What goes into setting speed limits on Tallahassee's 4-lane roads? | Street Scene
Well my goodness, in our July 9 Street Scene we gave a heartfelt welcome to our esteemed incoming FHP Director, Colonel Gary Howze ll. And how did we do it? By misspelling the Colonel's last name. My sincere apologies, Colonel Howze. Please consider yourself now officially welcomed. Godspeed.
Complications in setting speed limits
Q. Kris has conducted a little speed limit study provoking thought on what criteria is used for setting speed limits on local streets. There are four very similar 4-lane roads in Tallahassee with different speed limits. Many drivers ignore the apparent inconsistencies and drive the speed they wish.
A. Kris, since you have taken such an interest in the important subject of speed I will do my best to help all of us better understand a few considerations traffic engineers use in determining speed limits. First in play with existing designs is the road and environment: Multiple lanes in each direction or single lane in each direction. Multi-lane divided or non-divided. Urban high density or rural low density. Residential/business or non. At grade intersecting streets or limited access. Multiple access and egress areas or few. And actual traffic studies.
You may have heard of the 85 percentile which is used to establish speed limits on existing roads. This is considered a baseline theory that the majority of drivers are reasonable and prudent; drivers do not want to be involved in a crash; drivers want to reach their destination in the shortest possible time. Therefore it is presumed a speed at or below 85 percent of what speed people drive may be considered as the maximum safe speed for that location.
Looking at your examples: Thomasville Road between Post Road and Live Oak Plantation Road, 45 mph. The 4-lane section of Magnolia Drive, 40 mph. The 4-lane section of Park Avenue, 35 mph. and the 4-lane section of Blair Stone Road, 35 mph.
We can see the 85 percentile was not used to establish speed limits on each of these roads. Oh wait, like Peter Pan once said to Mr. and Mrs. Darling’s children, there’s something I forgot. Politics! Every city or township by nature are political. Capital cities a little more so perhaps and we are no exception. We understand Tallahassee is a political town which, how do I say, does occasionally overflow into the streets.
The things for all of us to remember is exceeding the posted speed is never warranted. Careless driving will cause a traffic crash but it is high speed that kills.
Roundabout coming?
Q. Mary Jane understands a roundabout will be going in next summer at Dempsey Mayo and Miccosukee Roads.
A. My previous statement — "extending Dempsey Mayo Road into Welaunee is many years away" — is based on two known values, Mary Ann.
First, many trees will be sacrificed to accommodate a roundabout here. Secondly, if we are ready for trees to come down, the trees in the way of any type of improvement would have come down a long time ago to improve the safety of this intersection by removing the turning conflicts and driver frustration of this place.
Then there is the Street Scene value. We MUST accommodate a constant stream of walkers, wheelchairs, runners and twice a day school children. The only way to do that safely is to include overhead pedestrian access to and from the Greenway to the north and residents to the south.
There are many workable and safe ‘T’ intersections all over the city, indeed throughout the country, however trees come first on this beautiful canopy road. Let’s just say I am not optimistic about the proposed time line.
Correction: When I wrote "to correct the traffic dilemma at Miccosukee Road and Dempsey Mayo we need to grade and improve the south east shoulder to shift the eastbound lane over 6 to 8 feet to remove the turning traffic conflicts" readers pointed out the shoulder improvement is necessary on the south west side.
Hazards at four-way stop
Q. Evelyn writes: I think four-way stops usually work just fine for city or urban streets. However when driving in a more rural part of the county and two equally trafficked roads — Crump and Miccosukee — come together, with no warning, into a four-way stop intersection, it’s no wonder more crashes have not occurred. It’s especially concerning when darkness descends or when it’s raining. I understand traffic lights are expensive but couldn’t the county at least put a flashing warning sign somewhat ahead of each of the stop signs?
A. I believe you will be happy with recent improvements, Evelyn. Southbound on Crump Road there is now a pictorial, small solid red octagonal sign with black arrowhead (depicting straight ahead) on a yellow background warning of an intersection ahead. This sign is supplemented with the smaller standard black cross on yellow background and rumble strips across the southbound lane.
There is also a pictorial, small solid red octagonal sign with black arrowhead (depicting straight ahead) on a yellow background, warning sign for approaching northbound traffic. Although this advanced warning sign may be hidden behind heavy overgrowth it is also supplemented by the black cross on yellow background intersection warning. It too is supplemented with rumble strips.
Eastbound Miccosukee Road drivers are greeted with the pictorial small solid red octagonal sign with black arrowhead (depicting straight ahead) on a yellow background warning sign and the standard black cross on yellow background as is the westbound traffic. My conclusion is this intersection is now well provided with up-to-date advance warning.
What may be helpful here is the larger stop signs. Accordingly, we request Leon County public works consider retrofitting the large MUTCD R1-1 “oversized” 48” x 48” stop signs at each approach to this intersection.
Dangers at Live Oak Plantation Road
Q. Carolyn had hoped the dangerous intersection of Thomasville Road and Live Oak Plantation Road (LOPR) would gain some attention from the planned multi-use construction. This is a dangerous intersection with drivers from LOPR trying to turn north onto Thomasville Road finding themselves in a lethal game of Pac-Man. We know of one death at this intersection and going by debris, there have been more accidents. Is there any relief in sight?
A. The only solution here and Piedmont Drive is to install full phase fully actuated traffic signals at both locations of which I am on record as supporting. The obvious advantage for a signal at Piedmont Drive is how it will also relieve the congestion and potential for crashes at Piedmont Drive East. I am pleased to say I have witnessed extreme courtesy at this intersection given by northbound drivers allowing LOPR traffic sufficient gaps to merge into Thomasville Road.
Most intersections are not inherently dangerous. By our poor judgment while operating a motor vehicle, we classify the intersection dangerous instead of ourselves.
Philip Stuart is a retired Florida State Trooper, Traffic Operations Projects Engineer and Forensics Expert Witness. Write to crashsites@embarqmail.com.
This article originally appeared on Tallahassee Democrat: Speed limits on Tallahassee's 4-lane roads are inconsistent
