions. The assumption underlying the 85th percentile speed is that most drivers will operate their vehicle at speeds they perceive to be safe. Speed limits set above or below the 85th percentile speed will create unsafe conditions due to speed differential as some drivers adhere strictly to the law while others drive the naturally-induced speed.”
The ALDOT speed study showed that drivers traveled at varied speeds on the bridge at different times of day. The speed at which they drove was of course to some extent determined by the volume of the traffic on the bridge.
The horizontal and vertical design of a roadway involves such things as how fast a driver can drive on a curve.
Based on the 2021 ALDOT speed study, a recommendation was made to the city to let the bridge speed limit remain at 55 MPH, instead of lowering it to the speed limit of 45 MPH that existed on either side of the bridge.
On the side of the bridge that Tuscaloosa has jurisdiction over, the bridge abruptly ends at University Boulevard. There is a traffic light at the intersection that is not visible to drivers until they go over a rise in the bridge. Signage that is placed before the rise warns of an upcoming change in the speed limit. Drivers who sufficiently slow down will be prepared to stop at a red traffic light. At one time there was a “red light camera” at the intersection that recorded drivers who failed to stop. The 45 MPH signage for Lurleen Wallace Boulevard is also easily seen.
On the side of the bridge that is under Northport jurisdiction, a 55 MPH sign is placed at the very beginning of the bridge. Midway on the bridge similar signs have been located. The signage located off of the bridge, that indicates a reduced speed, is less visible than that of the signs on the bridge. An out of town driver who is crossing the bridge, after driving through downtown Tuscaloosa, might well assume that 55 MPH would still be the speed limit if the signage that is off the road were not seen.
When the concrete bridge becomes icy appropriate warnings are posted, although during the winter there are more accidents on the bridge. Southern drivers don’t see a lot of snow and ice.
There may possibly be other bridges where the speed limit exceeds that of the roads leading to them. But the Hugh Thomas Bridge in T-Town is certainly notable for such an enigmatic circumstance.