“First, the use of a single batching plant for the production of two distinct mixes was not viewed as a major obstacle if conducted differently,” they write. “The mix designs, and difficulties with the subcontractor for the concrete, could be traced directly to logistics and planning more than the fundamental need for two distinct batching plants.”
Lighted-Pavement Markers Provide Positive Guidance
Lighted pavement markers appear to reduce lane-keeping violations and illegal movements in three adjacent left-turn lanes, say Roma G. Stevens, P.E., and Jonathan Tydlacka, P.E., assistant research engineers, and Anthony P. Voigt, P.E., research engineer, Texas Transportation Institute; and David C. Worley, P.E., assistant public works director, City of Sugar Land, Tex., in their paper, Evaluation of a Lighted-Pavement Marking System for Lane Delineation.
The lighted pavement markers (LPMs) were used to delineate a triple left-turn movement at a signalized diamond intersection in Sugar Land. The lighted pavement markers are activated at the beginning of the green traffic signal indication for the triple left-turn movement, and the markers stay on until the end of the yellow signal indication.
The intended impact of the pavement markers is to provide positive guidance for lane keeping and reduce illegal movements and crashes on the intersection approach with the triple left-turn assignment. In addition, a dynamic message sign (DMS) is installed 900 feet ahead of the intersection, and its displays allowed travel movements for the three left-turn lanes and an alternate message reminding drivers to stay in their lane.
An evaluation study was conducted with and without the LPMs operating to compare traffic volumes, lane changes, lane-keeping violations and illegal movements between the two study periods (LPM ON and LPM OFF).
“During the LPM ON period, the lighted pavement marker system was in place and active, and during the LPM OFF period, the lighted pavement marker system was in place but was inactive,” say Stevens, Tydlacka, Voigt and Worley. “The DMS stayed active during both study periods. It was determined that the lighted pavement markers appeared to reduce lane-keeping violations and illegal movements. Furthermore, a comparison of six months before and six months after crash data showed some positive results, but due to the small time increment, no statistically significant conclusions could be made.”
The interchange of U.S. 59 at State Highway (SH) 6 in Sugar Land experiences high demand during the peak hours, especially high-directional turning movements from the U.S. 59 southbound (SB) frontage road to SH 6 SB. “The design of the U.S. 59 SB approach was signed and marked to allow two lanes to turn left to the south on SH 6 (one dedicated left-turn only lane and one shared left through lane),” they write. “However, traffic demand for this movement is such that at least two dedicated lanes for left turns are needed during peak hours, with three turn lanes recommended to provide optimal traffic signal operations.”
The City of Sugar Land identified the triple left-turn concept as a potentially beneficial treatment for the left-turn movement from the U.S. 59 SB approach. But triple left-turn operations are not commonly encountered by motorists, so the city planned to provide multiple means of motorist guidance (i.e., signing and marking) to ensure safe operation.
The triple left-turn operation for U.S. 59 SB at SH 6 in Sugar Land began on Nov. 20, 2009, and the LPM system was activated at the same time. The LPMs were installed along the painted dashed lane line tracks along the curve between the left-turn lane on the far left and the middle left-turn lane, as well as between the middle left-turn lane and the far right left-turn lane.
“Each marker emits a white light from multiple light-emitting diodes, and the LPM system is operated 24 hours a day in a steady-burn mode during every traffic signal cycle,” say Stevens, Tydlacka, Voight and Worley. The steady burn pattern mimics the appearance of standard raised pavement markers.
For each cycle, the markers are activated at the beginning of the green traffic signal indication for the U.S. 59 SB movements, and the markers stay on until the end of the yellow signal indication.
Video was recorded with and without the LPMs operating to compare traffic volumes, lane changes, lane-keeping violations and illegal movements between the two periods of recording (LPM ON and LPM OFF). In addition, crash data for a before and an after period were compared to assess the safety effects of LPM system.