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Pulling up to stop bars should allow you to go

Several readers have inquired recently about traffic light signals and their mysterious relationship to those white "stop bars" on the pavement.

Reader Sam Scifres asked if he should stop short of the white bar so that he is able to see it over the hood of his vehicle, which is what someone told him recently. Scifres is sure that this is not the way to go because some streets have traffic light sensors embedded in the stop bars and he wonders if we might fill him in.

Reader Dick Weintraub wrote to say he and his fiancee are in disagreement over a similar issue. Weintraub wrote: "She claims that at most traffic signal intersections there are wires in the ground — mostly hidden by the white paint for crosswalks — that inform a sensor of the traffic at the intersection and therefore controls the traffic signal. I'm of the impression that traffic signals are set on timers in a control box on one corner of the street and are timed and usually based on a traffic study to determine the frequency of change."

Here's the upshot: Many (but not all) intersections have what are called loop detectors embedded in the pavement that do indeed help control signal operation. These are basically wires buried in the asphalt that sense the presence of metal in vehicles. When a car or truck enters an intersection the detector senses that a vehicle is there. Left-turn signals on most main streets throughout the county use these detectors.

The white thermal stop bars at intersections are markers. If someone rolls past the stop bar, the detectors will not register the vehicle, so to address Scifres' question, the recommendation from the traffic signal folks is that motorists stop at intersections with the nose of their vehicle on the stop bar. If a vehicle rolls over the bar, the detector will think the car has passed through the intersection and the traffic signal won't change. You may have noticed that signs reading "Stop here to get green light" have been erected at some intersections.

Pinellas County also operates a traffic management center, which uses technology that combines advanced vehicle detectors, closed-circuit cameras and other electronic communication systems to manage signals by constant monitoring of traffic conditions and making real-time adjustments based on what's happening on the roads. Read more about it at online at

Barricade watch

• In downtown St. Petersburg, Second Street S will be closed today between Fifth and Sixth avenues and Sixth Avenue S will be closed from First to Third streets to allow for removal of event structures from the St. Petersburg Times Festival of Reading at USF. The closures will last until about 4 p.m.

• The closure of Belleview Boulevard from S Druid Road to S Fort Harrison Avenue for drainage and repaving work continues and is expected to wrap up around Thanksgiving. Information on detours and a map can be found at

• Early morning commuters into Hillsborough County should be prepared for the closure of the Interstate 275 entrance and exit ramps at Dr. Martin Luther King Jr. Boulevard (MLK- State Road 574, exit 46B) from 9 tonight to 5 a.m. Monday and again on the same schedule Monday night. Both entrance ramps will be closed to all traffic, which will be detoured north on Nebraska Avenue and then left on Hillsborough Avenue to the ramps to northbound or southbound I-275. If you will be traveling north, continue north and use exit 47A onto eastbound Hillsborough Avenue. Turn right and go south on Nebraska Avenue to MLK.

Until next week, happy and safe motoring!

Please e-mail Dr. Delay at [email protected] to share your traffic concerns, comments and questions. Questions selected for publication may be edited for space and clarity. Follow the Doc on Facebook by searching for Ask Dr. Delay.

Pulling up to stop bars should allow you to go 10/22/11 [Last modified: Saturday, October 22, 2011 4:31am]
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